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106-514: Such amyloids have been associated with (but not necessarily as the cause of) more than 50 human diseases, known as amyloidosis , and may play a role in some neurodegenerative diseases . Some of these diseases are mainly sporadic and only a few cases are familial . Others are only familial . Some result from medical treatment . Prions are an infectious form of amyloids that can act as a template to convert other non-infectious forms. Amyloids may also have normal biological functions; for example, in

212-403: A β-sandwich , or a β-solenoid which may be either β-helix or β-roll. Native-like amyloid fibrils in which native β-sheet containing proteins maintain their native-like structure in the fibrils have also been proposed. There are few developed ideas on how the complex backbone topologies of disulfide-constrained proteins, which are prone to form amyloid fibrils (such as insulin and lysozyme), adopt

318-431: A Nuclear Medicine PYP scan, DPD scan or SAP scan are also in use. A sample of tissue can be biopsied or obtained directly from the affected internal organ, but the first-line site of biopsy is subcutaneous abdominal fat , known as a "fat pad biopsy", due to its ease of acquisition. An abdominal fat biopsy is not completely sensitive and may result in false negatives , which means a negative result does not exclude

424-499: A chemical shift anisotropy interaction, each orientation with respect to the magnetic field gives a different resonance frequency. If enough crystallites are present, all the different contributions overlap continuously and lead to a smooth spectrum. Fitting of the pattern in a static ssNMR experiment gives information about the shielding tensor, which are often described by the isotropic chemical shift δ i s o {\displaystyle \delta _{iso}} ,

530-484: A classical liquid-state NMR experiment, molecular tumbling coming from Brownian motion averages anisotropic interactions to zero and they are therefore not reflected in the NMR spectrum. However, in media with no or little mobility (e.g. crystalline powders, glasses, large membrane vesicles, molecular aggregates), anisotropic local fields or interactions have substantial influence on the behaviour of nuclear spins, which results in

636-409: A combination of various steps. Similarly, the exponential phase is not only fibril elongation, but results from a combination of various steps, involving primary nucleation, fibril elongation, but also secondary events. A significant quantity of fibrils resulting from primary nucleation and fibril elongation may be formed during the lag phase and secondary steps, rather than only fibril elongation, can be

742-834: A continuous microwave irradiation from a klystron or a gyrotron , with a frequency close to the corresponding electron paramagnetic resonance (EPR) frequency. The development in the MAS-DNP instrumentation, and the improvement of polarising agents (TOTAPOL, AMUPOL, TEKPOL, etc. ) to achieve a more efficient transfer of polarisation has dramatically reduced experiments times which enabled the observation of surfaces, insensitive isotopes, and multidimensional experiments on low natural abundance nuclei, and diluted species. Solid-state NMR spectroscopy serves as an effective analytical tool in biological, organic, and inorganic chemistry due to its close resemblance to liquid-state spectra while providing additional insights into anisotropic interactions. It

848-517: A dipolar coupling vector at an angle of θ m = 54.7° to a strong external magnetic field have zero dipolar coupling. θ m is called the magic angle . Magic angle spinning is typically used to remove dipolar couplings weaker than the spinning rate. Nuclei with a spin quantum number >1/2 have a non-spherical charge distribution and an associated electric quadrupole moment tensor. The nuclear electric quadrupole moment couples with surrounding electric field gradients. The nuclear quadrupole coupling

954-442: A distal to proximal manner. Autonomic neuropathy can present as orthostatic hypotension but may manifest more gradually with nonspecific gastrointestinal symptoms like constipation, nausea, or early satiety. Amyloidosis of the central nervous system can have more severe and systemic presentations that may include life-threatening arrhythmias, cardiac failure, malnutrition, infection, or death. Neuropathic presentation can depend on

1060-413: A faster fibrillation rate and greater toxicity than synthetic β amyloid peptide. There are multiple classes of amyloid-forming polypeptide sequences. Glutamine-rich polypeptides are important in the amyloidogenesis of Yeast and mammalian prions , as well as trinucleotide repeat disorders including Huntington's disease . When glutamine-rich polypeptides are in a β-sheet conformation, glutamines can brace

1166-600: A human disease. All amyloid fibril proteins start with the letter "A" followed by the protein suffix (and any applicable specification). See below for a list of amyloid fibril proteins which have been found in humans: Transthyretin , variants PNS, ANS, heart, eye, leptomeninges S H β2-microglobulin , variants ANS S H terminal variants), skin (C terminal variants) Aβ protein precursor, variant CNS L H Prion protein variants Prion protein variant CJD, GSS syndrome, fatal insomnia Solid-state NMR Solid-state nuclear magnetic resonance (ssNMR)

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1272-460: A magnetic field that interacts with the dipole moments of other nuclei ( dipolar coupling ). The magnitude of the interaction is dependent on the gyromagnetic ratio of the spin species, the internuclear distance r , and the orientation, with respect to the external magnetic field B , of the vector connecting the two nuclear spins (see figure). The maximum dipolar coupling is given by the dipolar coupling constant d , where γ 1 and γ 2 are

1378-503: A period, the scientific community debated whether or not amyloid deposits are fatty deposits or carbohydrate deposits until it was finally found (in 1859) that they are, in fact, deposits of albumoid proteinaceous material. To date, 37 human proteins have been found to form amyloid in pathology and be associated with well-defined diseases . The International Society of Amyloidosis classifies amyloid fibrils and their associated diseases based upon associated proteins (for example ATTR

1484-418: A role. In fact, the aggregation of a protein generates a variety of aggregates, all of which are likely to be toxic to some degree. A wide variety of biochemical, physiological and cytological perturbations has been identified following the exposure of cells and animals to such species, independently of their identity. The oligomers have also been reported to interact with a variety of molecular targets. Hence, it

1590-403: A series of pulses that extend the performance and the bandwidth of the decoupling (TPPM, SPINAL-64, SWf-TPPM ) Homonuclear decoupling is achieved with multiple-pulse sequences (WAHUHA, MREV-8, BR-24, BLEW-12, FSLG ), or continuous wave modulation (DUMBO, eDUMBO ). Dipolar interactions can also be removed with magic angle spinning . Ultra fast MAS (from 60 kHz up to above 111 kHz)

1696-595: A templating or induced-fit mechanism (this 'nucleated conformational conversion' model), eventually forming fibrils. Normally folded proteins have to unfold partially before aggregation can take place through one of these mechanisms. In some cases, however, folded proteins can aggregate without crossing the major energy barrier for unfolding, by populating native-like conformations as a consequence of thermal fluctuations , ligand release or local unfolding occurring in particular circumstances. In these native-like conformations, segments that are normally buried or structured in

1802-756: A variety of neurological symptoms. Vertebral fractures are also common. A rare development is amyloid purpura , a susceptibility to bleeding with bruising around the eyes, termed "raccoon-eyes". Amyloid purpura is caused by amyloid deposition in the blood vessels and reduced activity of thrombin and factor X , two clotting proteins that lose their function after binding with amyloid. Amyloid deposits in tissue can cause enlargement of structures. Twenty percent of people with AL amyloidosis have an enlarged tongue , that can lead to obstructive sleep apnea , difficulty swallowing , and altered taste. Tongue enlargement does not occur in ATTR or AA amyloidosis. Deposition of amyloid in

1908-410: Is 55 to 60 years old. Without treatment, life expectancy is between six months and four years. In the developed world about one per 1,000 deaths are from systemic amyloidosis. Amyloidosis has been described since at least 1639. The presentation of amyloidosis is broad and depends on the site of amyloid accumulation. The kidney and heart are the most common organs involved. Amyloid deposition in

2014-526: Is a spectroscopy technique used to characterize atomic-level structure and dynamics in solid materials. ssNMR spectra are broader due to nuclear spin interactions which can be categorized as dipolar coupling , chemical shielding, quadrupolar interactions, and j-coupling . These interactions directly affect the lines shapes of experimental ssNMR spectra which can be seen in powder and dipolar patterns. There are many essential solid-state techniques alongside advanced ssNMR techniques that may be applied to elucidate

2120-403: Is a 37-amino acid residue peptide known as islet amyloid polypeptide or 'amylin.' This is stored with insulin in secretory granules in [beta] cells and is co secreted with insulin." (Rang and Dale's Pharmacology, 2015.) Amyloid proteins deposit most commonly inside the knee, followed by hands, wrists, elbow, hip, and ankle, causing joint pain. In males with advanced age (>80 years), there

2226-476: Is an efficient way to average all dipolar interactions, including H– H homonuclear dipolar interactions, which extends the resolution of H spectra and enables the usage of pulse sequences used in solution state NMR. Rotational Echo DOuble Resonance (REDOR) experiments, are a type of heteronuclear dipolar recoupling experiment which enables the re-introduction of heteronuclear dipolar couplings averaged by MAS. The reintroduction of such dipolar coupling reduces

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2332-527: Is associated with mitochondrial dysfunction and a resulting generation of reactive oxygen species (ROS), which can initiate a signalling pathway leading to apoptosis . There are reports that indicate amyloid polymers (such as those of huntingtin, associated with Huntington's disease) can induce the polymerization of essential amyloidogenic proteins, which should be deleterious to cells. Also, interaction partners of these essential proteins can also be sequestered. All these mechanisms of toxicity are likely to play

2438-411: Is attributed to the environmental change, as these dyes intercalate between β-strands to confine their structure. Congo Red positivity remains the gold standard for diagnosis of amyloidosis . In general, binding of Congo Red to amyloid plaques produces a typical apple-green birefringence when viewed under cross-polarized light. Recently, significant enhancement of fluorescence quantum yield of NIAD-4

2544-422: Is crucial because many materials—such as ceramics, glass, polymers, and crystals—exist in a solid phase, where their molecular motion is restricted. Therefore, using other techniques to solve their atomic-level structures and dynamics is hard. ssNMR helps elucidate local structure and dynamics of solids, particularly when other methods, like X-ray diffraction or solution NMR spectroscopy, are insufficient in solving

2650-480: Is currently no evidence of structural or functional similarities among proteins known to form disease-associated amyloids. One third of amyloid disease is hereditary, in which case there is normally an early age of onset. Half of amyloid-related diseases are sporadic and have a late age of onset – in these cases, the protein aggregation may be associated with aging-related decline in protein regulation. Some medical treatments are associated with amyloid disease, but this

2756-464: Is estimated that 10–20% of people with amyloidosis have hypothyroidism . Adrenal infiltration may be harder to appreciate given that its symptoms of orthostatic hypotension and low blood sodium concentration may be attributed to autonomic neuropathy and heart failure. "Amyloid deposits occur in the pancreas of people who also have diabetes mellitus , although it is not known if this is functionally important. The major component of pancreatic amyloid

2862-589: Is found in the urine , organ enlargement is present, or problems are found with multiple peripheral nerves and it is unclear why. Diagnosis is confirmed by tissue biopsy . Due to the variable presentation, a diagnosis can often take some time to reach. Treatment is geared towards decreasing the amount of the involved protein. This may sometimes be achieved by determining and treating the underlying cause. AL amyloidosis occurs in about 3–13 per million people per year and AA amyloidosis in about two per million people per year. The usual age of onset of these two types

2968-564: Is in a β-strand conformation in the fibrils, the remainder forms structured or unstructured loops or tails. For a long time our knowledge of the atomic-level structure of amyloid fibrils was limited by the fact that they are unsuitable for the most traditional methods for studying protein structures. Recent years have seen progress in experimental methods, including solid-state NMR spectroscopy and Cryo-Electron Microscopy . Combined, these methods have provided 3D atomic structures of amyloid fibrils formed by amyloid β peptides, α-synuclein, tau, and

3074-546: Is observed in vitro and possibly in vivo. This phenomenon is important, since it would explain interspecies prion propagation and differential rates of prion propagation, as well as a statistical link between Alzheimer's and type 2 diabetes. In general, the more similar the peptide sequence the more efficient cross-polymerization is, though entirely dissimilar sequences can cross-polymerize and highly similar sequences can even be "blockers" that prevent polymerization. The reasons why amyloid cause diseases are unclear. In some cases,

3180-721: Is one of the largest interactions in NMR spectroscopy, often comparable in size to the Zeeman coupling. When the nuclear quadrupole coupling is not negligible relative to the Zeeman coupling, higher order corrections are needed to describe the NMR spectrum correctly. In such cases, the first-order correction to the NMR transition frequency leads to a strong anisotropic line broadening of the NMR spectrum. However, all symmetric transitions, between m I {\displaystyle m_{I}} and − m I {\displaystyle -m_{I}} levels are unaffected by

3286-406: Is positive in 90% of people with AL amyloidosis. Immunofixation electrophoresis is more sensitive than regular electrophoresis but may not be available in all centers. Alternatively immunohistochemical staining of a bone marrow biopsy looking for dominant plasma cells can be sought in people with a high clinical suspicion for AL amyloidosis but negative electrophoresis. ATTR is now considered to be

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3392-559: Is rare. Amyloid-forming proteins aggregate into distinctive fibrillar forms with a beta-sheet structure. The beta-sheet form of amyloid is proteolysis -resistant, meaning it can not be degraded or broken down. As a result, amyloid deposits into the body's extracellular space. The process of forming amyloid fibrils is thought to have intermediate oligomeric forms. Both the oligomers and amyloid fibrils can be toxic to cells and can interfere with proper organ function. The relative significance of different aggregation species may depend on

3498-419: Is seen in 8.5% of AL amyloidosis and 2.4% of AA amyloidosis. One suggested mechanism for the observed malabsorption is that amyloid deposits in the tips of intestinal villi (fingerlike projections that increase the intestinal area available for absorption of food), begin to erode the functionality of the villi, presenting a sprue -like picture. Both the thyroid and adrenal glands can be infiltrated. It

3604-540: Is significant risk of wild-type transthyretin amyloid deposition in synovial tissue of knee joint, but predominantly in old age deposition of wild type transthyretin is seen in cardiac ventricles. ATTR deposits have been found in ligamentum flavum of patients that underwent surgery for lumbar spinal stenosis . In beta 2-microglobulin amyloidosis, males have high risk of getting carpal tunnel syndrome . Aβ2MG amyloidosis (Hemodialysis associated amyloidosis) tends to deposit in synovial tissue, causing chronic inflammation of

3710-555: Is suspected on clinical grounds in individuals with longstanding infections or inflammatory diseases. AA can be identified by immunohistochemistry staining. Historical classification systems were based on clinical factors. Until the early 1970s, the idea of a single amyloid substance predominated. Various descriptive classification systems were proposed based on the organ distribution of amyloid deposits and clinical findings. Most classification systems included primary (i.e., idiopathic ) amyloidosis, in which no associated clinical condition

3816-499: Is the vacuum permeability . Magic angle spinning (MAS) is a technique routinely used in solid-state NMR to produce narrower NMR and more intense NMR lines. This is achieved by rotating the sample at the magic angle θ m (ca. 54.74°, where cos θ m = 1/3 ) with respect to the direction of the magnetic field , which has the effect to cancel, at least partially, anisotropic nuclear interactions such as dipolar , chemical shift anisotropy , and quadrupolar interactions. To achieve

3922-487: Is the group of diseases and associated fibrils formed by TTR ). A table is included below. Many examples of non-pathological amyloid with a well-defined physiological role have been identified in various organisms, including human . These may be termed as functional or physiological or native amyloid. Amyloids are formed of long unbranched fibers that are characterized by an extended β-sheet secondary structure in which individual β strands (β-strands) (coloured arrows in

4028-410: Is the rate constant of monomer dissociation. The terms on the third line describe the effect of fragmentation, which is assumed to occur homogeneously along fibrils with rate constant k − {\displaystyle k_{-}} . Finally, the terms on the last line describe primary and secondary nucleation respectively. Note that the rate of secondary nucleation is proportional to

4134-410: Is thought to explain the prion strain phenomenon. Amyloid is formed through the polymerization of hundreds to thousands of monomeric peptides or proteins into long fibers. Amyloid formation involves a lag phase (also called nucleation phase ), an exponential phase (also called growth phase ) and a plateau phase (also called saturation phase ), as shown in the figure. Indeed, when

4240-463: Is typically ramped to achieve a more broadband and efficient magnetisation transfer. Spin interactions can be removed ( decoupled ) to increase the resolution of NMR spectra during the detection, or to extend the lifetime of the nuclear magnetization. Heteronuclear decoupling is achieved by radio-frequency irradiation on at the frequency of the nucleus to be decoupled, which is often H. The irradiation can be continuous (continuous wave decoupling ), or

4346-517: Is unlikely that there is a unique mechanism of toxicity or a unique cascade of cellular events. The misfolded nature of protein aggregates causes a multitude of aberrant interactions with a multitude of cellular components, including membranes, protein receptors, soluble proteins, RNAs, small metabolites, etc. In the clinical setting, amyloid diseases are typically identified by a change in the spectroscopic properties of planar aromatic dyes such as thioflavin T , congo red or NIAD-4. In general, this

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4452-710: Is used to characterize chemical composition, structure, local motions, kinetics, and thermodynamics, with the special ability to assign the observed behavior to specific sites in a molecule. It is also crucial in the area of surface and interfacial chemistry. Solid-state NMR is used to study insoluble proteins and proteins such as membrane proteins and amyloid fibrils. The latter topic relates to protein aggregation diseases such as Alzheimer's disease and Parkinson's disease . Solid-state NMR spectroscopy complements solution-state NMR spectroscopy and beam diffraction methods (e.g. X-ray crystallography , electron microscopy ). Despite often requiring isotopic enrichment, ssNMR has

4558-525: The Kronecker delta . The physical interpretation of the various terms in the above master equation is straight forward: the terms on the first line describe the growth of fibrils via monomer addition with rate constant k + {\displaystyle k_{+}} (elongation). The terms on the second line describe monomer dissociation, i.e. the inverse process of elongation. k o f f {\displaystyle k_{\rm {off}}}

4664-736: The gyromagnetic ratios of the nuclei, ℏ {\displaystyle \hbar } is the reduced Planck constant , and μ 0 {\displaystyle \mu _{0}} is the vacuum permeability . In a strong magnetic field, the dipolar coupling depends on the angle θ between the internuclear vector and the external magnetic field B (figure) according to D becomes zero for θ m = arccos ⁡ 1 / 3 = arctan ⁡ 2 ≃ 54.7 ∘ {\displaystyle \theta _{m}=\arccos {\sqrt {1/3}}=\arctan {\sqrt {2}}\simeq 54.7^{\circ }} . Consequently, two nuclei with

4770-578: The kidney often involve the glomerular capillaries and mesangial regions , affecting the organ's ability to filter and excrete waste and retain plasma protein . This can lead to high levels of protein in the urine ( proteinuria ) and nephrotic syndrome . Several types of amyloidosis, including the AL and AA types, are associated with nephrotic syndrome . Approximately 20% and 40–60% of people with AL and AA amyloidosis respectively progress to end-stage kidney disease requiring dialysis . Amyloid deposition in

4876-477: The FUS protein, associated with various neurodegenerative diseases. X-ray diffraction studies of microcrystals revealed atomistic details of core region of amyloid, although only for simplified peptides having a length remarkably shorter than that of peptides or proteins involved in disease. The crystallographic structures show that short stretches from amyloid-prone regions of amyloidogenic proteins run perpendicular to

4982-483: The Hartmann–Hahn condition: where γ {\displaystyle \gamma } are the gyromagnetic ratios , ω R {\displaystyle \omega _{R}} is the spinning rate, and n {\displaystyle n} is an integer. In practice, the pulse power, as well as the length of the contact pulse are experimentally optimised. The power of one contact pulse

5088-442: The NMR line widths, and Q {\displaystyle Q} represent the quality factor of the probe resonances. Magic angle spinning dynamic nuclear polarization (MAS-DNP) is a technique that increases the sensitivity of NMR experiments by several orders of magnitude. It involves transferring the very high electron polarisation from unpaired electrons to nearby nuclei. This is achieved at cryogenic temperatures thorugh

5194-452: The NMR spectra. In ssNMR, specifically designed to analyze solid samples, particularly in the form of powders; molecules are fixed in place, which restricts their motion. This leads to more complex magnetic interactions, such as dipole-dipole coupling, chemical shift anisotropy, and quadrupolar interactions. These complex interactions provide more detailed information about the material's structure. This distinction between solution NMR and ssNMR

5300-488: The abdomen, and spleen enlargement. Accumulation of amyloid proteins in the liver can lead to elevations in serum aminotransferases and alkaline phosphatase , two biomarkers of liver injury, which is seen in about one third of people. Liver enlargement is common. In contrast, spleen enlargement is rare, occurring in 5% of people. Splenic dysfunction, leading to the presence of Howell-Jolly bodies on blood smear, occurs in 24% of people with amyloidosis. Malabsorption

5406-494: The adjacent figure) are arranged in an orientation perpendicular to the long axis of the fiber. Such a structure is known as cross-β structure. Each individual fiber may be 7–13 nanometres in width and a few micrometres in length. The main hallmarks recognised by different disciplines to classify protein aggregates as amyloid is the presence of a fibrillar morphology with the expected diameter, detected using transmission electron microscopy (TEM) or atomic force microscopy (AFM),

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5512-440: The advantage that little sample preparation is required and can be used on not just dry or frozen samples, but also fully hydrated samples or native non-crystalline tissues. Solid-state NMR structure elucidation of proteins has traditionally been based on secondary chemical shifts and spatial contacts mostly between carbon nuclei. Upon fast magic-angle spinning, just like in solution NMR spectroscopy, proton-proton contacts represent

5618-434: The amyloid deposition can affect the heart's ability to pump and fill blood as well as its ability to maintain normal rhythm, which leads to worsening heart function and decline in people's quality of life. People with amyloidosis may have central nervous system involvement, along with peripheral involvement which causes sensory and autonomic neuropathies. Sensory neuropathy develops in a symmetrical pattern and progresses in

5724-561: The amyloid fold; in general, an amyloid protein structure is a different conformation from the one that the antibody recognizes. Amyloidosis Amyloidosis is a group of diseases in which abnormal proteins , known as amyloid fibrils , build up in tissue. There are several non-specific and vague signs and symptoms associated with amyloidosis. These include fatigue, peripheral edema , weight loss , shortness of breath , palpitations , and feeling faint with standing . In AL amyloidosis, specific indicators can include enlargement of

5830-408: The amyloid protein can be determined in various ways: the detection of abnormal proteins in the bloodstream (on protein electrophoresis or light chain determination); binding of particular antibodies to the amyloid found in the tissue (immunohistochemistry); or extraction of the protein and identification of its individual amino acids . Immunohistochemistry can identify AA amyloidosis the majority of

5936-465: The amyloid β-sheet motif. The presence of multiple constraints significantly reduces the accessible conformational space, making computational simulations of amyloid structures more feasible. One complicating factor in studies of amyloidogenic polypeptides is that identical polypeptides can fold into multiple distinct amyloid conformations. This phenomenon is typically described as amyloid polymorphism . It has notable biological consequences given that it

6042-520: The characterization of drug polymorphs and solid dispersions, properties related to bioavailability and stability. Solid-state NMR spectroscopy has been widely used in material science. In solution NMR spectroscopy, a solvent is used to dissolve the sample, enabling it to exist in a highly dynamic state where molecules experience rapid tumbling and translational diffusion. So, the molecules can move around freely and rapidly. This random motion averages out magnetic interactions between nuclei, simplifying

6148-430: The chemical shielding is anisotropic because of the anisotropic distribution of molecular orbitals around the nuclear sites. Under sufficiently fast magic angle spinning, or under the effect of molecular tumbling in solution-state NMR, the anisotropic dependence of the chemical shielding is time-averaged to zero, leaving only the isotropic chemical shift . Nuclear spins exhibit a magnetic dipole moment , which generates

6254-420: The chemical shift anisotropy parameter Δ C S {\displaystyle \Delta _{CS}} , and the asymmetry parameter η {\displaystyle \eta } . The dipolar powder pattern (also Pake pattern) has a very characteristic shape that arises when two nuclear spins are coupled together within a crystallite. The splitting between the maxima (the "horns") of

6360-462: The complete averaging of these interactions, the sample needs to be spun at a rate that is at least higher than the largest anisotropy. Spinning a powder sample at a slower rate than the largest component of the chemical shift anisotropy results in an incomplete averaging of the interaction, and produces a set of spinning sidebands in addition to the isotropic line, centred at the isotropic chemical shift. Spinning sidebands are sharp lines separated from

6466-1684: The concentration f ( t , j ) {\displaystyle f(t,j)} of fibrils of length j {\displaystyle j} (here j {\displaystyle j} represents the number of monomers in an aggregate). ∂ f ( t , j ) ∂ t = 2 k + m ( t ) f ( t , j − 1 ) − 2 k + m ( t ) f ( t , j ) + 2 k o f f f ( t , j + 1 ) − 2 k o f f f ( t , j ) + k − ∑ i = j + 1 ∞ f ( t , i ) − k − ( j − 1 ) f ( t , j ) + k 1 m ( t ) n 1 δ j , n 1 + k 2 m ( t ) n 2 M ( t ) δ j , n 2 {\displaystyle {\begin{aligned}{\frac {\partial f(t,j)}{\partial t}}&=2k_{+}m(t)f(t,j-1)-2k_{+}m(t)f(t,j)\\&+2k_{\rm {off}}f(t,j+1)-2k_{\rm {off}}f(t,j)\\&+k_{-}\sum _{i=j+1}^{\infty }f(t,i)-k_{-}(j-1)f(t,j)\\&+k_{1}m(t)^{n_{1}}\delta _{j,n_{1}}+k_{2}m(t)^{n_{2}}M(t)\delta _{j,n_{2}}\\\\\end{aligned}}} where δ i , j {\displaystyle \delta _{i,j}} denotes

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6572-550: The conformations may have led to different forms of the prion diseases. An unusual secondary structure named α sheet has been proposed as the toxic constituent of amyloid precursor proteins, but this idea is not widely accepted at present. The name amyloid comes from the early mistaken identification by Rudolf Virchow of the substance as starch ( amylum in Latin , from Ancient Greek : ἄμυλον , romanized :  amylon ), based on crude iodine-staining techniques. For

6678-981: The deposits physically disrupt tissue architecture, suggesting disruption of function by some bulk process. An emerging consensus implicates prefibrillar intermediates, rather than mature amyloid fibers, in causing cell death, particularly in neurodegenerative diseases. The fibrils are, however, far from innocuous, as they keep the protein homeostasis network engaged, release oligomers, cause the formation of toxic oligomers via secondary nucleation, grow indefinitely spreading from district to district and, in some cases, may be toxic themselves. Calcium dysregulation has been observed to occur early in cells exposed to protein oligomers. These small aggregates can form ion channels through lipid bilayer membranes and activate NMDA and AMPA receptors. Channel formation has been hypothesized to account for calcium dysregulation and mitochondrial dysfunction by allowing indiscriminate leakage of ions across cell membranes. Studies have shown that amyloid deposition

6784-504: The diagnosis of amyloidosis. However, direct biopsy of the affected organ may still be unnecessary as other less invasive methods of biopsy can also be used, including rectal mucosa, salivary gland, lip, or bone marrow biopsy which can achieve a diagnosis in up to 85% of people. In the amyloid deposition of the joints, there will be a decreased signal in both T1 and T2 weighted MRI images . In amyloidoma, there will be low T1 signal with gadolinium injection and low T2 signal. The type of

6890-412: The dominant processes contributing to fibril growth during the exponential phase. With this new model, any perturbing agents of amyloid fibril formation, such as putative drugs , metabolites , mutations , chaperones , etc., can be assigned to a specific step of fibril formation. In general, amyloid polymerization (aggregation or non-covalent polymerization) is sequence-sensitive, that is mutations in

6996-431: The etiology of amyloidosis. People with amyloidosis may experience dysfunction in various organ systems depending on the location and extent of nervous system involvement. For example, peripheral neuropathy can cause erectile dysfunction, incontinence and constipation, pupillary dysfunction, and sensory loss depending on the distribution of amyloidosis along different peripheral nerves. Accumulation of amyloid proteins in

7102-513: The fact that J is a tensor quantity) describes the interaction of nuclear spins through chemical bonds . J-couplings are not always resolved in solids owing to the typically large linewdiths observed in solid state NMR. Paramagnetic substances are subject to the Knight shift . A powder pattern arises in powdered samples where crystallites are randomly oriented relative to the magnetic field so that all molecular orientations are present. In presence of

7208-416: The filament axis, consistent with the "cross-β" feature of amyloid structure. They also reveal a number of characteristics of amyloid structures – neighboring β-sheets are tightly packed together via an interface devoid of water (therefore referred to as dry interface), with the opposing β-strands slightly offset from each other such that their side-chains interdigitate. This compact dehydrated interface created

7314-409: The first-order frequency contribution. The second-order frequency contribution depends on the P 4 Legendre polynomial , which has zero points at 30.6° and 70.1°. These anisotropic broadenings can be removed using DOR (DOuble angle Rotation) where you spin at two angles at the same time, or DAS (Double Angle Spinning) where you switch quickly between the two angles. Both techniques were developed in

7420-428: The formation of fimbriae in some genera of bacteria , transmission of epigenetic traits in fungi, as well as pigment deposition and hormone release in humans. Amyloids have been known to arise from many different proteins. These polypeptide chains generally form β-sheet structures that aggregate into long fibers; however, identical polypeptides can fold into multiple distinct amyloid conformations. The diversity of

7526-432: The fully folded and possessing a high propensity to aggregate become exposed to the solvent or flexible, allowing the formation of native-like aggregates, which convert subsequently into nuclei and fibrils. This process is called 'native-like aggregation' (green arrows in the figure) and is similar to the 'nucleated conformational conversion' model. A more recent, modern and thorough model of amyloid fibril formation involves

7632-555: The fundamental aspects of solid materials. ssNMR is often combined with magic angle spinning (MAS) to remove anisotropic interactions and improve the sensitivity of the technique. The applications of ssNMR further extend to biology and medicine .    The resonance frequency of a nuclear spin depends on the strength of the magnetic field at the nucleus , which can be modified by isotropic (e.g. chemical shift , isotropic J- coupling ) and anisotropic interactions ( e.g. chemical shift anisotropy , dipolar interactions). In

7738-426: The gastrointestinal system may be caused by a wide range of amyloid disorders and have different presentations depending on the degree of organ involvement. Potential symptoms include weight loss, diarrhea, abdominal pain, heartburn (gastrointestinal reflux), and GI bleeding. Amyloidosis may also affect accessory digestive organs including the liver, and may present with jaundice, fatty stool, anorexia, fluid buildup in

7844-515: The heart can cause both diastolic and systolic heart failure . EKG changes may be present, showing low voltage and conduction abnormalities like atrioventricular block or sinus node dysfunction. On echocardiography , the heart shows a restrictive filling pattern, with normal to mildly reduced systolic function. AA amyloidosis usually spares the heart. Cardiac amyloidosis can present with symptoms of heart failure including shortness of breath, fatigue, and edema. As cardiac amyloidosis progresses,

7950-670: The intensity of the NMR signal compared to a reference spectrum where no dephasing pulse is used. REDOR can be used to measure heteronuclear distances, and are the basis of NMR crystallographic studies. The strong H- H homonuclear dipolar interactions associated with broad NMR lines and short T 2 relaxation time effectively relegate proton for bimolecular NMR. Fast MAS and reduction of dipolar interactions by deuteration have made proton ssNMR as versatile as in solution. This includes spectral dispersion in multi-dimensional experiments and structurally valuable restraints and parameters important for studying material dynamics. Ultra-fast NMR and

8056-429: The intervention of secondary events, such as 'fragmentation', in which a fibril breaks into two or more shorter fibrils, and 'secondary nucleation', in which fibril surfaces (not fibril ends) catalyze the formation of new nuclei. Both secondary events increase the number of fibril ends able to recruit new monomers or oligomers, therefore accelerating fibril formation through a positive feedback mechanism. These events add to

8162-415: The isotropic frequency by a multiple of the spinning rate. Although spinning sidebands can be used to measure anisotropic interactions, they are often undesirable and removed by spinning the sample faster or by recording the data points synchronously with the rotor period. Cross-polarization (CP) if a fundamental RF pulse sequence and a building-block in many solid-state NMR. It is typically used to enhance

8268-562: The lag phase. Fibrils grow subsequently from these nuclei through the addition of monomers in the exponential phase. A different model, called 'nucleated conformational conversion' and marked by blue arrows in the figure below, was introduced later on to fit some experimental observations: monomers have often been found to convert rapidly into misfolded and highly disorganized oligomers distinct from nuclei. Only later on, will these aggregates reorganise structurally into nuclei, on which other disorganised oligomers will add and reorganise through

8374-449: The late 1980s, and require specialized hardware (probe). Multiple quantum magic angle spinning (MQMAS) NMR was developed in 1995 and has become a routine method for obtaining high resolution solid-state NMR spectra of quadrupolar nuclei. A similar method to MQMAS is satellite transition magic angle spinning (STMAS) NMR developed in 2000. The J-coupling or indirect nuclear spin-spin coupling (sometimes also called "scalar" coupling despite

8480-511: The length of the amyloid fibril is built by aligned β-strands. The cross-β pattern is considered a diagnostic hallmark of amyloid structure. Amyloid fibrils are generally composed of 1–8 protofilaments (one protofilament also corresponding to a fibril is shown in the figure), each 2–7 nm in diameter, that interact laterally as flat ribbons that maintain the height of 2–7 nm (that of a single protofilament) and are up to 30 nm wide; more often protofilaments twist around each other to form

8586-511: The line broadening of the NMR spectra. Chemical shielding is a local property of each nuclear site in a molecule or compound, and is proportional to the applied external magnetic field. The external magnetic field induces currents of the electrons in molecular orbitals. These induced currents create local magnetic fields that lead to characteristic changes in resonance frequency. These changes can be predicted from molecular structure using empirical rules or quantum-chemical calculations. In general,

8692-602: The main information on the protein tertiary structure. Solid-state NMR, just like solution NMR, also enables the assessment of protein dynamics, which for membrane proteins in lipid bilayers or even micro-crystalline proteins (anchored by contacts to the surrounding molecules but properly hydrated) are largely retained. Solid-state NMR has also been used to study biomaterials such as bone , teeth , hair , silk , wood , as well as viruses , plants , cells , biopsies , and even live animals. ssNMR spectroscopy finds applications in pharmaceutical research. It allows

8798-401: The mass of aggregates, defined as M ( t ) = ∑ j = n 1 ∞ j f ( t , j ) {\displaystyle M(t)=\sum _{j=n_{1}}^{\infty }jf(t,j)} . Following this analytical approach, it has become apparent that the lag phase does not correspond necessarily to only nucleus formation, but rather results from

8904-515: The most common form of amyloidosis. It may be either age related in wild-type ATTR (ATTRv) or familial transthyretin-associated amyloidosis, is suspected in people with family history of idiopathic neuropathies or heart failure who lack evidence of plasma cell dyscrasias. ATTR can be identified using isoelectric focusing which separates mutated forms of transthyretin. Findings can be corroborated by genetic testing to look for specific known mutations in transthyretin that predispose to amyloidosis. AA

9010-432: The pattern is equal to the dipolar coupling constant d {\displaystyle d} .: where γ 1 and γ 2 are the gyromagnetic ratios of the dipolar-coupled nuclei, r {\displaystyle r} is the internuclear distance, ℏ {\displaystyle \hbar } is the reduced Planck constant , and μ 0 {\displaystyle \mu _{0}}

9116-412: The presence of a cross-β secondary structure, determined with circular dichroism , FTIR , solid-state nuclear magnetic resonance (ssNMR), X-ray crystallography , or X-ray fiber diffraction (often considered the "gold-standard" test to see whether a structure contains cross-β fibres), and an ability to stain with specific dyes, such as Congo red , thioflavin T or thioflavin S . The term "cross-β"

9222-895: The problem. X-ray diffraction is great for studying crystalline materials, but many materials are either amorphous or have significant disorders and are not well represented or identified using X-ray diffraction. ssNMR probes both crystalline and non-crystalline regions, offering insights into the local environments of atoms even in disordered systems. It can also help study electrode and electrolyte materials in solid-state batteries by identifying how ions, like lithium, are transported through solid materials. It also gives information about these materials' structural stability and performance under operating conditions. Solid-state NMR has been successfully used to study metal organic frameworks (MOFS), batteries , surfaces of nanoporous materials, polymers . NMR can also be applied to art conservation. Different salts and moisture levels can be detected through

9328-480: The protein involved and the organ system affected. Diagnosis of amyloidosis generally requires tissue biopsy. The biopsy is assessed for evidence of characteristic amyloid deposits. The tissue is treated with various stains . The most useful stain in the diagnosis of amyloid is Congo red , which, combined with polarized light , makes the amyloid proteins appear apple-green on microscopy . Also, thioflavin T stain may be used. A number of imaging techniques such as

9434-838: The protein that makes the majority of deposits, prefixed with the letter A. For example, amyloidosis caused by transthyretin is termed "ATTR". Deposition patterns vary between people but are almost always composed of just one amyloidogenic protein. Deposition can be systemic (affecting many different organ systems) or organ-specific. Many amyloidoses are inherited , due to mutations in the precursor protein. Other forms are due to different diseases causing overabundant or abnormal protein production – such as with overproduction of immunoglobulin light chains (termed AL amyloidosis ), or with continuous overproduction of acute phase proteins in chronic inflammation (which can lead to AA amyloidosis ). About 60 amyloid proteins have been identified so far. Of those, at least 36 have been associated with

9540-414: The quantity of fibrils is plotted versus time, a sigmoidal time course is observed reflecting the three distinct phases. In the simplest model of 'nucleated polymerization' (marked by red arrows in the figure below), individual unfolded or partially unfolded polypeptide chains (monomers) convert into a nucleus ( monomer or oligomer ) via a thermodynamically unfavourable process that occurs early in

9646-443: The sequence can induce or prevent self-assembly. For example, humans produce amylin , an amyloidogenic peptide associated with type II diabetes, but in rats and mice prolines are substituted in critical locations and amyloidogenesis does not occur. Studies comparing synthetic to recombinant β amyloid peptide in assays measuring rate of fibrillation, fibril homogeneity, and cellular toxicity showed that recombinant β amyloid peptide has

9752-446: The sharpening of the NMR lines enable NMR pulse sequences to capitalize on proton-detection to improve the sensitivity of the experiments compared to the direct detection of a spin-1/2 system (X). Such enhancement factor ξ {\displaystyle \xi } is given by: where γ {\displaystyle \gamma } are the gyromagnetic ratios , W {\displaystyle W} represent

9858-545: The signal of a dilute nuclei with a low gyromagnetic ratio (e.g. C , N ) by magnetization transfer from an abundant nuclei with a high gyromagnetic ratio (e.g. H ), or as a spectral editing method to get through space information (e.g. directed N → C CP in protein spectroscopy). To establish magnetization transfer, RF pulses ("contact pulses") are simultaneously applied on both frequency channels to produce B 1 {\displaystyle B_{1}} fields whose strength fulfil

9964-403: The structure by forming inter-strand hydrogen bonding between its amide carbonyls and nitrogens of both the backbone and side chains. The onset age for Huntington's disease shows an inverse correlation with the length of the polyglutamine sequence , with analogous findings in a C. elegans model system with engineered polyglutamine peptides. Other polypeptides and proteins such as amylin and

10070-545: The synovial tissue in knee, hip, shoulder and interphalangeal joints. Amyloid light chains deposition in shoulder joint causes enlarged shoulders, also known as " shoulder pad sign ". Amyloid light chain depositions can also cause bilateral symmetric polyarthritis. The deposition of amyloid proteins in the bone marrow without causing plasma cell dyscrasias is called amyloidoma. It is commonly found in cervical, lumbar, and sacral vertebrae. Those affected may be presented with bone pain due to bone lysis, lumbar paraparesis , and

10176-474: The throat can cause hoarseness. Amyloidoses can be considered protein misfolding diseases. The vast majority of proteins that have been found to form amyloid deposits are secreted proteins , so the misfolding and formation of amyloid occurs outside cells, in the extracellular space. Of the 37 proteins so far identified as being vulnerable to amyloid formation, only four are cytosolic . Most amyloid-forming proteins are relatively small, but otherwise there

10282-453: The time, but can miss many cases of AL amyloidosis. Laser microdissection with mass spectrometry is the most reliable method of identifying the different forms of amyloidosis. AL was previously considered the most common form of amyloidosis, and a diagnosis often begins with a search for plasma cell dyscrasia , memory B cells producing aberrant immunoglobulins or portions of immunoglobulins. Immunofixation electrophoresis of urine or serum

10388-847: The tongue and periorbital purpura . In wild-type ATTR amyloidosis, non-cardiac symptoms include: bilateral carpal tunnel syndrome , lumbar spinal stenosis , biceps tendon rupture , small fiber neuropathy , and autonomic dysfunction . There are about 36 different types of amyloidosis, each due to a specific protein misfolding . Within these 36 proteins, 19 are grouped into localized forms , 14 are grouped as systemic forms , and three proteins can identify as either. These proteins can become irregular due to genetic effects, as well as through acquired environmental factors . The four most common types of systemic amyloidosis are light chain (AL) , inflammation ( AA ), dialysis-related (Aβ 2 M), and hereditary and old age ( ATTR and wild-type transthyretin amyloid ). Diagnosis may be suspected when protein

10494-412: The typically 7–13 nm wide fibrils. Each protofilament possesses the typical cross-β structure and may be formed by 1–6 β-sheets (six are shown in the figure) stacked on each other. Each individual protein molecule can contribute one to several β-strands in each protofilament and the strands can be arranged in antiparallel β-sheets, but more often in parallel β-sheets. Only a fraction of the polypeptide chain

10600-399: The various steps can be determined from a global fit of a number of time courses of aggregation (for example ThT fluorescence emission versus time) recorded at different protein concentrations. The general master equation approach to amyloid fibril formation with secondary pathways has been developed by Knowles , Vendruscolo , Cohen, Michaels and coworkers and considers the time evolution of

10706-524: The well recognised steps of primary nucleation (formation of the nucleus from the monomers through one of models described above), fibril elongation (addition of monomers or oligomers to growing fibril ends) and dissociation (opposite process). Such a new model is described in the figure on the right and involves the utilization of a master equation that includes all steps of amyloid fibril formation, i.e. primary nucleation, fibril elongation, secondary nucleation and fibril fragmentation. The rate constants of

10812-436: The β amyloid peptide do not have a simple consensus sequence and are thought to aggregate through the sequence segments enriched with hydrophobic residues, or residues with high propensity to form β-sheet structure. Among the hydrophobic residues, aromatic amino-acids are found to have the highest amyloidogenic propensity. Cross-polymerization (fibrils of one polypeptide sequence causing other fibrils of another sequence to form)

10918-413: Was based on the observation of two sets of diffraction lines, one longitudinal and one transverse, that form a characteristic "cross" pattern. There are two characteristic scattering diffraction signals produced at 4.7 and 10 Å (0.47 nm and 1.0 nm), corresponding to the interstrand and stacking distances in β sheets. The "stacks" of β sheet are short and traverse the breadth of the amyloid fibril;

11024-450: Was exploited to super-resolution fluorescence imaging of amyloid fibrils and oligomers. To avoid nonspecific staining, other histology stains, such as the hematoxylin and eosin stain, are used to quench the dyes' activity in other places such as the nucleus, where the dye might bind. Modern antibody technology and immunohistochemistry has made specific staining easier, but often this can cause trouble because epitopes can be concealed in

11130-693: Was identified, and secondary amyloidosis (i.e., secondary to chronic inflammatory conditions). Some classification systems included myeloma-associated, familial, and localized amyloidosis. The modern era of amyloidosis classification began in the late 1960s with the development of methods to make amyloid fibrils soluble. These methods permitted scientists to study the chemical properties of amyloids. Descriptive terms such as primary amyloidosis, secondary amyloidosis, and others (e.g., senile amyloidosis), which are not based on cause, provide little useful information and are no longer recommended. The modern classification of amyloid disease tends to use an abbreviation of

11236-609: Was termed a steric-zipper interface. There are eight theoretical classes of steric-zipper interfaces, dictated by the directionality of the β-sheets (parallel and anti-parallel) and symmetry between adjacent β-sheets. A limitation of X-ray crystallography for solving amyloid structure is represented by the need to form microcrystals, which can be achieved only with peptides shorter than those associated with disease. Although bona fide amyloid structures always are based on intermolecular β-sheets, different types of "higher order" tertiary folds have been observed or proposed. The β-sheets may form

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