99-852: Steroid 21-hydroxylase is a protein that in humans is encoded by the CYP21A2 gene . The protein is an enzyme that hydroxylates steroids at the C21 position on the molecule. Naming conventions for enzymes are based on the substrate acted upon and the chemical process performed. Biochemically, this enzyme is involved in the biosynthesis of the adrenal gland hormones aldosterone and cortisol , which are important in blood pressure regulation , sodium homeostasis and blood sugar control . The enzyme converts progesterone and 17α-hydroxyprogesterone into 11-deoxycorticosterone and 11-deoxycortisol , respectively, within metabolic pathways which in humans ultimately lead to aldosterone and cortisol creation—deficiency in
198-516: A carboxyl group, and a variable side chain are bonded . Only proline differs from this basic structure as it contains an unusual ring to the N-end amine group, which forces the CO–NH amide moiety into a fixed conformation. The side chains of the standard amino acids, detailed in the list of standard amino acids , have a great variety of chemical structures and properties; it is the combined effect of all of
297-470: A gene may be duplicated before it can mutate freely. However, this can also lead to complete loss of gene function and thus pseudo-genes . More commonly, single amino acid changes have limited consequences although some can change protein function substantially, especially in enzymes . For instance, many enzymes can change their substrate specificity by one or a few mutations. Changes in substrate specificity are facilitated by substrate promiscuity , i.e.
396-605: A heme cofactor binding loop. Each subunit in the human enzyme consists of a total of 13 α-helices and 9 β-strands that folds into a triangular prism-like tertiary structure . The iron(III) heme group that defines the active site resides in the center of each subunit. The human enzyme binds one substrate at a time. In contrast, the well-characterized bovine enzyme can bind two substrates. The human and bovine enzyme share 80% amino acid sequence identity, but are structurally different, particularly in loop regions, and also evident in secondary structure elements. Variations of
495-654: A certain disease or condition. If the primers are not designed carefully, they may bind to both the CYP21A2 and the CYP21A1P pseudogene, or to different segments of the RCCX cluster, resulting in false-positive or false-negative results. Therefore, PCR for the CYP21A2 requires the use of locus-specific primers that can distinguish between the gene and the pseudogene, and between different RCCX modules. Moreover, PCR may not be able to detect complex variants such as large gene conversions , deletions , or duplications , which are frequent in
594-552: A combination of sequence, structure and function, and they can be combined in many different ways. In an early study of 170,000 proteins, about two-thirds were assigned at least one domain, with larger proteins containing more domains (e.g. proteins larger than 600 amino acids having an average of more than 5 domains). Most proteins consist of linear polymers built from series of up to 20 different L -α- amino acids. All proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group,
693-403: A defined conformation . Proteins can interact with many types of molecules, including with other proteins , with lipids , with carbohydrates , and with DNA . It has been estimated that average-sized bacteria contain about 2 million proteins per cell (e.g. E. coli and Staphylococcus aureus ). Smaller bacteria, such as Mycoplasma or spirochetes contain fewer molecules, on
792-834: A detailed review of the vegetable proteins at the Connecticut Agricultural Experiment Station . Then, working with Lafayette Mendel and applying Liebig's law of the minimum , which states that growth is limited by the scarcest resource, to the feeding of laboratory rats, the nutritionally essential amino acids were established. The work was continued and communicated by William Cumming Rose . The difficulty in purifying proteins in large quantities made them very difficult for early protein biochemists to study. Hence, early studies focused on proteins that could be purified in large quantities, including those of blood, egg whites, and various toxins, as well as digestive and metabolic enzymes obtained from slaughterhouses. In
891-478: A little ambiguous and can overlap in meaning. Protein is generally used to refer to the complete biological molecule in a stable conformation , whereas peptide is generally reserved for a short amino acid oligomers often lacking a stable 3D structure. But the boundary between the two is not well defined and usually lies near 20–30 residues. Polypeptide can refer to any single linear chain of amino acids, usually regardless of length, but often implies an absence of
990-531: A module count is two or more, there is only one copy of each functional gene rest being non-coding pseudogenes with the exception of the C4 gene which always has active copies. Due to the high degree of homology between the CYP21A2 gene and the CYP21A1P pseudogene and the complexity of the RCCX locus, it is difficult to perform molecular diagnostics for CYP21A2 . The pseudogene can have single-nucleotide polymorphisms (SNP) that are identical or similar to those in
1089-410: A particular cell or cell type is known as its proteome . The chief characteristic of proteins that also allows their diverse set of functions is their ability to bind other molecules specifically and tightly. The region of the protein responsible for binding another molecule is known as the binding site and is often a depression or "pocket" on the molecular surface. This binding ability is mediated by
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#17328730795381188-469: A product of a reaction catalyzed by CYP21, as their primary glucocorticoid hormone with mineralocorticoid properties. This suggests the presence of a complex and highly specific corticosteroid signaling pathway that emerged at least half a billion years ago during early vertebrate evolution. In vertebrates, such as fish, amphibians, reptiles, birds, and mammals, Cyp21 participates in the biosynthesis of glucocorticoids and mineralocorticoids, therefore, Cyp21
1287-500: A protein carries out its function: for example, enzyme kinetics studies explore the chemical mechanism of an enzyme's catalytic activity and its relative affinity for various possible substrate molecules. By contrast, in vivo experiments can provide information about the physiological role of a protein in the context of a cell or even a whole organism . In silico studies use computational methods to study proteins. Proteins may be purified from other cellular components using
1386-411: A protein is defined by the sequence of a gene, which is encoded in the genetic code . In general, the genetic code specifies 20 standard amino acids; but in certain organisms the genetic code can include selenocysteine and—in certain archaea — pyrrolysine . Shortly after or even during synthesis, the residues in a protein are often chemically modified by post-translational modification , which alters
1485-539: A protein that fold into distinct structural units. Domains usually also have specific functions, such as enzymatic activities (e.g. kinase ) or they serve as binding modules (e.g. the SH3 domain binds to proline-rich sequences in other proteins). Short amino acid sequences within proteins often act as recognition sites for other proteins. For instance, SH3 domains typically bind to short PxxP motifs (i.e. 2 prolines [P], separated by two unspecified amino acids [x], although
1584-486: A role in biological recognition phenomena involving cells and proteins. Receptors and hormones are highly specific binding proteins. Transmembrane proteins can also serve as ligand transport proteins that alter the permeability of the cell membrane to small molecules and ions. The membrane alone has a hydrophobic core through which polar or charged molecules cannot diffuse . Membrane proteins contain internal channels that allow such molecules to enter and exit
1683-406: A series of purification steps may be necessary to obtain protein sufficiently pure for laboratory applications. To simplify this process, genetic engineering is often used to add chemical features to proteins that make them easier to purify without affecting their structure or activity. Here, a "tag" consisting of a specific amino acid sequence, often a series of histidine residues (a " His-tag "),
1782-432: A solution known as a crude lysate . The resulting mixture can be purified using ultracentrifugation , which fractionates the various cellular components into fractions containing soluble proteins; membrane lipids and proteins; cellular organelles , and nucleic acids . Precipitation by a method known as salting out can concentrate the proteins from this lysate. Various types of chromatography are then used to isolate
1881-451: A specific 3D structure that determines its activity. A linear chain of amino acid residues is called a polypeptide . A protein contains at least one long polypeptide. Short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides . The individual amino acid residues are bonded together by peptide bonds and adjacent amino acid residues. The sequence of amino acid residues in
1980-441: A variety of techniques such as ultracentrifugation , precipitation , electrophoresis , and chromatography ; the advent of genetic engineering has made possible a number of methods to facilitate purification. To perform in vitro analysis, a protein must be purified away from other cellular components. This process usually begins with cell lysis , in which a cell's membrane is disrupted and its internal contents released into
2079-432: A vast array of functions within organisms, including catalysing metabolic reactions , DNA replication , responding to stimuli , providing structure to cells and organisms , and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes , and which usually results in protein folding into
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#17328730795382178-603: Is a group of proteins belonging the class of major histocompatibility complex (MHC). Unlike other MHC types such as MHC class I and MHC class II , of which their structure and functions in immune response are well defined, MHC class III are poorly defined structurally and functionally. They are not involved in antigen binding (the process called antigen presentation , a classic function of MHC proteins). Only few of them are actually involved in immunity while many are signalling molecules in other cell communications. They are mainly known from their genes because their gene cluster
2277-541: Is a member of the cytochrome P450 family of monooxygenase enzymes, the protein has 494 amino acid residues with a molecular weight of 55,000. This enzyme is at most 28% homologous to other P-450 enzymes that have been studied. Structurally, the protein contains an evolutionarily conserved core of four α-helix bundles (the importance of such genetic conservation is in demonstrating the functional importance of this aspect of this protein's structure). In addition, it has two additional alpha helices, two sets of β-sheets , and
2376-532: Is about 28% of the total MHC genes (224). The region previously considered within MHC class III gene cluster that contains genes for TNFs is now known as MHC class IV or inflammatory region. In contrast to other MHC proteins, MHC class III proteins are produced by liver cells ( hepatocytes ) and special white blood cells ( macrophages ), among others. MHC class III genes are located on chromosome 6 (6p21.3) in humans. It covers 700 kb and contains 61 genes. The gene cluster
2475-427: Is almost exclusively expressed in the adrenal gland. As of 2023, the main subcellular location for the encoded protein in human cells is not known, and is pending cell analysis. The enzyme, steroid 21-hydroxylase hydroxylates steroids at the C21 position. Steroids are a group of naturally occurring and synthetically produced organic compounds, steroids all share a four ring primary structure. The enzyme catalyzes
2574-412: Is approximately 1.3 x 10 Ms at 37 °C. This makes it the most catalytically efficient P450 enzyme of those reported to date, and catalytically more efficient than the closely related bovine steroid 21-hydroxylase enzyme. C-H bond breaking to create a primary carbon radical is thought to be the rate-limiting step in the hydroxylation. Genetic variants in the CYP21A2 gene cause a disturbance in
2673-554: Is associated with mild and clinically silent cortisol impairment, but an excess of androgens post-puberty. Non-classical congenital adrenal hyperplasia caused by 21-hydroxylase deficiency (NCCAH) is a milder and late-onset congenital adrenal hyperplasia. Its prevalence rate in different ethnic groups varies from 1 in 1000 to 1 in 50 . Some people affected by the condition have no relevant signs and symptoms, while others experience symptoms of hyperandrogenism . Women with NCCAH usually have normal female genitalia at birth. In later life,
2772-414: Is attached to one terminus of the protein. As a result, when the lysate is passed over a chromatography column containing nickel , the histidine residues ligate the nickel and attach to the column while the untagged components of the lysate pass unimpeded. A number of different tags have been developed to help researchers purify specific proteins from complex mixtures. MHC class III MHC class III
2871-419: Is essential for the biosynthesis of cortisol and aldosterone . Steroid 21-hydroxylase is a cytochrome P450 enzyme that is notable for its substrate specificity and relatively high catalytic efficiency . Like other cytochrome P450 enzymes, steroid 21-hydroxylase participates in the cytochrome P450 catalytic cycle and engages in one-electron transfer with NADPH - P450 reductase . Steroid 21-hydroxylase
2970-450: Is essential for the regulation of stress response, electrolyte balance and blood pressure, immune system, and metabolism in vertebrates. Cyp21 is relatively conserved among mammals, and shows some variations in its structure, expression, and regulation. Rhesus macaques and orangutans possess two copies of Cyp21 , while chimpanzees have three, still, a pseudogene ( CYP21A1P ) is only present in humans among primates. Steroid 21-hydroxylase
3069-628: Is found in hard or filamentous structures such as hair , nails , feathers , hooves , and some animal shells . Some globular proteins can also play structural functions, for example, actin and tubulin are globular and soluble as monomers, but polymerize to form long, stiff fibers that make up the cytoskeleton , which allows the cell to maintain its shape and size. Other proteins that serve structural functions are motor proteins such as myosin , kinesin , and dynein , which are capable of generating mechanical forces. These proteins are crucial for cellular motility of single celled organisms and
21-Hydroxylase - Misplaced Pages Continue
3168-469: Is higher in prokaryotes than eukaryotes and can reach up to 20 amino acids per second. The process of synthesizing a protein from an mRNA template is known as translation . The mRNA is loaded onto the ribosome and is read three nucleotides at a time by matching each codon to its base pairing anticodon located on a transfer RNA molecule, which carries the amino acid corresponding to the codon it recognizes. The enzyme aminoacyl tRNA synthetase "charges"
3267-409: Is highly specific for hydroxylation of progesterone and 17-hydroxyprogesterone. This is in marked contrast to the evolutionarily and functionally related P450 enzyme 17-hydroxylase , which has a broad range of substrates. The chemical reaction in which steroid 21-hydroxylase catalyzes the addition of hydroxyl (-OH) to the C21 position of progesterone , 17α-hydroxyprogesterone and 21-desoxycortisone
3366-461: Is inefficient for polypeptides longer than about 300 amino acids, and the synthesized proteins may not readily assume their native tertiary structure . Most chemical synthesis methods proceed from C-terminus to N-terminus, opposite the biological reaction. Most proteins fold into unique 3D structures. The shape into which a protein naturally folds is known as its native conformation . Although many proteins can fold unassisted, simply through
3465-476: Is localized in microsomes of endoplasmic reticulum membranes within adrenal cortex . It is one of three microsomal steroidogenic cytochrome P450 enzymes, the others being steroid 17-hydroxylase and aromatase . Unlike other enzymes of the cytochrome P450 superfamily of enzymes that are expressed in multiple tissues, with most abundant expression in the liver, in adult humans steroid 21-hydroxylase, along with steroid 11β-hydroxylase and aldosterone synthase ,
3564-404: Is often enormous—as much as 10 -fold increase in rate over the uncatalysed reaction in the case of orotate decarboxylase (78 million years without the enzyme, 18 milliseconds with the enzyme). The molecules bound and acted upon by enzymes are called substrates . Although enzymes can consist of hundreds of amino acids, it is usually only a small fraction of the residues that come in contact with
3663-469: Is present between those of class I and class II . The gene cluster was discovered when genes (specifically those of complement components C2 , C4 , and factor B ) were found in between class I and class II genes on the short (p) arm of human chromosome 6 . It was later found that it contains many genes for different signaling molecules such as tumour necrosis factors (TNFs) and heat shock proteins . More than 60 MHC class III genes are described, which
3762-532: Is the code for methionine . Because DNA contains four nucleotides, the total number of possible codons is 64; hence, there is some redundancy in the genetic code, with some amino acids specified by more than one codon. Genes encoded in DNA are first transcribed into pre- messenger RNA (mRNA) by proteins such as RNA polymerase . Most organisms then process the pre-mRNA (also known as a primary transcript ) using various forms of post-transcriptional modification to form
3861-496: Is the most complex gene cluster in the human genome. The number of RCCX segments varies between one and four in a chromosome , with the prevalence of approximately 15% for monomodular, 75% for bimodular ( STK19-C4A-CYP21A1P-TNXA-STK19B-C4B-CYP21A2-TNXB ), and 10% for trimodular in Europeans. The quadrimodular structure of the RCCX unit is very rare. In a monomodular structure, all of the genes are functional i.e. protein-coding , but if
3960-408: Is the most gene-dense region of the human genome. They are basically similar with those of other animals. The functions of many genes are yet unknown. Many retroelements such as human endogenous retrovirus (HERV) and Alu elements are located in the cluster. The region containing genes STK19 (G11)/C4/Z/ CYP21 /X/Y , varying in size from 142 to 214 kb, is known as the most complex gene cluster in
4059-442: Is unable to detect the junction sites of chimeras. The CYP21A2 gene is prone to mismatch and rearrangement, producing different types of complex variations that include copy number variants , large gene conversions , small insertions / deletions , and single-nucleotide (SNP) variants. Southern blotting is not capable of detecting all these types of variants simultaneously. Besides that, southern blotting requires genetic analysis of
21-Hydroxylase - Misplaced Pages Continue
4158-556: The Tenascin X gene TNXB and STK19 . MHC class III is the most gene-dense region of the human genome, containing many genes that have, as of 2023 - unknown functions or structures. Inside the MHC class III , CYP21A2 is located within the RCCX cluster (an abbreviation composed of the names of the genes RP (a former name for STK19 serine/threonine kinase 19), C4 , CYP21 and TNX ), which
4257-486: The amino acid leucine for which he found a (nearly correct) molecular weight of 131 Da . Early nutritional scientists such as the German Carl von Voit believed that protein was the most important nutrient for maintaining the structure of the body, because it was generally believed that "flesh makes flesh." Around 1862, Karl Heinrich Ritthausen isolated the amino acid glutamic acid . Thomas Burr Osborne compiled
4356-424: The chemical reaction in which the hydroxyl group (-OH) is added at the C21 position of the steroid biomolecule . This location is on a side chain of the D ring. The enzyme is a member of the cytochrome P450 superfamily of monooxygenase enzymes. The cytochrome P450 enzymes catalyze many reactions involved in drug metabolism and synthesis of cholesterol , steroids and other lipids . Steroid 21-hydroxylase
4455-578: The mouse genome , the Cyp21a2 is a pseudogene and the Cyp21a1 is a functional gene. In the chicken and quail , there is only a single Cyp21 gene, which locus is located between complement component C4 and TNX gene, along with Cenpa . CYP21A2 in humans is located in chromosome 6 , in the major histocompatibility complex III (MHC class III) close to the Complement component 4 genes C4A and C4B ,
4554-644: The muscle sarcomere , with a molecular mass of almost 3,000 kDa and a total length of almost 27,000 amino acids. Short proteins can also be synthesized chemically by a family of methods known as peptide synthesis , which rely on organic synthesis techniques such as chemical ligation to produce peptides in high yield. Chemical synthesis allows for the introduction of non-natural amino acids into polypeptide chains, such as attachment of fluorescent probes to amino acid side chains. These methods are useful in laboratory biochemistry and cell biology , though generally not for commercial applications. Chemical synthesis
4653-645: The sperm of many multicellular organisms which reproduce sexually . They also generate the forces exerted by contracting muscles and play essential roles in intracellular transport. A key question in molecular biology is how proteins evolve, i.e. how can mutations (or rather changes in amino acid sequence) lead to new structures and functions? Most amino acids in a protein can be changed without disrupting activity or function, as can be seen from numerous homologous proteins across species (as collected in specialized databases for protein families , e.g. PFAM ). In order to prevent dramatic consequences of mutations,
4752-493: The 1700s by Antoine Fourcroy and others, who often collectively called them " albumins ", or "albuminous materials" ( Eiweisskörper , in German). Gluten , for example, was first separated from wheat in published research around 1747, and later determined to exist in many plants. In 1789, Antoine Fourcroy recognized three distinct varieties of animal proteins: albumin , fibrin , and gelatin . Vegetable (plant) proteins studied in
4851-562: The 1950s, the Armour Hot Dog Company purified 1 kg of pure bovine pancreatic ribonuclease A and made it freely available to scientists; this gesture helped ribonuclease A become a major target for biochemical study for the following decades. The understanding of proteins as polypeptides , or chains of amino acids, came through the work of Franz Hofmeister and Hermann Emil Fischer in 1902. The central role of proteins as enzymes in living organisms that catalyzed reactions
4950-498: The 20,000 or so proteins encoded by the human genome, only 6,000 are detected in lymphoblastoid cells. Proteins are assembled from amino acids using information encoded in genes. Each protein has its own unique amino acid sequence that is specified by the nucleotide sequence of the gene encoding this protein. The genetic code is a set of three-nucleotide sets called codons and each three-nucleotide combination designates an amino acid, for example AUG ( adenine – uracil – guanine )
5049-516: The EC number system provides a functional classification scheme. Similarly, the gene ontology classifies both genes and proteins by their biological and biochemical function, but also by their intracellular location. Sequence similarity is used to classify proteins both in terms of evolutionary and functional similarity. This may use either whole proteins or protein domains , especially in multi-domain proteins . Protein domains allow protein classification by
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#17328730795385148-709: The ability of many enzymes to bind and process multiple substrates . When mutations occur, the specificity of an enzyme can increase (or decrease) and thus its enzymatic activity. Thus, bacteria (or other organisms) can adapt to different food sources, including unnatural substrates such as plastic. Methods commonly used to study protein structure and function include immunohistochemistry , site-directed mutagenesis , X-ray crystallography , nuclear magnetic resonance and mass spectrometry . The activities and structures of proteins may be examined in vitro , in vivo , and in silico . In vitro studies of purified proteins in controlled environments are useful for learning how
5247-405: The addition of a single methyl group to a binding partner can sometimes suffice to nearly eliminate binding; for example, the aminoacyl tRNA synthetase specific to the amino acid valine discriminates against the very similar side chain of the amino acid isoleucine . Proteins can bind to other proteins as well as to small-molecule substrates. When proteins bind specifically to other copies of
5346-595: The alpha carbons are roughly coplanar . The other two dihedral angles in the peptide bond determine the local shape assumed by the protein backbone. The end with a free amino group is known as the N-terminus or amino terminus, whereas the end of the protein with a free carboxyl group is known as the C-terminus or carboxy terminus (the sequence of the protein is written from N-terminus to C-terminus, from left to right). The words protein , polypeptide, and peptide are
5445-531: The amino acid side chains in a protein that ultimately determines its three-dimensional structure and its chemical reactivity. The amino acids in a polypeptide chain are linked by peptide bonds . Once linked in the protein chain, an individual amino acid is called a residue, and the linked series of carbon, nitrogen, and oxygen atoms are known as the main chain or protein backbone. The peptide bond has two resonance forms that contribute some double-bond character and inhibit rotation around its axis, so that
5544-574: The binding of a substrate molecule to an enzyme's active site , or the physical region of the protein that participates in chemical catalysis. In solution, proteins also undergo variation in structure through thermal vibration and the collision with other molecules. Proteins can be informally divided into three main classes, which correlate with typical tertiary structures: globular proteins , fibrous proteins , and membrane proteins . Almost all globular proteins are soluble and many are enzymes. Fibrous proteins are often structural, such as collagen ,
5643-570: The body of a multicellular organism. These proteins must have a high binding affinity when their ligand is present in high concentrations, but must also release the ligand when it is present at low concentrations in the target tissues. The canonical example of a ligand-binding protein is haemoglobin , which transports oxygen from the lungs to other organs and tissues in all vertebrates and has close homologs in every biological kingdom . Lectins are sugar-binding proteins which are highly specific for their sugar moieties. Lectins typically play
5742-444: The case of the CYP21A2 . Southern blotting , a method used for detecting and quantifying a specific DNA sequence in DNA samples, also has limitations in analyzing CYP21A2 . This method is time-consuming and requires a large amount of good-quality DNA, which makes it less applicable in routine diagnostic settings. This method comes with a radioactive biohazard, which poses safety concerns and makes it labor-intensive. Southern blotting
5841-558: The cell is as enzymes , which catalyse chemical reactions. Enzymes are usually highly specific and accelerate only one or a few chemical reactions. Enzymes carry out most of the reactions involved in metabolism , as well as manipulating DNA in processes such as DNA replication , DNA repair , and transcription . Some enzymes act on other proteins to add or remove chemical groups in a process known as posttranslational modification. About 4,000 reactions are known to be catalysed by enzymes. The rate acceleration conferred by enzymatic catalysis
5940-436: The cell surface and an effector domain within the cell, which may have enzymatic activity or may undergo a conformational change detected by other proteins within the cell. Antibodies are protein components of an adaptive immune system whose main function is to bind antigens , or foreign substances in the body, and target them for destruction. Antibodies can be secreted into the extracellular environment or anchored in
6039-752: The cell's machinery through the process of protein turnover . A protein's lifespan is measured in terms of its half-life and covers a wide range. They can exist for minutes or years with an average lifespan of 1–2 days in mammalian cells. Abnormal or misfolded proteins are degraded more rapidly either due to being targeted for destruction or due to being unstable. Like other biological macromolecules such as polysaccharides and nucleic acids , proteins are essential parts of organisms and participate in virtually every process within cells . Many proteins are enzymes that catalyse biochemical reactions and are vital to metabolism . Proteins also have structural or mechanical functions, such as actin and myosin in muscle and
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#17328730795386138-450: The cell. Many ion channel proteins are specialized to select for only a particular ion; for example, potassium and sodium channels often discriminate for only one of the two ions. Structural proteins confer stiffness and rigidity to otherwise-fluid biological components. Most structural proteins are fibrous proteins ; for example, collagen and elastin are critical components of connective tissue such as cartilage , and keratin
6237-621: The chemical properties of their amino acids, others require the aid of molecular chaperones to fold into their native states. Biochemists often refer to four distinct aspects of a protein's structure: Proteins are not entirely rigid molecules. In addition to these levels of structure, proteins may shift between several related structures while they perform their functions. In the context of these functional rearrangements, these tertiary or quaternary structures are usually referred to as " conformations ", and transitions between them are called conformational changes. Such changes are often induced by
6336-441: The chief actors within the cell, said to be carrying out the duties specified by the information encoded in genes. With the exception of certain types of RNA , most other biological molecules are relatively inert elements upon which proteins act. Proteins make up half the dry weight of an Escherichia coli cell, whereas other macromolecules such as DNA and RNA make up only 3% and 20%, respectively. The set of proteins expressed in
6435-490: The construction of enormously complex signaling networks. As interactions between proteins are reversible, and depend heavily on the availability of different groups of partner proteins to form aggregates that are capable to carry out discrete sets of function, study of the interactions between specific proteins is a key to understand important aspects of cellular function, and ultimately the properties that distinguish particular cell types. The best-known role of proteins in
6534-408: The derivative unit kilodalton (kDa). The average size of a protein increases from Archaea to Bacteria to Eukaryote (283, 311, 438 residues and 31, 34, 49 kDa respectively) due to a bigger number of protein domains constituting proteins in higher organisms. For instance, yeast proteins are on average 466 amino acids long and 53 kDa in mass. The largest known proteins are the titins , a component of
6633-422: The development of the enzyme, leading to congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency. Gene conversion events involving the functional gene and the pseudogene account for many cases of steroid 21-hydroxylase deficiency. CAH is an autosomal recessive disorder . There are multiple forms of CAH, defined as classical and nonclassical forms based on the amount of enzyme function still present in
6732-553: The enzyme may cause congenital adrenal hyperplasia . Steroid 21-hydroxylase is a member of the cytochrome P450 family of monooxygenase enzymes that use an iron-containing heme cofactor to oxidize substrates. In humans, the enzyme is localized in endoplasmic reticulum membranes of cells in adrenal cortex , and is encoded by the CYP21A2 gene which is located near the CYP21A1P pseudogene that has high degree of sequence similarity. This similarity makes it difficult to analyze
6831-447: The erroneous conclusion that they might be composed of a single type of (very large) molecule. The term "protein" to describe these molecules was proposed by Mulder's associate Berzelius; protein is derived from the Greek word πρώτειος ( proteios ), meaning "primary", "in the lead", or "standing in front", + -in . Mulder went on to identify the products of protein degradation such as
6930-519: The functional gene, making it difficult to distinguish between them. The pseudogene can also recombine with the functional gene, creating hybrid genes that have features of both. This can result in false-positive or false-negative results when testing for SNPs in the CYP21A2 . The whole genome sequencing technology relies on breaking the DNA into small fragments, sequencing them, and then assembling them back together based on their overlaps. However, because of
7029-456: The gene at the molecular level, and sometimes leads to loss-of-function mutations of the gene due to intergenic exchange of DNA . 4Y8W ,%%s 2GEG 1589 13079 ENSG00000235134 ENSMUSG00000024365 P08686 Q08AG9 P03940 NM_000500 NM_001128590 NM_009995 NP_001122062.3 NP_034125 Steroid 21-hydroxylase in humans is encoded by the CYP21A2 gene that may be accompanied by one or several copies of
7128-427: The high homology and variability of the CYP21A2 and its pseudogene, the fragments cannot be mapped unambiguously to either copy of the gene. This can lead to errors or gaps in the assembly, or missing some variants that are present in the gene. Polymerase chain reaction (PCR) molecular diagnostics uses selective primers to amplify specific segments of the DNA sequence that are relevant for diagnosing or detecting
7227-404: The human genome. MHC class III genes are similar in humans, mouse, frog ( Xenopus tropicalis ), and gray short-tailed opossum , but not all genes are common. For example, human NCR3 , MIC and MCCD1 are absent in mouse. Human NCR3 and LST1 are absent in opossum. However, birds (chicken and quail) have only a single gene, which codes for a complement component gene (C4). In fishes,
7326-525: The late 1700s and early 1800s included gluten , plant albumin , gliadin , and legumin . Proteins were first described by the Dutch chemist Gerardus Johannes Mulder and named by the Swedish chemist Jöns Jacob Berzelius in 1838. Mulder carried out elemental analysis of common proteins and found that nearly all proteins had the same empirical formula , C 400 H 620 N 100 O 120 P 1 S 1 . He came to
7425-478: The major component of connective tissue, or keratin , the protein component of hair and nails. Membrane proteins often serve as receptors or provide channels for polar or charged molecules to pass through the cell membrane . A special case of intramolecular hydrogen bonds within proteins, poorly shielded from water attack and hence promoting their own dehydration , are called dehydrons . Many proteins are composed of several protein domains , i.e. segments of
7524-443: The mature mRNA, which is then used as a template for protein synthesis by the ribosome . In prokaryotes the mRNA may either be used as soon as it is produced, or be bound by a ribosome after having moved away from the nucleoid . In contrast, eukaryotes make mRNA in the cell nucleus and then translocate it across the nuclear membrane into the cytoplasm , where protein synthesis then takes place. The rate of protein synthesis
7623-405: The membranes of specialized B cells known as plasma cells . Whereas enzymes are limited in their binding affinity for their substrates by the necessity of conducting their reaction, antibodies have no such constraints. An antibody's binding affinity to its target is extraordinarily high. Many ligand transport proteins bind particular small biomolecules and transport them to other locations in
7722-496: The nobel prize in 1972, solidified the thermodynamic hypothesis of protein folding, according to which the folded form of a protein represents its free energy minimum. With the development of X-ray crystallography , it became possible to determine protein structures as well as their sequences. The first protein structures to be solved were hemoglobin by Max Perutz and myoglobin by John Kendrew , in 1958. The use of computers and increasing computing power also supported
7821-418: The nonfunctional pseudogene CYP21A1P , this pseudogene shares 98% of the exonic informational identity with the actual functional gene. Pseudogenes are common in genomes, and they originate as artifacts during the duplication process. Though often thought of as "junk DNA", research has shown that retaining these faulty copies can have a beneficial role, often providing regulation of their parent genes. In
7920-500: The order of 50,000 to 1 million. By contrast, eukaryotic cells are larger and thus contain much more protein. For instance, yeast cells have been estimated to contain about 50 million proteins and human cells on the order of 1 to 3 billion. The concentration of individual protein copies ranges from a few molecules per cell up to 20 million. Not all genes coding proteins are expressed in most cells and their number depends on, for example, cell type and external stimuli. For instance, of
8019-462: The parents, which is not always feasible or practical. Therefore, to analyze the CYP21A2 gene accurately, a more specialized and sensitive method is needed, such as targeted long-read sequencing , which can sequence longer DNA fragments and capture more information about the gene structure and variation. However, this method is not widely available or affordable for clinical use. Steroid 21-hydroxylase,
8118-535: The patient. The classical forms occur in approximately 1 in 10 000 to 1 in 20 000 births globally, and includes both the salt-wasting (excessive excretion of sodium via the urine causing hyponatremia and dehydration) and simple-virilizing forms. Complete loss of enzymatic activity causes the salt-wasting form. Variations in the structure of steroid 21-hydroxylase are related to the clinical severity of congenital adrenal hyperplasia. Cortisol and aldosterone deficits are associated with life-threatening sodium loss, as
8217-440: The physical and chemical properties, folding, stability, activity, and ultimately, the function of the proteins. Some proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors . Proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes . Once formed, proteins only exist for a certain period and are then degraded and recycled by
8316-424: The process of cell signaling and signal transduction . Some proteins, such as insulin , are extracellular proteins that transmit a signal from the cell in which they were synthesized to other cells in distant tissues . Others are membrane proteins that act as receptors whose main function is to bind a signaling molecule and induce a biochemical response in the cell. Many receptors have a binding site exposed on
8415-534: The protein or proteins of interest based on properties such as molecular weight, net charge and binding affinity. The level of purification can be monitored using various types of gel electrophoresis if the desired protein's molecular weight and isoelectric point are known, by spectroscopy if the protein has distinguishable spectroscopic features, or by enzyme assays if the protein has enzymatic activity. Additionally, proteins can be isolated according to their charge using electrofocusing . For natural proteins,
8514-427: The proteins in the cytoskeleton , which form a system of scaffolding that maintains cell shape. Other proteins are important in cell signaling, immune responses , cell adhesion , and the cell cycle . In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized . Digestion breaks the proteins down for metabolic use. Proteins have been studied and recognized since
8613-582: The same molecule, they can oligomerize to form fibrils; this process occurs often in structural proteins that consist of globular monomers that self-associate to form rigid fibers. Protein–protein interactions also regulate enzymatic activity, control progression through the cell cycle , and allow the assembly of large protein complexes that carry out many closely related reactions with a common biological function. Proteins can also bind to, or even be integrated into, cell membranes. The ability of binding partners to induce conformational changes in proteins allows
8712-573: The sample, allowing scientists to obtain more information and analyze larger structures. Computational protein structure prediction of small protein structural domains has also helped researchers to approach atomic-level resolution of protein structures. As of April 2024 , the Protein Data Bank contains 181,018 X-ray, 19,809 EM and 12,697 NMR protein structures. Proteins are primarily classified by sequence and structure, although other classifications are commonly used. Especially for enzymes
8811-430: The sequencing of complex proteins. In 1999, Roger Kornberg succeeded in sequencing the highly complex structure of RNA polymerase using high intensity X-rays from synchrotrons . Since then, cryo-electron microscopy (cryo-EM) of large macromolecular assemblies has been developed. Cryo-EM uses protein samples that are frozen rather than crystals, and beams of electrons rather than X-rays. It causes less damage to
8910-640: The signs and symptoms of the condition may include acne , hirsutism , male-pattern baldness, irregular menstruation, and infertility. Fewer studies have been published about males with NCCAH comparing to those about females, because males are generally asymptomatic. Males, however, may present with acne and early balding. While symptoms are usually diagnosed after puberty, children may present with premature adrenarche . Protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues . Proteins perform
9009-501: The steroid 21-hydroxylase can be found in all vertebrates . Cyp21 first emerged in chordates before the speciation between basal chordates and vertebrates. The sea lamprey , an early jawless fish species that originated over 500 million years ago, provides valuable insights into the evolution and emergence of Cyp21 . Sea lampreys lack the 11β-hydroxylase enzyme responsible for converting 11-deoxycortisol to cortisol as observed in mammals. Instead, they rely on 11-deoxycortisol,
9108-411: The steroids play roles in regulating sodium homeostasis . Simple-virilizing CAH patients (~1-2% enzyme function) maintain adequate sodium homeostasis, but exhibit other symptoms shared by the salt-wasting form, including accelerated growth in childhood and ambiguous genitalia in female neonates . The nonclassical form is the mildest condition, retaining about 20% to 50% of enzyme function. This form
9207-405: The substrate, and an even smaller fraction—three to four residues on average—that are directly involved in catalysis. The region of the enzyme that binds the substrate and contains the catalytic residues is known as the active site . Dirigent proteins are members of a class of proteins that dictate the stereochemistry of a compound synthesized by other enzymes. Many proteins are involved in
9306-706: The surrounding amino acids may determine the exact binding specificity). Many such motifs has been collected in the Eukaryotic Linear Motif (ELM) database. Topology of a protein describes the entanglement of the backbone and the arrangement of contacts within the folded chain. Two theoretical frameworks of knot theory and Circuit topology have been applied to characterise protein topology. Being able to describe protein topology opens up new pathways for protein engineering and pharmaceutical development, and adds to our understanding of protein misfolding diseases such as neuromuscular disorders and cancer. Proteins are
9405-400: The tRNA molecules with the correct amino acids. The growing polypeptide is often termed the nascent chain . Proteins are always biosynthesized from N-terminus to C-terminus . The size of a synthesized protein can be measured by the number of amino acids it contains and by its total molecular mass , which is normally reported in units of daltons (synonymous with atomic mass units ), or
9504-472: The tertiary structure of the protein, which defines the binding site pocket, and by the chemical properties of the surrounding amino acids' side chains. Protein binding can be extraordinarily tight and specific; for example, the ribonuclease inhibitor protein binds to human angiogenin with a sub-femtomolar dissociation constant (<10 M) but does not bind at all to its amphibian homolog onconase (> 1 M). Extremely minor chemical changes such as
9603-466: Was insulin , by Frederick Sanger , in 1949. Sanger correctly determined the amino acid sequence of insulin, thus conclusively demonstrating that proteins consisted of linear polymers of amino acids rather than branched chains, colloids , or cyclols . He won the Nobel Prize for this achievement in 1958. Christian Anfinsen 's studies of the oxidative folding process of ribonuclease A, for which he won
9702-429: Was first described in 1952. Studies of the human enzyme expressed in yeast initially classified 17-hydroxyprogesterone as the preferred substrate for steroid 21-hydroxylase, however, later analysis of the purified human enzyme found a lower K M and greater catalytic efficiency for progesterone over 17-hydroxyprogesterone. The catalytic efficiency of steroid 21-hydroxylase for conversion of progesterone in humans
9801-581: Was not fully appreciated until 1926, when James B. Sumner showed that the enzyme urease was in fact a protein. Linus Pauling is credited with the successful prediction of regular protein secondary structures based on hydrogen bonding , an idea first put forth by William Astbury in 1933. Later work by Walter Kauzmann on denaturation , based partly on previous studies by Kaj Linderstrøm-Lang , contributed an understanding of protein folding and structure mediated by hydrophobic interactions . The first protein to have its amino acid chain sequenced
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