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90-459: 2VWF , 2W0Z , 5EXA , 5EWZ 9846 14389 ENSG00000033327 ENSMUSG00000004508 Q9UQC2 Q9Z1S8 NM_012296 NM_080491 NM_001162477 NM_010248 NP_036428 NP_536739 n/a GRB2-associated-binding protein 2 also known as GAB2 is a protein that in humans is encoded by the GAB2 gene . GAB2 is a docking protein with a conserved, folded PH domain attached to

180-516: 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

270-470: 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.

360-547: A PX3RX2KP motif in order to produce a regulatory signal. The activated GAB2 can now recruit SH2 domain-containing molecules, such as SHP2 or PI3K to activate signaling pathways. The p85 subunit of PI3K (or PIK3) possessed the SH2 domain required to be activated by GAB2. The activation of the PI3K signaling pathway produces increased amyloid production and microglia -mediated inflammation. The immunoglobulin receptor FceRI requires GAB2 as

450-576: A characteristic beta-barrel fold that consists of five or six β-strands arranged as two tightly packed anti-parallel β sheets . The linker regions may contain short helices. The SH3-type fold is an ancient fold found in eukaryotes as well as prokaryotes. The classical SH3 domain is usually found in proteins that interact with other proteins and mediate assembly of specific protein complexes, typically via binding to proline -rich peptides in their respective binding partner. Classical SH3 domains are restricted in humans to intracellular proteins, although

540-552: 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,

630-508: A core consensus motif R-x-x-K have been described. Examples are the C-terminal SH3 domains of adaptor proteins like Grb2 and Mona (a.k.a. Gads, Grap2, Grf40, GrpL etc.). Other SH3 binding motifs have emerged and are still emerging in the course of various molecular studies, highlighting the versatility of this domain. SH3 domain-mediated protein-protein interaction networks, i.e. , SH3 interactomes, revealed that worm SH3 interactome resembles

720-403: 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

810-834: 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

900-555: A folded N-terminal domain attached to an extended, disordered C-terminal tail rich in short linear motifs . LMDs are docking proteins that function as platforms mediating interaction between different signaling pathways and assisting with signal integration. The N-terminal is characterized by a Pleckstrin Homology (PH) domain that is the most highly conserved region between all members of the GAB family of proteins. ( GAB1 , GAB2, GAB3 and GAB4) GAB2

990-478: 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

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1080-502: A necessity for mast cells to activate PI3K receptor to create an allergic response. In a study of knockout mice lacking the GAB2 gene, subjects experienced impaired allergic reactions, including passive cutaneous and systemic anaphylaxis . PI3K is found to be mutated in most breast cancer subtypes. Sufficient GAB2 expression by these cancerous subtypes proves necessary in order to sustain a cancerous phenotype. The erythropoietin hormone (Epo)

1170-410: 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

1260-500: 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

1350-411: 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

1440-539: 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

1530-486: 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

1620-487: A role in the pathogenesis of Alzheimer's disease via its interaction with tau and amyloid precursor proteins. GAB2 may prevent neuronal tangle formation characteristic of LOAD by reducing phosphorylation of tau protein via the activation of the PI3K signaling pathway, which activates Akt . Akt inactivates Gsk3 , which is responsible for tau phosphorylation. Mutations in GAB2 could affect Gsk3-dependent phosphorylation of tau and

1710-406: 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 "),

1800-481: A site for multiple phosphorylation of tyrosine kinases. It acts as a docking station for the Src homology 2( SH2 ) domain that is contained in the adaptor protein families Crk , Grb2 , and Nck . These adaptor proteins then couple to enzymes to amplify different cellular signals. GAB2 may also bind directly to SH2-containing enzymes, such as PI3K , to produce such signals. GAB2 has been shown to interact with: Through

1890-432: 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

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1980-451: 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

2070-441: 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

2160-432: 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

2250-547: Is an Intrinsically disordered protein , meaning that beyond the folded N-terminal region, the C-terminal region extends out into the cytoplasm with little or no secondary structure . The disordered region of the protein however may not be as disordered as was initially expected, as sequencing has revealed significant similarity between the "disordered" regions of GAB orthologs in different species. The PH domain of GAB2 recognizes phosphatidylinositol 3,4,5-triphosphate (PIP3) in

2340-463: 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. SH3 domain The SH3 domain has

2430-628: 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

2520-469: 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"

2610-461: 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

2700-404: 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

2790-457: Is required for the association of CRKL and GAB2. This leads to the activation of c-Jun N-terminal kinase( JNK ) as part of the JNK signaling pathway. Upon stimulation by growth hormone , insulin , epidermal growth factor (EFG), etc., the GAB2 protein can be recruited from the cytoplasm to the cell membrane, where it forms a complex with Grb2 and SHC. The interaction between GAB2 and Grb2 requires

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2880-553: Is responsible for the regulation and proliferation of erythrocytes . Epo is able to self phosphorylate, which causes recruitment of SH2 proteins. An activated complex of GAB2, SHC, and SHP2 is required for binding of Phospholipase C gamma 2 (PLCG2) through its SH2 domain, which activates PIP3 . Protein tyrosine phosphatase non-receptor 11 (PTPN11) interaction with GAB2 is part of the Ras pathway. Mutations found in PTPN11 cause disruption in

2970-475: Is the activation of the ERK / MAPK pathway. There are also, however, other pathways that are activated by this interaction such as the pathways c-Kit-induced Rac activation and β1-integrin. PI3K activation by GAB2 promotes cell growth. The effects of all the pathways activated by GAB proteins are not known, but it is easy to see that amplification of signal can progress quickly and these proteins can have large effects on

3060-532: 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

3150-888: The Bcr-Abl complex and is instrumental in maintaining the oncogenic properties of the complex. The Grb2/GAB2 complex is recruited to phosphorylated Y177 of the Bcr-Abl complex leading to Bcr-Abl-mediated transformation and leukemogenesis. GAB2 also plays a role in juvenile myelomonocytic leukemia (JMML). Studies have shown the protein's involvement in the disease via the Ras pathway. In addition, GAB2 appears to play an important role in PTPN11 mutations associated with JMML. Protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues . Proteins perform

3240-486: 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

3330-644: 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

3420-645: 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,

3510-493: 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

3600-562: 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

3690-498: 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 )

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3780-516: 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

3870-410: The PI3K signaling pathway, PI3K activates the serine/threonine protein kinase (AKT), which in turn through phosphorylation inactivates GSK3 . This in turn causes the phosphorylation of tau and amyloid production. CT10 regulator of kinase (Crk) is also known as the breast cancer anti-oestrogen resistance protein. It plays a role in both fibroblast formation and breast cancer. The YXXP binding motif

3960-709: 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

4050-405: 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

4140-595: 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

4230-531: 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

4320-574: 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 ,

4410-480: The binding to GAB2, which in turn impairs correct cellular growth. Thirty-five percent of patients diagnosed with JMML show activating mutations in PTPN11. GC-GAP is part of the Rho GTP-ase activating protein family (RICS). It contains a highly proline-rich motifs that allow favorable interactions with GAB2. GC-GAP is responsible for the proliferation of astroglioma cells. The interaction between GAB2 and Grb2 at

4500-570: 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

4590-558: 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

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4680-559: The cell membrane recruits another adaptor protein, the Src homology domain-containing transforming protein 1 (SHC1), before being able to recruit SH2 domain-containing molecules. Ten SNPs of GAB2 have been associated with late-onset Alzheimer's disease (LOAD). However, this association is found only in APOE ε4 carriers. In LOAD brains, GAB2 is overexpressed in neurons, tangle-bearing neurons, and dystrophic neuritis . GAB2 has been indicated in playing

4770-436: 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

4860-752: 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

4950-450: 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

5040-621: 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

5130-441: 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

5220-490: 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

5310-408: 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

5400-502: The disordered domain is looped back to connect to the N-terminal, structured region several times to make the protein more compact. This would assist in promoting interactions between molecules bound to GAB and resisting degradation. GAB2 mediates the interactions between receptor tyrosine kinases (RTK) or non-RTK receptors, such as G protein coupled receptors, cytokine receptors , multichain immune recognition receptors and integrins , and

5490-447: 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

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5580-435: The first steps in these signaling pathways. GAB2 has been shown to be important in physiological functions such as growth in bone marrow and cardiac function. GAB2 has also been associated with many diseases including leukemia and Alzheimer's disease . GAB proteins were one of the first docking proteins identified in the mammalian signal transduction pathway. GAB2 along with many other adaptor, scaffold, and docking proteins,

5670-601: The formation of neurofibrillary tangles . Interactions between GAB2-Grb2 and APP are enhanced in AD brains, suggesting an involvement of this coupling in the neuropathogenesis of AD. GAB2 has been linked to the oncogenesis of many cancers including colon, gastric, breast, and ovarian cancer. Studies suggest that GAB2 is used to amplify the signal of many RTKs implicated in breast cancer development and progression. GAB2 has been particularly characterized for its role in leukemia . In chronic myelogenous leukemia (CML), GAB2 interacts with

5760-525: 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

5850-478: 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

5940-443: 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

6030-471: The membrane and a large disordered region, which hosts interactions with signaling molecules. It is a member of the GAB/DOS family localized on the internal membrane of the cell. It mediates the interaction between receptor tyrosine kinases (RTKs) and non-RTK receptors serving as the gateway into the cell for activation of SHP2 , Phosphatidylinositol 3-kinase (PI3K), Grb2 , ERK , and AKT and acting as one of

6120-476: The membrane and is responsible for localizing the GAB protein on the intracellular surface of the membrane and in regions where the cell contacts another cell. Some evidence also suggests that the PH domain plays a role in some signal regulation as well. Adjacent to the PH domain is a central, proline-rich domain that contains many PXXP motifs for binding to the SH3 domains of signaling molecules such as Grb2 (from which

6210-405: 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

6300-580: The molecules of the intracellular signaling pathways. By providing a platform to host a wide array of interactions from extracellular inputs to intracellular pathways, GAB proteins can act as a gatekeeper to the cell, modulating and integrating signals as they pass them along, to control the functional state within the cell. Mutagenesis and Binding assays have helped to identify which molecules and what pathways are downstream of GAB2. The two main pathways of GAB proteins are SHP2 and PI3K. GAB protein binding to SHP2 molecules acts as an activator whose main effect

6390-466: The name "Grb2-associated binding" protein, GAB, comes). It is hypothesized that binding sites in this region may be used in indirect mechanisms pairing the GAB2 protein to receptor tyrosine kinases . It is on the C-terminal tail that the various conserved protein binding motifs and phosphorylation sites of GAB2 are found. GAB2 binds to the SH2 domains of such signaling molecules as SHP2 and PI3K . By binding to

6480-496: 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

6570-500: 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

6660-420: The p85 subunit of PI3K, and continuing this signaling pathway GAB provides positive feedback for the creation of PIP3, produced as a result of the PI3K pathway, which binds to GAB2 in the membrane and promotes activation of more PI3Ks. Discovery of multiple binding sites in GAB proteins has led to the N-terminal folding nucleation (NFN) hypothesis for the structure of the disordered region. This theory suggests that

6750-440: 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

6840-424: 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

6930-534: 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,

7020-427: 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

7110-582: 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

7200-573: 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

7290-430: 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

7380-482: The small human MIA family of extracellular proteins also contain a domain with an SH3-like fold. Many SH3-binding epitopes of proteins have a consensus sequence that can be represented as a regular expression or Short linear motif : with 1 and 4 being aliphatic amino acids, 2 and 5 always and 3 sometimes being proline. The sequence binds to the hydrophobic pocket of the SH3 domain. More recently, SH3 domains that bind to

7470-512: The state of the cell. While not lethal, GAB2 deficient knockout mice do exhibit phenotypic side-effects. These include weak allergic reactions, reduced mast cell growth in bone marrow and osteopetrosis . Knockout mice have also been used to show the importance of GAB2 in maintenance of cardiac function. A paracrine factor, NRG1 β, utilizes GAB2 to activate the ERK and AKT pathways in the heart to produce angiopoietin 1. The C-terminal tail of GAB2 acts as

7560-405: 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

7650-706: 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

7740-400: 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

7830-472: 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

7920-466: 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

8010-418: Was discovered in the mid-1990s during the isolation and cloning of protein tyrosine kinase substrates and association partners. GAB2 was initially discovered as a binding protein and substrate of protein tyrosine phosphatase Shp2/PTPN11. Two other groups later cloned GAB2 by searching DNA database for protein with sequence homology to GAB1. GAB2 is a large multi-site docking protein (LMD) of about 100kD that has

8100-581: 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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