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In biochemistry, a disulfide refers to a functional group with the structure R−S−S−R′. The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In biology, disulfide bridges formed between thiol groups in two cysteine residues are an important component of the secondary and tertiary structure of proteins. Persulfide usually refers to R−S−S−H compounds.
Post-translational modification (PTM) is the covalent process of changing proteins following protein biosynthesis. PTMs may involve enzymes or occur spontaneously. Proteins are created by ribosomes translating mRNA into polypeptide chains, which may then change to form the mature protein product. PTMs are important components in cell signalling, as for example when prohormones are converted to hormones.
Protein disulfide isomerase, or PDI, is an enzyme in the endoplasmic reticulum (ER) in eukaryotes and the periplasm of bacteria that catalyzes the formation and breakage of disulfide bonds between cysteine residues within proteins as they fold. This allows proteins to quickly find the correct arrangement of disulfide bonds in their fully folded state, and therefore the enzyme acts to catalyze protein folding.
Phalloidin belongs to a class of toxins called phallotoxins, which are found in the death cap mushroom (Amanita phalloides). It is a rigid bicyclic heptapeptide that is lethal after a few days when injected into the bloodstream. The major symptom of phalloidin poisoning is acute hunger due to the destruction of liver cells. It functions by binding and stabilizing filamentous actin (F-actin) and effectively prevents the depolymerization of actin fibers. Due to its tight and selective binding to F-actin, derivatives of phalloidin containing fluorescent tags are used widely in microscopy to visualize F-actin in biomedical research.
Cyclic nucleotide–gated ion channels or CNG channels are ion channels that function in response to the binding of cyclic nucleotides. CNG channels are nonselective cation channels that are found in the membranes of various tissue and cell types, and are significant in sensory transduction as well as cellular development. Their function can be the result of a combination of the binding of cyclic nucleotides and either a depolarization or a hyperpolarization event. Initially discovered in the cells that make up the retina of the eye, CNG channels have been found in many different cell types across both the animal and the plant kingdoms. CNG channels have a very complex structure with various subunits and domains that play a critical role in their function. CNG channels are significant in the function of various sensory pathways including vision and olfaction, as well as in other key cellular functions such as hormone release and chemotaxis. CNG channels have also been found to exist in prokaryotes, including many spirochaeta, though their precise role in bacterial physiology remains unknown.
Vitronectin is a glycoprotein of the hemopexin family which is synthesized and excreted by the liver, and abundantly found in serum, the extracellular matrix and bone. In humans it is encoded by the VTN gene.
Tissue transglutaminase is a 78-kDa, calcium-dependent enzyme of the protein-glutamine γ-glutamyltransferases family. Like other transglutaminases, it crosslinks proteins between an ε-amino group of a lysine residue and a γ-carboxamide group of glutamine residue, creating an inter- or intramolecular bond that is highly resistant to proteolysis. Aside from its crosslinking function, tTG catalyzes other types of reactions including deamidation, GTP-binding/hydrolyzing, and isopeptidase activities. Unlike other members of the transglutaminase family, tTG can be found both in the intracellular and the extracellular spaces of various types of tissues and is found in many different organs including the heart, the liver, and the small intestine. Intracellular tTG is abundant in the cytosol but smaller amounts can also be found in the nucleus and the mitochondria. Intracellular tTG is thought to play an important role in apoptosis. In the extracellular space, tTG binds to proteins of the extracellular matrix (ECM), binding particularly tightly to fibronectin. Extracellular tTG has been linked to cell adhesion, ECM stabilization, wound healing, receptor signaling, cellular proliferation, and cellular motility.
Peroxiredoxins are a ubiquitous family of antioxidant enzymes that also control cytokine-induced peroxide levels and thereby mediate signal transduction in mammalian cells. The family members in humans are PRDX1, PRDX2, PRDX3, PRDX4, PRDX5, and PRDX6. The physiological importance of peroxiredoxins is indicated by their relative abundance. Their function is the reduction of peroxides, specifically hydrogen peroxide, alkyl hydroperoxides, and peroxynitrite.
The transforming growth factor beta (TGF-β) superfamily is a large group of structurally related cell regulatory proteins that was named after its first member, TGF-β1, originally described in 1983. They interact with TGF-beta receptors.
Protein disulfide-isomerase A3 (PDIA3), also known as glucose-regulated protein, 58-kD (GRP58), is an isomerase enzyme. This protein localizes to the endoplasmic reticulum (ER) and interacts with lectin chaperones calreticulin and calnexin (CNX) to modulate folding of newly synthesized glycoproteins. It is thought that complexes of lectins and this protein mediate protein folding by promoting formation of disulfide bonds in their glycoprotein substrates.
Autotaxin, also known as ectonucleotide pyrophosphatase/phosphodiesterase family member 2, is an enzyme that in humans is encoded by the ENPP2 gene.
Discoidin domain is major protein domain of many blood coagulation factors.
Cathepsin L1 is a protein that in humans is encoded by the CTSL1 gene. The protein is a cysteine cathepsin, a lysosomal cysteine protease that plays a major role in intracellular protein catabolism.
Ectonucleotide pyrophosphatase/phosphodiesterase family member 1 is an enzyme that in humans is encoded by the ENPP1 gene.
Disulfide bond formation protein B (DsbB) is a protein component of the pathway that leads to disulfide bond formation in periplasmic proteins of Escherichia coli (P0A6M2) and other bacteria. In Bacillus subtilis it is known as BdbC (O32217).
DsbA is a bacterial thiol disulfide oxidoreductase (TDOR). DsbA is a key component of the Dsb family of enzymes. DsbA catalyzes intrachain disulfide bond formation as peptides emerge into the cell's periplasm.
Triflin is a cysteine-rich secretory protein (CRISP), which is excreted by the venom gland of the Habu snake. Triflin reduces high potassium-induced smooth muscle contraction, suggesting a blocking effect on L-type calcium channels.
In molecular biology, the amylin protein family or calcitonin/CGRP/IAPP protein family is a family of proteins, which includes the precursors of calcitonin/calcitonin gene-related peptide (CGRP), islet amyloid polypeptide (IAPP) and adrenomedullin.
Nucleotide pyrophosphatase/phosphodiesterase (NPP) is a class of dimeric enzymes that catalyze the hydrolysis of phosphate diester bonds. NPP belongs to the alkaline phosphatase (AP) superfamily of enzymes. Humans express seven known NPP isoforms, some of which prefer nucleotide substrates, some of which prefer phospholipid substrates, and others of which prefer substrates that have not yet been determined. In eukaryotes, most NPPs are located in the cell membrane and hydrolyze extracellular phosphate diesters to affect a wide variety of biological processes. Bacterial NPP is thought to localize to the periplasm.
Wasabi receptor toxin (WaTx) is the active component of the venom of the Australian black rock scorpion Urodacus manicatus. WaTx targets TRPA1, also known as the wasabi receptor or irritant receptor. WaTx is a cell-penetrating toxin that stabilizes the TRPA1 channel open state while reducing its Ca2+-permeability, thereby eliciting pain and pain hypersensitivity without the neurogenic inflammation that typically occurs in other animal toxins.
References
- ↑ Jenne D, Stanley KK (1987). "Nucleotide sequence and organization of the human S-protein gene: repeating peptide motifs in the "pexin" family and a model for their evolution". Biochemistry. 26 (21): 6735–6742. doi:10.1021/bi00395a024. PMID 2447940.
- ↑ Jenne D (1991). "Homology of placental protein 11 and pea seed albumin 2 with vitronectin". Biochem. Biophys. Res. Commun. 176 (3): 1000–1006. doi:10.1016/0006-291X(91)90381-G. PMID 1710108.
- ↑ Rebbe NF, Tong BD, Finley EM, Hickman S (1991). "Identification of nucleotide pyrophosphatase/alkaline phosphodiesterase I activity associated with the mouse plasma cell differentiation antigen PC-1". Proc. Natl. Acad. Sci. U.S.A. 88 (12): 5192–5196. Bibcode:1991PNAS...88.5192R. doi: 10.1073/pnas.88.12.5192 . PMC 51838 . PMID 1647027.
- ↑ Gijsbers R, Ceulemans H, Bollen M (2003). "Functional characterization of the non-catalytic ectodomains of the nucleotide pyrophosphatase/phosphodiesterase NPP1". Biochem. J. 371 (Pt 2): 321–330. doi:10.1042/BJ20021943. PMC 1223305 . PMID 12533192.
- ↑ Dyson HJ, Kamikubo Y, Kroon G, Curriden S, Neels JG, Churchill MJ, Dawson P, Jagielska A, Scheraga HA, Loskutoff DJ, De Guzman R, OBdziej S (2004). "Disulfide bonding arrangements in active forms of the somatomedin B domain of human vitronectin". Biochemistry. 43 (21): 6519–6534. doi:10.1021/bi049647c. PMID 15157085.
- ↑ Carrell RW, Zhou A, Read RJ, Huntington JA, Pannu NS (2003). "How vitronectin binds PAI-1 to modulate fibrinolysis and cell migration". Nat. Struct. Biol. 10 (7): 541–544. doi:10.1038/nsb943. PMID 12808446. S2CID 26086796.