Protein disulfide-isomerase, also known as the beta-subunit of prolyl 4-hydroxylase (P4HB), is an enzyme that in humans encoded by the P4HBgene. The human P4HB gene is localized in chromosome 17q25.[1][2][3][4] Unlike other prolyl 4-hydroxylase family proteins, this protein is multifunctional and acts as an oxidoreductase for disulfide formation, breakage, and isomerization.[5] The activity of P4HB is tightly regulated. Both dimer dissociation and substrate binding are likely to enhance its enzymatic activity during the catalysis process.[6][7]
P4HB has four thioredoxin domains (a, b, b’, and a’), with two CGHC active sites in the a and a’ domains. In both the reduced and oxidized state, these domains are arranged as a horseshoe shape. In reduced P4HB, domains a, b, and b' are in the same plane, while domain a' twists out at an ∼45° angle. When oxidized, the four domains stay in the same plane, and the distance between the active sites is larger than that in the reduced state. The oxidized form also exposes more hydrophobic areas and possesses a larger cleft to facilitate substrate binding.[8][9] P4HB has been shown to dimerize in vivo via noncatalytic bb' domains. Formation of dimer blocks substrate-binding site and inhibits P4HB’s activity.[10]
Function
This gene encodes the beta subunit of prolyl 4-hydroxylase, a highly abundant multifunctional enzyme that belongs to the protein disulfide isomerase family. When present as a tetramer consisting of two alpha and two beta subunits, this enzyme is involved in hydroxylation of prolyl residues in preprocollagen. This enzyme is also a disulfide isomerase containing two thioredoxin domains that catalyze the formation, breakage and rearrangement of disulfide bonds. Other known functions include its ability to act as a chaperone that inhibits aggregation of misfolded proteins in a concentration-dependent manner, its ability to bind thyroid hormone, its role in both the influx and efflux of S-nitrosothiol-bound nitric oxide, and its function as a subunit of the microsomal triglyceride transfer protein complex.[2]
↑Shoulders CC, Brett DJ, Bayliss JD, Narcisi TM, Jarmuz A, Grantham TT, Leoni PR, Bhattacharya S, Pease RJ, Cullen PM (December 1993). "Abetalipoproteinemia is caused by defects of the gene encoding the 97 kDa subunit of a microsomal triglyceride transfer protein". Human Molecular Genetics. 2 (12): 2109–16. doi:10.1093/hmg/2.12.2109. PMID8111381.
↑Pajunen L, Jones TA, Goddard A, Sheer D, Solomon E, Pihlajaniemi T, Kivirikko KI (1991-01-01). "Regional assignment of the human gene coding for a multifunctional polypeptide (P4HB) acting as the beta-subunit of prolyl 4-hydroxylase and the enzyme protein disulfide isomerase to 17q25". Cytogenetics and Cell Genetics. 56 (3–4): 165–8. doi:10.1159/000133078. PMID1647289.
↑Winter J, Klappa P, Freedman RB, Lilie H, Rudolph R (January 2002). "Catalytic activity and chaperone function of human protein-disulfide isomerase are required for the efficient refolding of proinsulin". The Journal of Biological Chemistry. 277 (1): 310–7. doi:10.1074/jbc.M107832200. PMID11694508.
↑Tian G, Xiang S, Noiva R, Lennarz WJ, Schindelin H (January 2006). "The crystal structure of yeast protein disulfide isomerase suggests cooperativity between its active sites". Cell. 124 (1): 61–73. doi:10.1016/j.cell.2005.10.044. PMID16413482.
↑Wang C, Li W, Ren J, Fang J, Ke H, Gong W, Feng W, Wang CC (July 2013). "Structural insights into the redox-regulated dynamic conformations of human protein disulfide isomerase". Antioxidants & Redox Signaling. 19 (1): 36–45. doi:10.1089/ars.2012.4630. PMID22657537.
↑Atkin JD, Farg MA, Walker AK, McLean C, Tomas D, Horne MK (June 2008). "Endoplasmic reticulum stress and induction of the unfolded protein response in human sporadic amyotrophic lateral sclerosis". Neurobiology of Disease. 30 (3): 400–7. doi:10.1016/j.nbd.2008.02.009. PMID18440237.
↑Walker AK, Farg MA, Bye CR, McLean CA, Horne MK, Atkin JD (January 2010). "Protein disulphide isomerase protects against protein aggregation and is S-nitrosylated in amyotrophic lateral sclerosis". Brain. 133 (Pt 1): 105–16. doi:10.1093/brain/awp267. PMID19903735.
↑Uehara T, Nakamura T, Yao D, Shi ZQ, Gu Z, Ma Y, Masliah E, Nomura Y, Lipton SA (May 2006). "S-nitrosylated protein-disulphide isomerase links protein misfolding to neurodegeneration". Nature. 441 (7092): 513–7. doi:10.1038/nature04782. PMID16724068.
↑Ko HS, Uehara T, Nomura Y (September 2002). "Role of ubiquilin associated with protein-disulfide isomerase in the endoplasmic reticulum in stress-induced apoptotic cell death". The Journal of Biological Chemistry. 277 (38): 35386–92. doi:10.1074/jbc.M203412200. PMID12095988.
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