Proinsulin - wikipedia Proinsulin insulin Insulin undergoes extensive posttranslational modification along the production pathway. Production and secretion are largely independent ; prepared insulin is stored awaiting secretion. Both C - peptide and mature insulin are biologically active. Cell components and proteins in this image are not to scale. Identifiers Symbol INS Entrez 3630 HUGO 6081 OMIM 176730 RefSeq NM_000207 UniProt P01308 Other data Locus Chr. 11 p15. 5 Proinsulin is the prohormone precursor to insulin made in the beta cells of the islets of Langerhans, specialized regions of the pancreas. In humans, proinsulin is encoded by the INS gene. The islets of Langerhans only secrete between 1 % and 3 % of proinsulin intact. However, because proinsulin has a longer half life than insulin, it can account for anywhere from 5 -- 30 % of the insulin - like structures circulating in the blood. There are higher concentrations of proinsulin after meals and lower levels when a person is fasting. Additionally, while proinsulin and insulin have structural differences, proinsulin does demonstrate some affinity for the insulin receptor. Due to the relative similarities in structure, proinsulin can produce between 5 % and 10 % of the metabolic activity similarly induced by insulin. Proinsulin is the final single chain protein structure secreted by cells before cleavage into mature insulin. Proinsulin was discovered by Professor Donald F. Steiner of the University of Chicago in 1967. Contents 1 Structure 2 Synthesis and Post-translational Modification 3 Immunogenicity 4 Medical Relevance 4.1 Diabetes Mellitus 4.2 Neonatal Diabetes Mellitus 5 See also 6 References Structure Proinsulin is made up of 81 residues and formed by three distinct chains. The A chain, B, chain, and the area connecting the two named the C peptide. The correct structure of proinsulin is crucial for the correct folding of mature insulin, as the placement of the C peptide sets the molecule up to create correctly positioned disulfide bonds in and between the A and B chains. There are three disulfide bonds that are necessary for mature insulin to be the correct structure. Two of these disulfide bonds are between the A and B chains, and one is an intra-A chain bond. The disulfide bonds occur between the seventh residues of the A and B chain, the 19th residue of the A chain and the 20th residue of the B chain, and the 6th and 11th residues of the A chain. The C peptide is between the A and B chains of proinsulin. The connection between the A chain and C peptide is much more stable than the junction between the C peptide and B chain, with alpha helical features being exhibited near the C peptide - A chain connection. The C peptide - A chain junction occurs between residues 64 and 65 of proinsulin. These are lysine and arginine molecules, respectively. The C peptide - B chain connection is between two arginine residues at positions 31 and 32 of proinsulin. There is conservation of much of the structure of proinsulin among mammalian species, with much of the residue changes seen from one species to another present in the C peptide. That said, the residues of the C peptide that are conserved across species interact with similarly conserved residues on the A and B chains. Thus, it is hypothesized that these conserved residues are important for the functionality of mature insulin. Synthesis and posttranslational modification Proinsulin is synthesized on membrane associated ribosomes found on the rough endoplasmic reticulum, where it is folded and its disulfide bonds are oxidized. It is then transported to the Golgi apparatus where it is packaged into secretory vesicles, and where it is processed by a series of proteases to form mature insulin. Mature insulin has 35 fewer amino acids ; 4 are removed altogether, and the remaining 31 form the C - peptide. The C - peptide is abstracted from the center of the proinsulin sequence ; the two other ends ( the B chain and A chain ) remain connected by disulfide bonds. The post translational modification of proinsulin to mature insulin only occurs in the beta cells of the islets of Langerhans. When proinsulin is transported through the Golgi apparatus the C - peptide is cleaved. This cleavage occurs with the aid of two endoproteases. Type I endoproteases, PC1 and PC3, disrupt the C peptide - B chain connection. PC2, a type II endoprotease, cleaves the C peptide - A chain bond. The resulting molecule, now mature insulin, is stored as a hexamer in secretory vesicles and is stabilized with Z n 2 + ( displaystyle Zn ^ ( 2 + ) ) molecules until it is secreted. Immunogenicity When insulin was originally purified from bovine or porcine pancreata, all the proinsulin was not fully removed. When some people used these insulins, the proinsulin may have caused the body to react with a rash, to resist the insulin, or even to make dents or lumps in the skin at the place where the insulin was injected. This can be described as an iatrogenic injury due to slight differences between the proinsulin of different species. Since the late 1970s, when highly purified porcine insulin was introduced, and the level of insulin purity reached 99 %, this ceased to be a significant clinical issue. It should also be noted that in respect of their influence on insulin pharmacokinetics, moderate concentrations of certain insulin antibodies may, in fact, be of positive advantage to all diabetics without endogenous insulin secretion ( e.g. people with type 1 diabetes ) because insulin binding antibodies effectively increase the insulin 's clearance rate and distribution space and therefore helps to prolong its pharmacological and biological half lives. Medical relevance Historically, the focus of many insulin related metabolic diseases has focused on mature insulin. However, in recent years the importance of studying the structure and function of proinsulin in relation to these diseases has become increasingly clear. Diabetes mellitus Increased levels of proinsulin in the circulatory system relative to mature insulin concentrations can indicate impending insulin resistance and the development of type 2 diabetes. Additional problems with proinsulin that can lead to diabetes include mutations in the number of cysteines present, which could affect correct folding. If the mutation causes only a mild change it could simply stress the endoplasmic reticulum 's ability to properly fold the protein. This stress, after a while, would lead to a decrease in the number of β - cells producing mature insulin, and would then lead to diabetes mellitus. Neonatal diabetes mellitus Postnatal proinsulin is crucial for metabolic regulation. However, proinsulin in neonates is important for normal development of the nerves of the eye, development of the heart, and general survival of embryonic cells. Regulation of the concentration of proinsulin during embryonic development is crucial, as too much or too little of the peptide can cause defects and death of the fetus. Thus far in the study of neonatal diabetes mellitus, only amino acid change mutations found in the B domain lead to the disease. See also insulin preproinsulin signal peptide signal peptide peptidase proprotein convertase 1 ( PC1 ) proprotein convertase 2 ( PC2 ) References Jump up ^ `` Entrez Gene : INS insulin ''. Jump up ^ Bell GI, Pictet RL, Rutter WJ, Cordell B, Tischer E, Goodman HM ( March 1980 ). `` Sequence of the human insulin gene ''. Nature. 284 ( 5751 ) : 26 -- 32. doi : 10.1038 / 284026a0. PMID 6243748. ^ Jump up to : `` Interpretation for 80908 Proinsulin, Plasma ''. www.mayomedicallaboratories.com. Retrieved 2017 - 03 - 09. Jump up ^ Hernandez - Sanchez, Catalina ; et al. ( 1995 ). `` Autocrine / paracrine role of insulin - related growth factors in neurogenesis : Local expression and effects on cell proliferation and differentiation in retina ''. Physiology. 92 : 9834 -- 9838. doi : 10.1073 / pnas. 92.21. 9834 -- via PNAS. CS1 maint : Explicit use of et al. ( link ) Jump up ^ Philipson, Louis ; et al. ( 2015 ). `` Donald F. Steiner MD, 1930 -- 2014 : Discoverer of proinsulin '' ( PDF ). Retrospective. 112 : 940 -- 941. doi : 10.1073 / pnas. 1423774112 -- via PNAS. CS1 maint : Explicit use of et al. ( link ) ^ Jump up to : Nolan, Chris ; Margoliash, E. ; Peterson, James D. ; Steiner, Donald F. ( 1971 - 05 - 10 ). `` The Structure of Bovine Proinsulin ''. Journal of Biological Chemistry. 246 ( 9 ) : 2780 -- 2795. ISSN 0021 - 9258. PMID 4928892. ^ Jump up to : Snell, C.R. ; Smyth, D.G. ( 1975 - 08 - 25 ). `` Proinsulin : a proposed three - dimensional structure ''. Journal of Biological Chemistry. 250 ( 16 ) : 6291 -- 6295. ISSN 0021 - 9258. PMID 808541. ^ Jump up to : Weiss, Michael A. ( 2009 - 07 - 17 ). `` Proinsulin and the Genetics of Diabetes Mellitus ''. Journal of Biological Chemistry. 284 ( 29 ) : 19159 -- 19163. doi : 10.1074 / jbc. R109. 009936. ISSN 0021 - 9258. PMC 2740536. PMID 19395706. ^ Jump up to : Yang, Yanwu ; et al. ( 2010 ). `` Solution Structure of Proinsulin : Connecting domain flexibility and prohormone processing '' ( PDF ). The Journal of Biological Chemistry. 285 : 7847 -- 7851. doi : 10.1074 / jbc. c109. 084921 -- via JBC. CS1 maint : Explicit use of et al. ( link ) Jump up ^ Bell, G.I. ; et al. ( 1980 ). `` Sequence of the human insulin gene ''. Nature. 284 : 26. doi : 10.1038 / 284026a0. PMID 6243748. CS1 maint : Explicit use of et al. ( link ) Jump up ^ Groskreutz, Debyra ( 1993 ). `` Genetically Engineered Proinsulin Constitutively Processed and Secreted as Mature, Active Insulin '' ( PDF ). The Journal of Biological Chemistry. 8 : 6241 -- 6245 -- via JBC. ^ Jump up to : Kaufmann, Jocelyn ; et al. ( 1995 ). `` Sequence requirements for proinsulin processing at the B - chain / C - peptide junction '' ( PDF ). Biochemistry. 310 : 869 -- 874. doi : 10.1042 / bj3100869. PMC 1135976. PMID 7575420. CS1 maint : Explicit use of et al. ( link ) Jump up ^ Wilson RM, Douglas CA, Tattersall RB, Reeves WG ( September 1985 ). `` Immunogenicity of highly purified bovine insulin : a comparison with conventional bovine and highly purified human insulins ''. Diabetologia. 28 ( 9 ) : 667 -- 70. doi : 10.1007 / BF00291973. PMID 3905477. Jump up ^ Tanyolac S, Goldfine ID, Kroon L. `` Insulin Pharmacology, Type of Regimens and Adjustments ''. Endotext.com. Retrieved 2011 - 03 - 18. Jump up ^ Home PD, Alberti KG ( November 1982 ). `` The new insulins. Their characteristics and clinical indications ''. Drugs. 24 ( 5 ) : 401 -- 13. doi : 10.2165 / 00003495 - 198224050 - 00003. PMID 6756879. Jump up ^ Gray RS, Cowan P, di Mario U, Elton RA, Clarke BF, Duncan LJ ( June 1985 ). `` Influence of insulin antibodies on pharmacokinetics and bioavailability of recombinant human and highly purified beef insulins in insulin dependent diabetics ''. Br Med J ( Clin Res Ed ). 290 ( 6483 ) : 1687 -- 91. doi : 10.1136 / bmj. 290.6483. 1687. PMC 1416075. PMID 3924216. Jump up ^ Mykkänen, Leena ; Haffner, Steven M. ; Hales, C. Nick ; Rönnemaa, Tapani ; Laakso, Markku ( 1997 - 12 - 01 ). `` The Relation of Proinsulin, Insulin, and Proinsulin - to - Insulin Ratio to Insulin Sensitivity and Acute Insulin Response in Normoglycemic Subjects ''. Diabetes. 46 ( 12 ) : 1990 -- 1995. doi : 10.2337 / diab. 46.12. 1990. ISSN 0012 - 1797. PMID 9392485. ^ Jump up to : Hernández - Sánchez, C. ; Mansilla, A. ; de la Rosa, E.J. ; de Pablo, F. ( 2006 - 06 - 01 ). `` Proinsulin in development : New roles for an ancient prohormone ''. Diabetologia. 49 ( 6 ) : 1142 -- 1150. doi : 10.1007 / s00125 - 006 - 0232 - 5. ISSN 0012 - 186X. PMID 16596360. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Proinsulin&oldid=830182359 '' Categories : Genes on human chromosome 11 Peptides Diabetes Hidden categories : CS1 maint : Explicit use of et al. Wikipedia articles needing clarification from August 2009 Talk Contents About Wikipedia Deutsch Español Italiano עברית Polski Русский Українська Edit links This page was last edited on 13 March 2018, at 07 : 46. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: mention the chemical change that proinsulin undergo to be able to act as mature insulin
Answer: post translational modification