| Contribution of residue B5 to the folding and function of insulin and IGF-I: constraints and fine-tuning in the evolution of a protein family. | |
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MedLine Citation:
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PMID: 19959476 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Proinsulin exhibits a single structure, whereas insulin-like growth factors refold as two disulfide isomers in equilibrium. Native insulin-related growth factor (IGF)-I has canonical cystines (A6-A11, A7-B7, and A20-B19) maintained by IGF-binding proteins; IGF-swap has alternative pairing (A7-A11, A6-B7, and A20-B19) and impaired activity. Studies of mini-domain models suggest that residue B5 (His in insulin and Thr in IGFs) governs the ambiguity or uniqueness of disulfide pairing. Residue B5, a site of mutation in proinsulin causing neonatal diabetes, is thus of broad biophysical interest. Here, we characterize reciprocal B5 substitutions in the two proteins. In insulin, His(B5) --> Thr markedly destabilizes the hormone (DeltaDeltaG(u) 2.0 +/- 0.2 kcal/mol), impairs chain combination, and blocks cellular secretion of proinsulin. The reciprocal IGF-I substitution Thr(B5) --> His (residue 4) specifies a unique structure with native (1)H NMR signature. Chemical shifts and nuclear Overhauser effects are similar to those of native IGF-I. Whereas wild-type IGF-I undergoes thiol-catalyzed disulfide exchange to yield IGF-swap, His(B5)-IGF-I retains canonical pairing. Chemical denaturation studies indicate that His(B5) does not significantly enhance thermodynamic stability (DeltaDeltaG(u) 0.2 +/- 0.2 kcal/mol), implying that the substitution favors canonical pairing by destabilizing competing folds. Whereas the activity of Thr(B5)-insulin is decreased 5-fold, His(B5)-IGF-I exhibits 2-fold increased affinity for the IGF receptor and augmented post-receptor signaling. We propose that conservation of Thr(B5) in IGF-I, rescued from structural ambiguity by IGF-binding proteins, reflects fine-tuning of signal transduction. In contrast, the conservation of His(B5) in insulin highlights its critical role in insulin biosynthesis. |
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Authors:
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Youhei Sohma; Qing-xin Hua; Ming Liu; Nelson B Phillips; Shi-Quan Hu; Jonathan Whittaker; Linda J Whittaker; Aubree Ng; Charles T Roberts; Peter Arvan; Stephen B H Kent; Michael A Weiss |
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Publication Detail:
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Type: Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S. Date: 2009-12-03 |
Journal Detail:
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Title: The Journal of biological chemistry Volume: 285 ISSN: 1083-351X ISO Abbreviation: J. Biol. Chem. Publication Date: 2010 Feb |
Date Detail:
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Created Date: 2010-02-08 Completed Date: 2010-05-11 Revised Date: 2012-04-05 |
Medline Journal Info:
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Nlm Unique ID: 2985121R Medline TA: J Biol Chem Country: United States |
Other Details:
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Languages: eng Pagination: 5040-55 Citation Subset: IM |
Affiliation:
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Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, USA. |
Export Citation:
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APA/MLA Format Download EndNote Download BibTex |
| MeSH Terms | |
Descriptor/Qualifier:
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Animals Cell Line Circular Dichroism Disulfides Glycosylation Humans Insulin / chemical synthesis, chemistry*, pharmacology* Insulin-Like Growth Factor I / chemical synthesis, chemistry*, pharmacology* Magnetic Resonance Spectroscopy Mice Phosphorylation / drug effects Proinsulin / biosynthesis, genetics, metabolism Protein Folding Protein Stability Signal Transduction / drug effects Structure-Activity Relationship |
| Grant Support | |
ID/Acronym/Agency:
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DK48280/DK/NIDDK NIH HHS; R01 DK040949-11/DK/NIDDK NIH HHS; R01 DK069764/DK/NIDDK NIH HHS; R01 DK069764-01/DK/NIDDK NIH HHS; R01 DK40949/DK/NIDDK NIH HHS |
| Chemical | |
Reg. No./Substance:
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0/Disulfides; 0/Insulin; 67763-96-6/Insulin-Like Growth Factor I; 9035-68-1/Proinsulin |
| Comments/Corrections | |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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