1SJT

MINI-PROINSULIN, TWO CHAIN INSULIN ANALOG MUTANT: DES B30, HIS(B 10)ASP, PRO(B 28)ASP, NMR, 20 STRUCTURES

Summary for 1SJT

• Entry DOI: 10.2210/pdb1sjt/pdb
• Descriptor: PROINSULIN (2 entities in total)
• Functional Keywords: hormone, glucose metabolism, disease mutation, diabetes
• Biological source: Homo sapiens (human); More
• Cellular location: Secreted: P01308 P01308
• Total number of polymer chains: 2
• Total formula weight: 5711.46

Authors

Hua, Q.X.,Hu, S.Q.,Jia, W.H.,Chu, Y.C.,Burke, G.T.,Wang, S.H.,Katsoyannis, P.G.,Weiss, M.A. (deposition date: 1997-10-09, release date: 1998-03-18, Last modification date: 2024-10-30)

Primary citation

Hua, Q.X.,Hu, S.Q.,Jia, W.,Chu, Y.C.,Burke, G.T.,Wang, S.H.,Wang, R.Y.,Katsoyannis, P.G.,Weiss, M.A.
Mini-proinsulin and mini-IGF-I: homologous protein sequences encoding non-homologous structures.
J.Mol.Biol., 277:103-118, 1998

PubMed Abstract: Protein minimization highlights essential determinants of structure and function. Minimal models of proinsulin and insulin-like growth factor I contain homologous A and B domains as single-chain analogues. Such models (designated mini-proinsulin and mini-IGF-I) have attracted wide interest due to their native foldability but complete absence of biological activity. The crystal structure of mini-proinsulin, determined as a T3R3 hexamer, is similar to that of the native insulin hexamer. Here, we describe the solution structure of a monomeric mini-proinsulin under physiologic conditions and compare this structure to that of the corresponding two-chain analogue. The two proteins each contain substitutions in the B-chain (HisB10-->Asp and ProB28-->Asp) designed to destabilize self-association by electrostatic repulsion; the proteins differ by the presence or absence of a peptide bond between LysB29 and GlyA1. The structures are essentially identical, resembling in each case the T-state crystallographic protomer. Differences are observed near the site of cross-linking: the adjoining A1-A8 alpha-helix (variable among crystal structures) is less well-ordered in mini-proinsulin than in the two-chain variant. The single-chain analogue is not completely inactive: its affinity for the insulin receptor is 1500-fold lower than that of the two-chain analogue. Moreover, at saturating concentrations mini-proinsulin retains the ability to stimulate lipogenesis in adipocytes (native biological potency). These results suggest that a change in the conformation of insulin, as tethered by the B29-A1 peptide bond, optimizes affinity but is not integral to the mechanism of transmembrane signaling. Surprisingly, the tertiary structure of mini-proinsulin differs from that of mini-IGF-I (main-chain rms deviation 4.5 A) despite strict conservation of non-polar residues in their respective hydrophobic cores (side-chain rms deviation 4.9 A). Three-dimensional profile scores suggest that the two structures each provide acceptable templates for threading of insulin-like sequences. Mini-proinsulin and mini-IGF-I thus provide examples of homologous protein sequences encoding non-homologous structures.

PubMed: 9514738
DOI: 10.1006/jmbi.1997.1574

Experimental method

SOLUTION NMR