The landscape paradigm of protein folding can enable preferred pathways on a funnel-like energy surface. Hierarchical preferences may be manifest as a nonrandom pathway of disulfide pairing. Stepwise stabilization of structural subdomains among on-pathway intermediates is proposed to underlie the disulfide pathway of proinsulin and related molecules. Here, effects of pairwise serine substitution of insulin's exposed interchain disulfide bridge (Cys(A7)-Cys(B7)) are characterized as a model of a late intermediate. Untethering cystine A7-B7 in an engineered monomer causes significantly more marked decreases in the thermodynamic stability and extent of folding than occur on pairwise substitution of internal cystine A6-A11 [Weiss, M. A., Hua, Q. X., Jia, W., Chu, Y. C., Wang, R. Y., and Katsoyannis, P. G. (2000) Biochemistry 39, 15429-15440]. Although substantially disordered and without significant biological activity, the untethered analogue contains a molten subdomain comprising cystine A20-B19 and a native-like cluster of hydrophobic side chains. Remarkably, A and B chains make unequal contributions to this folded moiety; the B chain retains native-like supersecondary structure, whereas the A chain is largely disordered. These observations suggest that the B subdomain provides a template to guide folding of the A chain. Stepwise organization of insulin-like molecules supports a hierarchic view of protein folding. Study holds ProTherm entries: 12271 Extra Details: funnel-like energy surface; disulfide pathway; supersecondary structure; hierarchic
Submitter: Connie Wang
Submission Date: April 24, 2018, 8:43 p.m.
|Number of data points||3|
|Proteins||Insulin ; Insulin|
|Assays/Quantities/Protocols||Experimental Assay: Cm ; Experimental Assay: m ; Experimental Assay: dG_H2O|
|Libraries||Mutations for sequence A:GIVEQCCTSICSLYQLENYCN/B:FVNQHLCGSHLVEALYLVCGERGFFYTPKT/C:GIVEQCCTSICSLYQLENYCN/D:FVNQHLCGSHLVEALYLVCGERGFFYTPKT/E:GIVEQCCTSICSLYQLENYCN/F:FVNQHLCGSHLVEALYLVCGERGFFYTPKT/G:GIVEQCCTSICSLYQLENYCN/H:FVNQHLCGSHLVEALYLVCGERGFFYTPKT/I:GIVEQCCTSICSLYQLENYCN/J:FVNQHLCGSHLVEALYLVCGERGFFYTPKT/K:GIVEQCCTSICSLYQLENYCN/L:FVNQHLCGSHLVEALYLVCGERGFFYTPKT|