Maintenance of the B-chain beta-turn in [GlyB24] insulin mutants: a steady-state fluorescence anisotropy study.

[GlyB24]insulin is a novel insulin analog which maintains nearly full biological activity [Mirmira, R. G., & Tager, H. S. (1989) J. Biol. Chem. 264, 6349−6354] even though its structure, as determined by 2D NMR, shows complete loss of the characteristic B-chain β-turn [Hua, Q. X., Shoelson, S. E., Kochoyan, M., & Weiss, M. A. (1991) Nature 354, 238−241], which in native insulin allows the extended B-chain C-terminal region to fold against the central B-chain helix. In these studies, steady-state anisotropy measurements and fluorescence quenching analysis of the tryptophan-substituted analogs [TrpB25]insulin and [GlyB24,TrpB25]insulin have been used to study the structure of the C-terminal region of the B-chain and have demonstrated that [GlyB24]insulin mutants maintain the normal B-chain conformation to a degree comparable to that of native (PheB24) insulin at neutral pH. The tryptophan-substituted, B-chain C-terminally truncated analogs [TrpB25-α-carboxamide]despentapeptide(B26−B30)-insulin (DPI) and [Gl...