1. Contribution of TyrB26 to the Function and Stability of Insulin.
- Author
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Pandyarajan, Vijay, Phillips, Nelson B., Rege, Nischay, Lawrence, Michael C., Whittaker, Jonathan, and Weiss, Michael A.
- Subjects
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CRYSTAL defects , *HORMONE receptors , *SUBSTITUENTS (Chemistry) , *ZINC ions ,INSULIN stability - Abstract
Crystallographic studies of insulin bound to receptor domains have defined the primary hormone-receptor interface. Weinvestigated the role of TyrB26, a conserved aromatic residue at this interface. To probe the evolutionary basis for such conservation, we constructed 18 variants at B26. Surprisingly, nonaromatic polar or charged side chains (such as Glu, Ser, or ornithine (Orn)) conferred high activity, whereas the weakestbinding analogs contained Val, Ile, and Leu substitutions. Modeling of variant complexes suggested that the B26 side chains pack within a shallow depression at the solvent-exposed periphery of the interface. This interface would disfavor large aliphatic side chains. The analogs with highest activity exhibited reduced thermodynamic stability and heightened susceptibility to fibrillation. Perturbed self-assembly was also demonstrated in studies of the charged variants (Orn and Glu); indeed, the GluB26 analog exhibited aberrant aggregation in either the presence or absence of zinc ions. Thus, although TyrB26 is part of insulin's receptor-binding surface, our results suggest that its conservation has been enjoined by the aromatic ring's contributions to native stabilityand self-assembly. We envisage that such classical structural relationships reflect the implicit threat of toxic misfolding (rather than hormonal function at the receptor level) as a general evolutionary determinant of extant protein sequences. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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