Diabetes-Associated Mutations in Insulin Identify Invariant Receptor Contacts

Mutations in human insulin cause an autosomal-dominant syndrome of diabetes and fasting hyperinsulinemia. We demonstrate by residue-specific photo cross-linking that diabetes-associated mutations occur at receptor-binding sites. The studies use para -azido-phenylalanine, introduced at five sites by total protein synthesis. Because two such sites (Val A3 and Phe B24 ) are largely buried in crystal structures of the free hormone, their participation in receptor binding is likely to require a conformational change to expose a hidden functional surface. Our results demonstrate that this surface spans both chains of the insulin molecule and includes sites of rare human mutations that cause diabetes.