2K9R

Enhancing the activity of insulin by stereospecific unfolding

Summary for 2K9R

• Entry DOI: 10.2210/pdb2k9r/pdb
• Related: 2K91
• Descriptor: Insulin (2 entities in total)
• Functional Keywords: hormone, insulin, mutant, carbohydrate metabolism, cleavage on pair of basic residues, diabetes mellitus, disease mutation, glucose metabolism, pharmaceutical, secreted
• Biological source: Homo sapiens (human); More
• Cellular location: Secreted: P01308 P01308
• Total number of polymer chains: 2
• Total formula weight: 5718.50

Authors

Hua, Q.X.,Xu, B.,Huang, K.,Hu, S.Q.,Nakarawa, S.,Jia, W.H.,Philips, N.F.P.,Wittaker, L.,Wittaker, J.,Katsoyannis, P.G.,Weiss, M.A. (deposition date: 2008-10-23, release date: 2008-11-11, Last modification date: 2021-10-20)

Primary citation

Hua, Q.X.,Xu, B.,Huang, K.,Hu, S.Q.,Nakagawa, S.,Jia, W.,Wang, S.,Whittaker, J.,Katsoyannis, P.G.,Weiss, M.A.
Enhancing the Activity of a Protein by Stereospecific Unfolding: CONFORMATIONAL LIFE CYCLE OF INSULIN AND ITS EVOLUTIONARY ORIGINS.
J.Biol.Chem., 284:14586-14596, 2009

PubMed Abstract: A central tenet of molecular biology holds that the function of a protein is mediated by its structure. An inactive ground-state conformation may nonetheless be enjoined by the interplay of competing biological constraints. A model is provided by insulin, well characterized at atomic resolution by x-ray crystallography. Here, we demonstrate that the activity of the hormone is enhanced by stereospecific unfolding of a conserved structural element. A bifunctional beta-strand mediates both self-assembly (within beta-cell storage vesicles) and receptor binding (in the bloodstream). This strand is anchored by an invariant side chain (Phe(B24)); its substitution by Ala leads to an unstable but native-like analog of low activity. Substitution by d-Ala is equally destabilizing, and yet the protein diastereomer exhibits enhanced activity with segmental unfolding of the beta-strand. Corresponding photoactivable derivatives (containing l- or d-para-azido-Phe) cross-link to the insulin receptor with higher d-specific efficiency. Aberrant exposure of hydrophobic surfaces in the analogs is associated with accelerated fibrillation, a form of aggregation-coupled misfolding associated with cellular toxicity. Conservation of Phe(B24), enforced by its dual role in native self-assembly and induced fit, thus highlights the implicit role of misfolding as an evolutionary constraint. Whereas classical crystal structures of insulin depict its storage form, signaling requires engagement of a detachable arm at an extended receptor interface. Because this active conformation resembles an amyloidogenic intermediate, we envisage that induced fit and self-assembly represent complementary molecular adaptations to potential proteotoxicity. The cryptic threat of misfolding poses a universal constraint in the evolution of polypeptide sequences.

PubMed: 19321436
DOI: 10.1074/jbc.M900085200

Experimental method

SOLUTION NMR