Primary Citation of Related Structures:   1XW7
PubMed Abstract: 
Naturally occurring mutations in insulin associated with diabetes mellitus identify critical determinants of its biological activity. Here, we describe the crystal structure of insulin Wakayama, a clinical variant in which a conserved valine in the A ...
Naturally occurring mutations in insulin associated with diabetes mellitus identify critical determinants of its biological activity. Here, we describe the crystal structure of insulin Wakayama, a clinical variant in which a conserved valine in the A chain (residue A3) is substituted by leucine. The substitution occurs within a crevice adjoining the classical receptor-binding surface and impairs receptor binding by 500-fold, an unusually severe decrement among mutant insulins. To resolve whether such decreased activity is directly or indirectly mediated by the variant side chain, we have determined the crystal structure of Leu(A3)-insulin and investigated the photo-cross-linking properties of an A3 analogue containing p-azidophenylalanine. The structure, characterized in a novel crystal form as an R(6) zinc hexamer at 2.3 A resolution, is essentially identical to that of the wild-type R(6) hexamer. The variant side chain remains buried in a nativelike crevice with small adjustments in surrounding side chains. The corresponding photoactivatable analogue, although of low affinity, exhibits efficient cross-linking to the insulin receptor. The site of photo-cross-linking lies within a 14 kDa C-terminal domain of the alpha-subunit. This domain, unrelated in sequence to the major insulin-binding region in the N-terminal L1 beta-helix, is also contacted by photoactivatable probes at positions A8 and B25. Packing of Val(A3) at this interface may require a conformational change in the B chain to expose the A3-related crevice. The structure of insulin Wakayama thus evokes the reasoning of Sherlock Holmes in "the curious incident of the dog in the night": the apparent absence of structural perturbations (like the dog that did not bark) provides a critical clue to the function of a hidden receptor-binding surface.
Related Citations: 
Crystallographic titration of cubic insulin crystals: pH affects GluB13 switching and sulfate binding Diao, J. (2003) Acta Crystallogr D Biol Crystallogr 59: 670
Structure of cubic insulin crystals in glucose solutions Yu, B., Caspar, D.L. (1998) Biophys J 74: 616
Structure of the pig insulin dimer in the cubic crystal Badger, J., Harris, M.R., Reynolds, C.D., Evans, A.C., Dodson, E.J., Dodson, G.G., North, A.C. (1991) Acta Crystallogr B 47: 127
Water structure in cubic insulin crystals Badager, J., Caspar, D.L. (1991) Proc Natl Acad Sci U S A 88: 622
Zinc-free cubic pig insulin: crystallization and structure determination Dodson, E.J., Dodson, G.G., Lewitova, A., Sabesan, M. (1978) J Mol Biol 125: 387
Organizational Affiliation: 
Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4935, USA.