1xw7: Difference between revisions

[[Image:1xw7.gif|left|200px]]<br /><applet load="1xw7" size="350" color="white" frame="true" align="right" spinBox="true"  

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.

1XW7 is a [http://en.wikipedia.org/wiki/Protein_complex Protein complex] structure of sequences from [http://en.wikipedia.org/wiki/ ] with <scene name='pdbligand=ZN:'>ZN</scene>, <scene name='pdbligand=CL:'>CL</scene> and <scene name='pdbligand=IPH:'>IPH</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1XW7 OCA].  

[[Category: Chu, Y C.]]

[[Category: Hu, S Q.]]

[[Category: Katsoyannis, P G.]]

[[Category: Wan, Z L.]]

[[Category: Weiss, M A.]]

''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 15:59:15 2008''