PMID: 23106217

Authors:

Dong X, Mi LZ, Zhu J, Wang W, Hu P, Luo BH, Springer TA

Title:

alpha(V)beta(3) Integrin Crystal Structures and Their Functional Implications.

Journal:

Biochemistry. 2012 Nov 6;51(44):8814-28. doi: 10.1021/bi300734n. Epub 2012 Oct, 29.

Abstract:

Many questions about the significance of structural features of integrin alpha(V)beta(3) with respect to its mechanism of activation remain. We have determined and re-refined crystal structures of the alpha(V)beta(3) ectodomain linked to C-terminal coiled coils (alpha(V)beta(3)-AB) and four transmembrane (TM) residues in each subunit (alpha(V)beta(3)-1TM), respectively. The alpha(V) and beta(3) subunits with four and eight extracellular domains, respectively, are bent at knees between the integrin headpiece and lower legs, and the headpiece has the closed, low-affinity conformation. The structures differ in the occupancy of three metal-binding sites in the betaI domain. Occupancy appears to be related to the pH of crystallization, rather than to the physiologic regulation of ligand binding at the central, metal ion-dependent adhesion site. No electron density was observed for TM residues and much of the alpha(V) linker. alpha(V)beta(3)-AB and alpha(V)beta(3)-1TM demonstrate flexibility in the linker between their extracellular and TM domains, rather than the previously proposed rigid linkage. A previously postulated interface between the alpha(V) and beta(3) subunits at their knees was also not supported, because it lacks high-quality density, required rebuilding in alpha(V)beta(3)-1TM, and differed markedly between alpha(V)beta(3)-1TM and alpha(V)beta(3)-AB. Together with the variation in domain-domain orientation within their bent ectodomains between alpha(V)beta(3)-AB and alpha(V)beta(3)-1TM, these findings are compatible with the requirement for large structural changes, such as extension at the knees and headpiece opening, in conveying activation signals between the extracellular ligand-binding site and the cytoplasm.