Specificity for Homooligomer versus Heterooligomer Formation in Integrin Transmembrane Helices

JOURNAL OF MOLECULAR BIOLOGY

卷:401

Article

Zhu, Hua¹  Metcalf, Douglas G.²  Streu, Craig N.²  Billings, Paul C.²  DeGrado, William F.²  Bennett, Joel S.¹ 

[1] Univ Penn, Sch Med, Dept Med, Div Hematol Oncol, Philadelphia, PA 19104 USA

[2] Univ Penn, Sch Med, Dept Biochem & Biophys, Philadelphia, PA 19104 USA

关键词: integrin;    transmembrane domains;    oligomerization motifs;    TOXCAT;    scanning mutagenesis;   

DOI  :  10.1016/j.jmb.2010.06.062

来源: Elsevier

【 摘 要 】

Transmembrane (TM) helices engage in homomeric and heteromeric interactions that play essential roles in the folding and assembly of TM proteins. However, features that explain their propensity to interact homomerically or heteromerically and determine the strength of these interactions are poorly understood. Integrins provide an ideal model system for addressing these questions because the TM helices of full-length integrins interact heteromerically when integrins are inactive, but isolated TM helices are also able to form homodimers or homooligomers in micelles and bacterial membranes. We sought to determine the features defining specificity for homointeractions versus heterointeractions by conducting a comprehensive comparison of the homomeric and heteromeric interactions of integrin alpha IIb beta 3 TM helices in biological membranes. Using the TOXCAT assay, we found that residues V700, M701, A703, I704, L705, G708, L709, L712, and L713, which are located on the same face of the beta 3 helix, mediate homodimer formation. We then characterized the beta 3 heterodimer by measuring the ability of beta 3 helix mutations to cause ligand binding to alpha IIb beta 3. We found that mutating V696, L697, V700, M701, A703. 1704, L705, G708, L712, and L713, but not the small residue-X-3-small residue motif S699-X-3-A703, caused constitutive alpha IIb beta 3 activation, as well as persistent focal adhesion kinase phosphorylation dependent on alpha IIb beta 3 activation. Because alpha IIb and beta 3 use the same face of their respective TM helices for homomeric and heteromeric interactions, the interacting surface on each has an intrinsic stickiness predisposing towards helix-helix interactions in membranes. The residues responsible for heterodimer formation comprise a network of interdigitated side chains with considerable geometric complementarity; mutations along this interface invariably destabilize heterodimer formation. By contrast, residues responsible for homomeric interactions are dispersed over a wider surface. While most mutations of these residues are destabilizing, some stabilized homooligomer formation. We conclude that the alpha IIb beta 3 TM heterodimer shows the hallmark of finely tuned heterodimeric interaction, while homomeric interaction is less specific. (C) 2010 Elsevier Ltd. All rights reserved.

【 授权许可】

Free