Direct extracellular contact between integrin alpha(3)beta(1) and TM4SF protein CD151

Previously we established that the alpha(3)beta(1) integrin shows stable, s pecific, and stoichiometric association with the TM4SF (tetraspannin) prote in CD151. Here we used a membrane impermeable cross-linking agent to show a direct association between extracellular domains of alpha(3)beta(1) and CD 151. The alpha(3)beta(1)-CD151 association site was then mapped using chime ric alpha(6)/alpha(3) integrins and CD151/NAG2 TM4SF proteins. Complex form ation required an extracellular alpha(3) Site (amino acids (aa) 570-705) no t previously known to be involved in specific integrin contacts with other proteins and a region (aa 186-217) within the large extracellular loop of C D151. Notably, the anti-CD151 monoclonal antibody TS151r binding epitope, p reviously implicated in alpha(3) integrin association, was mapped to the sa me region of CD151 (aa 186-217). Finally, we demonstrated that both NH2- an d COOH-terminal domains of CD151 are located on the inside of the plasma me mbrane, thus confirming a long suspected model of TM4SF protein topology.