Actin activates a cryptic dimerization potential of the vinculin tail domain.
The tail domain of vinculin (V(t)) is an actin binding module containing two regions that interact with F-actin. Although intact V(t) purified from a bacterial expression system is a globular monomer, each actin binding region dimerizes when expressed individually, suggesting the presence of cryptic self-association sites whose exposure is regulated. We show that actin modulates V(t) self-association by inducing or stabilizing a conformational change in V(t) that allows dimerization. Chemical cross-linking studies implicate one of the actin binding regions in mediating dimerization in the presence of actin. Actin-induced V(t) dimers may play a role in the filament cross-linking activity of this protein. The V(t) dimers induced by actin are biochemically distinct from the V(t) dimers and higher oligomers induced by acidic phospholipids such as phosphatidylinositol 4,5-bisphosphate, suggesting structural differences in V(t) bound to these two ligands that may provide a mechanistic basis for inhibition of F-actin binding by phosphatidylinositol 4,5-bisphosphate. The ability of actin to regulate the dimerization state of an actin binding protein suggests that, rather than serving a passive structural role, actin filaments may directly participate in signal transduction and other cellular events that are known to depend on cytoskeletal integrity.
Johnson
R P
RP
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Craig
S W
SW
D000199:Actins / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002645:Chickens; D003432:Cross-Linking Reagents; D019281:Dimerization; D008024:Ligands; D008840:Microfilament Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D008956:Models, Chemical; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D010743:Phospholipids / Q000494:pharmacology; D018583:Pliability; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016596:Vinculin / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
D000199:Actins; D003432:Cross-Linking Reagents; D008024:Ligands; D008840:Microfilament Proteins; D010446:Peptide Fragments; D010743:Phospholipids; D011993:Recombinant Fusion Proteins; D016596:Vinculin