Differential actin organization by vinculin isoforms: implications for cell type-specific microfilament anchorage.

Vinculin is found in all adherens junctions, while metavinculin, a larger splice variant, is coexpressed with vinculin only in smooth and cardiac muscle. To understand the significance of metavinculin expression, we compared ligand binding between turkey vinculin and metavinculin. Residues 1-258 were found essential for head-tail interactions in both proteins. The tail domains (VT and MVT, respectively) both bind to F-actin. However, while VT bundles F-actin, MVT generates highly viscous F-actin webs. In transfected PtK2 cells, VT causes F-actin needles or coils, while MVT-expressing cells display a diffuse F-actin distribution. Thus, the MVT-specific insert induces an F-actin supraorganization different from the VT-based form, suggesting that metavinculin has a specific role in muscle.