Meta-vinculin - A vinculin-related protein with solubility properties of a membrane protein

The localization of vinculin, an actin-binding protein^1,2 of molecular weight 130,000 (130K) at a variety of cytoskeletal-associated membrane specializations including the zonula adherens of intestinal epithelial cells³, fascia adherens of intercalated discs³, focal adhesion plaques in fibroblasts^4,5, and costameres (sarcolemmal domains in periodic register with the I-bands of subjacent myofibrils) in cardiac and skeletal muscle⁶, suggests that vinculin could link actin to cell membranes. This hypothesis is supported by immuno-ultrastructural studies which show that vinculin is closely apposed to the plasma membrane at sites where actin-containing microfilaments terminate^3,7. But since vinculin has the solubility properties of a peripheral membrane protein ⁴, there would also need to be an integral membrane component to which it bound to link actin filaments to the plasma membrane. Our efforts to identify the presumed membrane binding site for vinculin resulted instead in the detection of a 150K protein which we term meta-vinculin (Greek meta among, with; in the sense of closely related to), that is immunologically related to 130K vinculin. Unlike vinculin, meta-vinculin has the solubility properties of an integral membrane protein. Given its location within the cell, it is possible that meta-vinculin is an integral membrane anchor protein for actin filaments.