Molecular basis for differential PIP-mediated association between vinculin and its splice isoform metavinculin.

Vinculin (Vcn) and its splice variant metavinculin (MVcn) are cell adhesion proteins that regulate cell morphology, adhesion, and motility. They function as scaffold proteins that anchor membrane receptors to filamentous actin (F-actin) at focal adhesions and cell-cell junctions. MVcn bears an extra 68 amino acid insert in the tail domain and is selectively expressed in cardiac and smooth muscle cells at substoichiometric levels relative to Vcn. Mutations in the MVcn tail domain (MVt) promote cardiomyopathy, yet how these mutations alter ligand interactions to promote defects in force transduction and reduced blood flow is unclear. One difference between Vcn and MVcn lies in the ability to reorganize F-actin, with MVcn negatively regulating Vcn-mediated F-actin bundling. Vcn associates with phosphatidylinositol 4,5-bisphosphate (PIP) through its tail domain (Vt) to drive recruitment, activation, and focal adhesion turnover. However, it remains unclear whether MVcn specifically associates with PIP-containing membranes and how such interactions might influence its functional interplay with Vcn in tissues where both isoforms coexist. To evaluate the interaction of MVt and MVt cardiomyopathy mutants with PIP membranes in comparison with Vt, we conducted mutagenesis, phospholipid-association assays, and computational modeling. We found that MVt shows reduced association for PIP-containing liposomes relative to Vt due to sequence differences within the insert region. Moreover, mutations in MVt that promote cardiomyopathies do not affect PIP-dependent lipid association. These findings suggest that MVcn differs from Vcn in driving PIP-mediated membrane association and sheds light on the coordinate role of Vcn and MVcn in membrane association as well as MVcn cardiomyopathy defects.