# Molecular basis for differential PIP2-mediated association between vinculin and its splice isoform metavinculin

## TL;DR

This study explores how differences in the structure of vinculin and its variant metavinculin affect their interactions with cell membranes, which could explain heart disease caused by mutations.

## Contribution

The study reveals that metavinculin has reduced membrane association with PIP2 compared to vinculin, providing insight into cardiomyopathy mechanisms.

## Key findings

- Metavinculin's tail domain shows reduced PIP2 membrane association compared to vinculin's tail domain.
- Cardiomyopathy-promoting mutations in metavinculin do not affect PIP2-dependent lipid association.
- Differences in PIP2-mediated membrane association may explain functional distinctions between vinculin and metavinculin.

## Abstract

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 (PIP2) through its tail domain (Vt) to drive recruitment, activation, and focal adhesion turnover. However, it remains unclear whether MVcn specifically associates with PIP2-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 PIP2 membranes in comparison with Vt, we conducted mutagenesis, phospholipid-association assays, and computational modeling. We found that MVt shows reduced association for PIP2-containing liposomes relative to Vt due to sequence differences within the insert region. Moreover, mutations in MVt that promote cardiomyopathies do not affect PIP2-dependent lipid association. These findings suggest that MVcn differs from Vcn in driving PIP2-mediated membrane association and sheds light on the coordinate role of Vcn and MVcn in membrane association as well as MVcn cardiomyopathy defects.