Differential lipid binding of vinculin isoforms promotes quasi-equivalent dimerization

Area of Science:

• Cardiovascular Biology
• Molecular Cell Biology
• Biochemistry

Background:

• Dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM) are leading causes of heart failure, often linked to mutations in adhesion complex proteins.
• Vinculin is crucial for cardiac function, particularly at intercalated discs, and mutations in vinculin lead to debilitating heart conditions.
• The muscle-specific isoform, metavinculin (MV), contains a unique insert where DCM/HCM-associated mutations are found.

Purpose of the Study:

• To investigate the role of phosphoinositol-4,5-bisphosphate (PIP2) in regulating metavinculin (MV) dimerization and function.
• To elucidate the structural differences between vinculin and MV dimerization in response to phospholipid binding.
• To understand how DCM/HCM-associated mutations in MV affect its interaction with PIP2 and its dimeric state.

Main Methods:

• Biochemical assays to study PIP2 binding and MV dimerization.
• Structural analysis to compare vinculin and MV dimer interfaces.
• Site-directed mutagenesis to probe the function of specific residues and isoform-specific differences.

Main Results:

• Phospholipid binding induces a domain-swapped symmetric MV dimer, distinct from the asymmetric vinculin dimer.
• The symmetric MV dimer binds two PIP2 molecules, while the vinculin dimer binds only one.
• Wild-type MV and the R975W mutant bind PIP2 in inactive conformations, with R975W MV showing impaired dimerization.
• Mutational analysis confirmed that residues dictate isoform-specific dimerization and lipid binding.

Conclusions:

• MV homodimerization, modulated by PIP2, plays a significant role in microfilament attachment at muscular adhesion sites.
• These findings advance the understanding of MV's function in cardiac remodeling and the mechanisms underlying DCM and HCM.
• The distinct PIP2-mediated dimerization of MV compared to vinculin highlights isoform-specific regulation in cardiac health and disease.