Cysteine post‐translational modifications regulate protein interactions of caveolin‐3

Abstract

Caveolae are small flask‐shaped invaginations of the surface membrane which are proposed to recruit and co‐localize signaling molecules. The distinctive caveolar shape is achieved by the oligomeric structural protein caveolin, of which three isoforms exist. Aside from the finding that caveolin‐3 is specifically expressed in muscle, functional differences between the caveolin isoforms have not been rigorously investigated. Caveolin‐3 is relatively cysteine‐rich compared to caveolins 1 and 2, so we investigated its cysteine post‐translational modifications. We find that caveolin‐3 is palmitoylated at 6 cysteines and becomes glutathiolated following redox stress. We map the caveolin‐3 palmitoylation sites to a cluster of cysteines in its C terminal membrane domain, and the glutathiolation site to an N terminal cysteine close to the region of caveolin‐3 proposed to engage in protein interactions. Glutathiolation abolishes caveolin‐3 interaction with heterotrimeric G protein alpha subunits. Our results indicate that a caveolin‐3 oligomer contains up to 66 palmitates, compared to up to 33 for caveolin‐1. The additional palmitoylation sites in caveolin‐3 therefore provide a mechanistic basis by which caveolae in smooth and striated muscle can possess unique phospholipid and protein cargoes. These unique adaptations of the muscle‐specific caveolin isoform have important implications for caveolar assembly and signaling.