Oligomerization of VIP21‐caveolin in vitro is stabilized by long chain fatty acylation or cholesterol

Abstract

VIP21‐caveolin is one of the components which form the cytoplasmic surface of caveolae. In vivo, this integral membrane protein is found in homo‐oligomers with molecular masses of approximately 200, 400 and 600 kDa. These oligomers are also formed by the addition of cytosol to the in vitro synthesized and membrane inserted VIP21‐caveolin. Here we show that long chain fatty acyl coenzyme A esters can completely substitute for cytosol in inducing 200 kDa and 400 kDa complexes, whereas 25‐hydroxy‐cholesterol can produce the 200 kDa oligomer. In order to understand whether acylation of VIP21‐caveolin itself is a prerequisite for oligomerization, we studied a mutant protein lacking all three cysteines. When analyzed by velocity sucrose gradient centrifugation in the presence of the non‐ionic detergent octylglucoside, both palmitoylated and non‐palmitoylated VIP21‐caveolin formed oligomers that were indistinguishable. However, only the oligomers of the non‐palmitoylated protein are disrupted when analyzed by SDS‐PAGE without boiling. These data suggest that the protein domains of VIP21‐caveolin are the primary determinants of oligomerization, but that palmitoylation of cysteine residues can increase the stability of the oligomers.