Neuronal nitric-oxide synthase (nNOS) has been shown previously to interact with α1-syntrophin in the dystrophin complex of skeletal muscle. In the present study, we have examined whether nNOS also interacts with caveolin-3 in skeletal muscle. nNOS and caveolin-3 are coimmunoprecipitated from rat skeletal muscle homogenates by antibodies directed against either of the two proteins. Synthetic peptides corresponding to the membrane-proximal caveolin-3 residues 65-84 and 109-130 and homologous caveolin-1 residues 82- 101 and 135-156 potently inhibit the catalytic activity of purified, recombinant nNOS. Purified nNOS also binds to a glutathione S-transferase- caveolin-1 fusion protein in in vitro binding assays. In vitro binding is completely abolished by preincubation of nNOS with either of the two caveolin-3 inhibitory peptides. Interactions between nNOS and caveolin-3, therefore, appear to be direct and to involve two distinct caveolin scaffolding/inhibitory domains. Other caveolin-interacting enzymes, including endothelial nitric-oxide synthase and the c-Src tyrosine kinase, are also potently inhibited by each of the four caveolin peptides. Inhibitory interactions mediated by two different caveolin domains may thus be a general feature of enzyme docking to caveolin proteins in plasmalemmal caveolae.
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