Direct Interaction of Endothelial Nitric-oxide Synthase and Caveolin-1 Inhibits Synthase Activity

Endothelial nitric-oxide synthase (eNOS) and caveolin-1 are associated within endothelial plasmalemmal caveolae. It is not known, however, whether eNOS and caveolin-1 interact directly or indirectly or whether the interaction affects eNOS activity. To answer these questions, we have cloned the bovine caveolin-1 cDNA and have investigated the eNOS-caveolin-1 interaction in an in vitro binding assay system using glutathione S-transferase (GST)-caveolin-1 fusion proteins and baculovirus-expressed bovine eNOS. We have also mapped the domains involved in the interaction using an in vivo yeast two-hybrid system. Results obtained using both in vitro and in vivo protein interaction assays show that both N- and C-terminal cytosolic domains of caveolin-1 interact directly with the eNOS oxygenase domain. Interaction of eNOS with GST-caveolin-1 fusion proteins significantly inhibits enzyme catalytic activity. A synthetic peptide corresponding to caveolin-1 residues 82-101 also potently and reversibly inhibits eNOS activity by interfering with the interaction of the enzyme with Ca2+/calmodulin (CaM). Regulation of eNOS in endothelial cells, therefore, may involve not only positive allosteric regulation by Ca2+/CaM, but also negative allosteric regulation by caveolin-1.