title: Determination of the enhancing action of HSP90 on neuronal nitric oxide synthase by EPR spectroscopy.
abstract: Recent studies showed that heat shock protein 90 (HSP90) enhances nitric oxide (NO) synthesis from endothelial and neuronal NO synthase (eNOS and nNOS, respectively). However, these findings were based on indirect NO measurements. Moreover, although our previous studies showed that the action of HSP90 involves increased Ca(2+)/calmodulin (Ca(2+)/CaM) binding, quantitative measurements of the effect of HSP90 on CaM binding to nNOS have been lacking. With electron paramagnetic resonance spectroscopy, we directly measured NO signals from purified nNOS. HSP90 augmented NO formation from nNOS in a dose-dependent manner. Tryptophan fluorescence-quenching measurements revealed that HSP90 markedly reduced the K(d) of CaM to nNOS (0.5 +/- 0.1 nM vs. 9.4 +/- 1.8 nM in the presence and absence of HSP90, P < 0.01). Ca(2+) ionophore triggered strong NO production from nNOS-transfected cells, and this was significantly reduced by the HSP90 inhibitor geldanamycin. Thus these studies provide direct evidence demonstrating that HSP90 enhances nNOS catalytic function in vitro and in intact cells. The effect of HSP90 is mediated by the enhancement of CaM binding to nNOS.
authors.affiliation: Department of Medicine, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21224, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Song
authors.forename: J L
authors.initials: JL
authors.lastname: Zweier
authors.forename: Y
authors.initials: Y
authors.lastname: Xia
mesh_terms: D016227:Benzoquinones; D002147:Calmodulin / Q000378:metabolism*; D002460:Cell Line; D004578:Electron Spin Resonance Spectroscopy; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D047029:Lactams, Macrocyclic; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D011809:Quinones / Q000494:pharmacology
chemical_list: D016227:Benzoquinones; D002147:Calmodulin; D004791:Enzyme Inhibitors; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D011809:Quinones; D009569:Nitric Oxide; C496320:NOS1 protein, human; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D019331:NG-Nitroarginine Methyl Ester; C001277:geldanamycin