Calmodulin activates neuronal nitric oxide synthase by enabling transitions between conformational states

• Published in: FEBS letters Vol. 587; no. 1; pp. 44 - 47
• Main Authors: Salerno, John C., Ray, Krishanu, Poulos, Thomas, Li, Huiying, Ghosh, Dipak K.
• Format: Journal Article
• Language: English
• Published: England Elsevier B.V 04.01.2013
• Subjects: Algorithms; Binding Sites; Calmodulin; Calmodulin - chemistry; Calmodulin - metabolism; CaM; Enzyme Activation; FAD; Flavin adenine di-nucleotide; Flavin mono nucleotide; Flavin Mononucleotide - metabolism; Fluorescence; FMN; Hemin - metabolism; Holoenzymes - chemistry; Holoenzymes - genetics; Holoenzymes - metabolism; Humans; inducible NOS; iNOS; Kinetics; Mechanism; Mutant Proteins - chemistry; Mutant Proteins - metabolism; neuronal NOS; Nitric oxide synthase; Nitric Oxide Synthase Type I - chemistry; Nitric Oxide Synthase Type I - genetics; Nitric Oxide Synthase Type I - metabolism; nNOS; NOS; oxyFMN; PBS-T; phosphate buffer saline-Tween-20 (see Section 2); Protein Conformation; Protein Interaction Domains and Motifs; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Spectrometry, Fluorescence; two-domain NOS construct (FMN and oxygenase domains); NOS; FMN; nNOS; FAD; Fluorescence; iNOS; Nitric oxide synthase; oxyFMN; CaM; PBS-T; Calmodulin; Mechanism
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/j.febslet.2012.10.039

► nNOS reductase conformations are characterized by FMN fluorescence lifetimes. ► Calmodulin conformationally activates electron transfer and NO synthesis. ► CaM binding shifts nNOS from input conformations to “open” and output states. ► The DG810 mutant of nNOS is less conformationally constrained than wild type. We recently showed that inducible nitric oxide synthase conformational intermediates can be resolved via FMN fluorescence lifetimes. Here we show that neuronal NOS activation by calmodulin removes constraints favoring a closed ‘input state’, increasing occupation of other states and facilitating conformational transitions. The 90ps FMN input state lifetime distinguishes it from ∼4ns ‘open’ states in which FMN does not interact strongly with other groups, or 0.9ns output states in which FMN interacts with ferriheme. Enablement of the conformational cycle is an important paradigm for control in nNOS and related enzymes, and may extend to other control modalities.