Holoenzyme structures of endothelial nitric oxide synthase - An allosteric role for calmodulin in pivoting the FMN domain for electron transfer

Niels Volkmann, Pavel Martásek, Linda J. Roman, Xiao Ping Xu, Christopher Page, Mark Swift, Dorit Hanein, Bettie Sue Masters

Research output: Contribution to journalArticle

24 Scopus citations


While the three-dimensional structures of heme- and flavin-binding domains of the NOS isoforms have been determined, the structures of the holoenzymes remained elusive. Application of electron cryo-microscopy and structural modeling of the bovine endothelial nitric oxide synthase (eNOS) holoenzyme produced detailed models of the intact holoenzyme in the presence and absence of Ca2+/calmodulin (CaM). These models accommodate the cross-electron transfer from the reductase in one monomer to the heme in the opposite monomer. The heme domain acts as the anchoring dimeric structure for the entire enzyme molecule, while the FMN domain is activated by CaM to move flexibly to bridge the distance between the reductase and oxygenase domains. Our results indicate that the key regulatory role of CaM involves the stabilization of structural intermediates and precise positioning of the pivot for the FMN domain tethered shuttling motion to accommodate efficient and rapid electron transfer in the homodimer of eNOS.

Original languageEnglish (US)
Pages (from-to)46-54
Number of pages9
JournalJournal of Structural Biology
Issue number1
Publication statusPublished - Oct 1 2014



  • Calmodulin
  • Electron cryomicroscopy
  • Electron transfer
  • Image processing
  • Nitric oxide synthase
  • Three-dimensional reconstruction

ASJC Scopus subject areas

  • Structural Biology

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