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Updated: May 16, 2026
07:51
Pull-down of Calmodulin-binding Proteins
Published on: January 23, 2012
Calmodulin activates neuronal nitric oxide synthase by enabling transitions between conformational states
John C Salerno1, Krishanu Ray, Thomas Poulos
1Department of Biology, Kennesaw State University, Kennesaw, GA 30144, United States. jsalern3@kennesaw.edu
FEBS Letters
|November 20, 2012
Summary
Neuronal nitric oxide synthase (nNOS) activation by calmodulin shifts its conformational states, revealed by FMN fluorescence lifetimes. This dynamic conformational cycle is key to nNOS enzyme control.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Inducible nitric oxide synthase (iNOS) conformational intermediates were previously resolved using FMN fluorescence lifetimes.
- Neuronal nitric oxide synthase (nNOS) plays a critical role in neurotransmission and requires precise regulatory mechanisms.
Purpose of the Study:
- To investigate the effect of calmodulin activation on nNOS conformational states.
- To elucidate the role of conformational dynamics in nNOS enzyme regulation.
Main Methods:
- Utilized FMN (flavin mononucleotide) fluorescence lifetime measurements to resolve nNOS conformational intermediates.
- Analyzed changes in FMN fluorescence lifetimes upon calmodulin binding to nNOS.
Main Results:
- Calmodulin activation of nNOS releases constraints on a closed 'input state', promoting transitions to other conformational states.
- Identified distinct FMN fluorescence lifetimes for different nNOS states: 90 ps for the input state, ~4 ns for open states, and 0.9 ns for output states.
- Demonstrated that calmodulin facilitates the nNOS conformational cycle.
Conclusions:
- Calmodulin binding induces significant conformational changes in nNOS, shifting the equilibrium between different functional states.
- The conformational cycle enabled by calmodulin is a critical regulatory mechanism for nNOS activity.
- This regulatory paradigm may be applicable to other related enzymes and control mechanisms.
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