Single-molecule spectroscopy reveals how calmodulin activates NO synthase by controlling its conformational...

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Nitric oxide synthase (NOS) enzymes are crucial in biological and medical fields.
• Understanding the regulatory mechanisms of NOS, particularly the role of domain motions and calmodulin binding in catalysis, remains unclear.

Purpose of the Study:

• To elucidate the conformational states and dynamics of neuronal NOS reductase domain using single-molecule FRET.
• To investigate how calmodulin binding influences these dynamics to regulate NOS catalysis.

Main Methods:

• Utilized single-molecule fluorescence resonance energy transfer (FRET) spectroscopy.
• Employed FRET dye-labeled neuronal NOS reductase domain to analyze conformational states and dynamics.
• Measured distance distributions and fluctuation rates between NOS domains.

Main Results:

• Calmodulin binding alters the distance distribution between NOS domains.
• Calmodulin binding shortens the conformational state lifetimes.
• Calmodulin binding imposes conformational discipline by narrowing state and fluctuation rate distributions.

Conclusions:

• Single-molecule FRET revealed calmodulin's precise effects on NOS conformational dynamics.
• Calmodulin promotes NOS catalysis by shaping its physical and temporal conformational behaviors.
• These findings offer insights into the molecular regulation of NOS activity.