Fluorescence quenching studies of structure and dynamics in calmodulin-eNOS complexes

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Endothelial nitric oxide synthase (eNOS) plays a crucial role in vascular homeostasis.
• Activation of eNOS by calmodulin (CaM) is essential for its function but the underlying conformational changes are not fully understood.
• Understanding these dynamics is key to elucidating eNOS regulation and signaling.

Purpose of the Study:

• To investigate the conformational states of eNOS upon calmodulin binding.
• To characterize the dynamics and transitions between these states at the single-molecule level.
• To propose a model linking fluorescence quenching to specific enzyme conformations.

Main Methods:

• Utilizing fluorescence decays of fluorescently labeled CaM bound to eNOS.
• Analyzing single-molecule fluorescence trajectories to observe state transitions.
• Developing a model to correlate fluorescence quenching states with enzyme conformations.

Main Results:

• Identified four distinct conformational states of CaM bound to eNOS.
• Observed transitions between these states on millisecond to second time scales.
• Proposed that the most quenched state corresponds to CaM docked to the eNOS oxygenase domain.
• Single-molecule data showed time lags consistent with oxygenase activity in the docked state.

Conclusions:

• Calmodulin binding induces a dynamic sequence of conformational states in eNOS.
• The proposed model provides a framework for understanding CaM-eNOS interactions and their functional implications.
• These findings offer insights into the regulation of nitric oxide production by eNOS.