Coupled motions direct electrons along human microsomal P450 Chains

Area of Science:

• Biochemistry
• Enzymology
• Protein Dynamics

Background:

• Protein domain motion is often linked to biological electron transfer, but its precise role remains unclear.
• Electron transfer from human NADPH-cytochrome P450 reductase (CPR) to cytochrome P450s (CYPs) involves motion, suggesting a functional significance.
• Understanding the interplay between enzyme dynamics and catalysis is key to deciphering complex biological redox processes.

Purpose of the Study:

• To investigate the hypothesis that enzyme motion, coupled with catalysis, creates "ready and waiting" states for electron transfer.
• To elucidate the dynamic conformational changes in CPR during its catalytic cycle.
• To establish the relationship between redox chemistry, ligand binding, and CPR's conformational states.

Main Methods:

• Developed a novel approach combining Förster Resonance Energy Transfer (FRET) with stopped-flow studies.
• Incorporated donor-acceptor fluorophores on the CPR surface to monitor conformational changes.
• Correlated observed conformational states (open/closed) with specific steps in the catalytic cycle.

Main Results:

• Demonstrated that reduction of flavin moieties in CPR induces an "opening" of the enzyme.
• Showed that ligand binding to CPR promotes a "closing" of the enzyme.
• Established a dynamic reaction cycle where closed states optimize internal electron transfer and open states signal readiness to partner CYPs.

Conclusions:

• CPR utilizes a dynamic cycle of opening and closing, tightly coupled to its redox chemistry, to facilitate vectorial electron transfer.
• This motion-driven mechanism optimizes electron transfer from NADPH to downstream heme, supporting all microsomal P450-catalyzed reactions.
• Enzyme motion is not stochastic but rather tightly regulated by chemistry, essential for efficient electron transfer in complex biological systems.