Select Configurational Dynamics in Ethanolamine Ammonia-Lyase Radical Enzyme Catalysis

Area of Science:

• Biochemistry
• Enzyme kinetics
• Protein dynamics

Background:

• Enzyme catalysis is complex, involving protein and solvent contributions.
• Adenosylcobalamin (coenzyme B12)-dependent ethanolamine ammonia-lyase (EAL) is crucial for amino acid metabolism.
• Understanding the interplay between protein structure, solvent dynamics, and reaction mechanisms is vital.

Purpose of the Study:

• To investigate the role of protein and coupled solvent configurational fluctuations in EAL enzyme catalysis.
• To elucidate the molecular mechanism of substrate radical reactions in EAL under varying solvent conditions.
• To establish a mechanistic link between solvent dynamics and enzyme turnover.

Main Methods:

• Time-resolved electron paramagnetic resonance (EPR) spectroscopy was employed to study EAL kinetics.
• Temperature dependence of substrate radical reactions was measured in frozen solutions with varying hydration and cosolvent layers.
• EPR spin probe mobility and electric permittivity were used to probe solvent dynamics.

Main Results:

• A kinetic bifurcation was observed in the Arrhenius relation, transitioning from monoexponential to biexponential dependence with decreasing temperature.
• Solvent dynamics showed a transition from collective cluster to individual fluctuations, coinciding precisely with the kinetic bifurcation.
• Arrhenius dependences collapsed onto a universal pattern when shifted, indicating coupled protein-hydration layer dynamics.

Conclusions:

• Specific collective fluctuations in the EAL hydration layer are coupled to active-site configurational fluctuations.
• These coupled dynamics create low-barrier pathways, facilitating enzyme catalysis.
• The findings support a model where select collective configurational dynamics are fundamental to enzyme catalysis.