Year: 2025
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide Contributions of protein and coupled solvent configurational fluctuations to the molecular mechanism of enzyme catalysis are addressed in the adenosylcobalamin (coenzyme B 12 )-dependent ethanolamine ammonia-lyase (EAL) enzyme from Salmonella enterica serovar Typhimurium. Full-spectrum, time-resolved electron paramagnetic resonance (EPR) spectroscopy is used to measure the temperature dependence of the first-order kinetics of the substrate radical reaction in EAL surrounded by successive hydration and aqueous-cosolvent (aminoethanol; added dimethyl sulfoxide, glycerol, and sucrose) layers in frozen solution. At different temperature ( T ) values in each system, the piecewise-continuous Arrhenius relation displays the characteristic bifurcation, from high- T monoexponential dependence (reaction from substrate radical macrostate, S • ) to the low- T biexponential dependence (reaction from sequential substates, S 1 • and S 2 • ). Parallel measurements of the solvent dynamics around EAL by using EPR spin probe mobility or electric permittivity detect a dynamical transition from collective cluster to individual fluctuations of coupled protein surface groups and hydration water, with decreasing T, that precisely coincides with the kinetic bifurcation T in each solvent system. When shifted along their common monotonic high- T relation, the Arrhenius dependences collapse onto a single, universal pattern. The results indicate that specific, or select, collective fluctuations in the EAL protein hydration layer are coupled to active-site configurational fluctuations, providing low-barrier portals through the configuration space. The direct mechanistic link between solvent dynamics and turnover expands the understanding of radical-mediated reactions in EAL and supports the model that select collective configurational dynamics are a fundamental feature of enzyme catalysis.
Source: ACS Physical Chemistry Au
Authors: Wei Li, Andrew M. Stewart, Kurt Warncke
Institution: Emory University
Language: English
Subfield: Biophysics
Domain: Life Sciences
Open Access status: gold
Estimated APC paid: $3,500
OpenAlex ID: W4413906459