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Updated: May 21, 2026

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes
Published on: January 16, 2016
An outer membrane protein undergoes enthalpy- and entropy-driven transitions.
Belete R Cheneke1, Mridhu Indic, Bert van den Berg
1Department of Physics, Syracuse University, 201 Physics Building, Syracuse, NY 13244-1130, USA.
Outer membrane carboxylate channels like OccK1 exhibit complex gating dynamics with both enthalpy-driven and entropy-driven transitions. Temperature influences the most favorable open state, revealing distinct functional traits of beta-barrel proteins.
Area of Science:
- Biophysics
- Structural Biology
- Membrane Protein Dynamics
Background:
- Beta-barrel membrane proteins are crucial for cellular transport but their gating mechanisms remain incompletely understood.
- Outer membrane carboxylate channels (OccK1) are essential for nutrient uptake in bacteria.
Purpose of the Study:
- To investigate the discrete gating dynamics of the outer membrane carboxylate channel OccK1.
- To elucidate the role of enthalpy and entropy in OccK1 channel transitions.
- To determine the effect of temperature on OccK1 substate populations.
Main Methods:
- Single-molecule electrophysiology analysis at varying temperatures.
- Rational protein design of OccK1 variants (native and loop-deletion).
- Analysis of channel transition enthalpies, entropies, and free energies.
Main Results:
- OccK1 displays discrete gating dynamics with both enthalpy-driven and entropy-driven current transitions.
- Protein design revealed significant changes in activation enthalpies and entropies, but not equilibrium free energies.
- Observed counterintuitive negative activation enthalpy compensated by decreased activation entropy.
- Temperature scanning showed a thermally induced switch in the most favorable open substate at 4 °C.
Conclusions:
- OccK1 gating is complex, involving distinct enthalpy and entropy contributions.
- The channel remains at equilibrium throughout its transitions.
- Temperature significantly impacts the conformational preferences and functional states of OccK1, highlighting its adaptability.
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