Solute flux through a fluctuating membrane channel.

Area of Science:

• Biophysics
• Molecular Biology
• Membrane Transport

Background:

• Biological membrane protein channels exhibit dynamic thermal fluctuations.
• Channel gating, a key fluctuation, regulates transport but doesn't encompass all dynamic effects.
• Side chain fluctuations can significantly alter channel transport properties.

Purpose of the Study:

• To investigate the impact of a fluctuating side chain on protein channel transport.
• To analyze how side chain dynamics affect solute flux in a two-state channel model.
• To determine if the blocking effect of side chains diminishes with increased fluctuation rates.

Main Methods:

• Utilized a continuum diffusion model for a two-state, three-dimensional cylindrical channel.
• Simulated random transitions between open and blocked channel states.
• Analyzed solute dynamics and conformational fluctuation timescales.

Main Results:

• The simple relationship between average flux and state-specific fluxes breaks down when fluctuation and solute dynamics timescales are comparable.
• The blocking effect of a side chain decreases as the rate of conformational fluctuations increases.
• This reduction in blocking is independent of blockage degree and probability.

Conclusions:

• Increased side chain fluctuation rates enhance solute transport through protein channels.
• The "closed" states observed in structural studies may still allow solute transport.
• Dynamic fluctuations play a critical, often underestimated, role in channel permeability.