Protein Crowding and Cholesterol Increase Cell Membrane Viscosity in a Temperature Dependent Manner

Area of Science:

• Biophysics
• Computational Biology
• Materials Science

Background:

• Shear viscosity of lipid membranes governs molecular movement and diffusion-limited reaction rates within cellular membranes.
• Biomembrane heterogeneity suggests cells can regulate these rates by altering local viscosities.
• Experimental determination of membrane viscosity is challenging and prone to errors.

Purpose of the Study:

• To extract shear viscosities of lipid membranes using molecular dynamics simulations.
• To systematically investigate the influence of protein crowding, cholesterol concentration, lipid acyl chain properties, and temperature on membrane viscosity.
• To provide a comprehensive dataset of membrane viscosity values for predicting diffusion coefficients.

Main Methods:

• Utilized a variety of equilibrium methods for extracting shear viscosity from molecular dynamics simulations.
• Performed both coarse-grained and all-atom simulations.
• Systematically varied parameters including protein crowding, cholesterol concentration, lipid acyl chain length and saturation, and temperature.

Main Results:

• Protein concentration, cholesterol concentration, and temperature significantly affect membrane viscosity within physiological ranges.
• Lipid acyl chain length and unsaturation level have a less pronounced effect on membrane viscosity.
• Protein crowding substantially impacts membrane shear viscosity and subsequent diffusion within membranes.

Conclusions:

• Molecular dynamics simulations offer a viable alternative to experimental methods for determining membrane viscosity.
• The collected viscosity data can be used to predict diffusion coefficients using the Saffman-Delbrück model.
• Current molecular dynamics force fields may require refinement for accurate bilayer dynamics description, necessitating finite-size effect corrections for simulation data compared to experiments.