Size Sensitivity of Metabolite Diffusion in Macromolecular Crowds

Area of Science:

• Biophysics
• Cellular Biology
• Physical Chemistry

Background:

• Metabolite diffusion is vital for cellular functions but poorly understood in crowded cellular environments.
• Conflicting reports exist regarding diffusion behavior in cells, necessitating further investigation.

Purpose of the Study:

• To investigate the diffusion of nano- and subnanometer-sized tracers in crowded environments.
• To elucidate the relationship between tracer size, crowding, and diffusion dynamics.

Main Methods:

• Utilized pulsed-gradient stimulated-echo Nuclear Magnetic Resonance (NMR).
• Employed Brownian and Stokesian dynamics simulations.
• Used Ficoll as a crowding agent and simulated diffusion in E. coli cytoplasm.

Main Results:

• Observed a linear decrease in tracer diffusivity with increasing occupied volume fraction up to 30-40%.
• Simulations indicated a linear correlation between diffusivity slowdown and particle size.
• Experimental data suggested a more complex relationship, potentially due to crowder porosity.

Conclusions:

• Diffusion slowdown in crowded environments is influenced by particle size and volume fraction.
• Discrepancies between simulation and experimental results highlight the complexity of intracellular diffusion.
• Results contribute to understanding nanoviscosity and intracellular transport.