Collective diffusion coefficient of proteins with hydrodynamic, electrostatic and adhesive interactions

TL;DR

This paper develops a theoretical model for the collective diffusion coefficient of interacting protein spheres, incorporating electrostatic, hydrodynamic, and adhesive forces, and compares it with experimental data on lysozyme.

Contribution

It introduces a new simple formula for the first-order correction in the diffusion coefficient based on an effective stickiness parameter, validated against experiments.

Findings

The model accurately predicts the diffusion behavior of lysozyme under various ionic strengths.

Lubrication forces significantly influence the hydrodynamic interactions.

The effective stickiness parameter simplifies complex interactions into a usable form.

Abstract

A theory is presented for lambda_C, the coefficient of the first-order correction in the density of the collective diffusion coefficient, for protein spheres interacting by electrostatic and adhesive forces. An extensive numerical analysis of the Stokesian hydrodynamics of two moving spheres is given so as to gauge the precise impact of lubrication forces. An effective stickiness is introduced and a simple formula for lambda_C in terms of this variable is put forward. A precise though more elaborate approximation for lambda_C is also developed. These and numerically exact expressions for lambda_C are compared with experimental data on lysozyme at pH 4.5 and a range of ionic strengths between 0.05 M and 2 M.