Salt-Induced Universal Slowing Down of the Short-Time Self-Diffusion of a Globular Protein in Aqueous Solution

Abstract

The short-time self-diffusion D of the globular model protein bovine serum albumin in aqueous (D2O) solutions has been measured comprehensively as a function of the protein and trivalent salt (YCl3) concentration, noted c(p) and c(s), respectively. We observe that D follows a universal master curve D(c(s),c(p)) = D(c(s) = 0,c(p)) g(c(s)/c(p)), where D(c(s) = 0,c(p)) is the diffusion coefficient in the absence of salt and g(c(s)/c(p)) is a scalar function solely depending on the ratio of the salt and protein concentration. This observation is consistent with a universal scaling of the bonding probability in a picture of cluster formation of patchy particles. The finding corroborates the predictive power of the description of proteins as colloids with distinct attractive ion-activated surface patches.