Universal relation between instantaneous diffusivity and radius of gyration of proteins in aqueous solution

TL;DR

This study reveals a universal relation linking the instantaneous diffusivity of proteins to their radius of gyration, showing that conformational fluctuations directly influence diffusion in aqueous solutions.

Contribution

It demonstrates that a local Stokes-Einstein relation accurately describes the connection between diffusivity and radius of gyration across various proteins.

Findings

Radius of gyration exhibits 1/f fluctuations synchronized with diffusivity.

The local Stokes-Einstein relation D_I ∝ 1/(R_g + R_0) holds for different proteins.

The relation is a general property for proteins with varying conformational fluctuation strengths.

Abstract

Protein conformational fluctuations are highly complex and exhibit long-term correlations. Here, molecular dynamics simulations of small proteins demonstrate that these conformational fluctuations directly affect the protein's instantaneous diffusivity $D_I$. We find that the radius of gyration $R_g$ of the proteins exhibits $1/f$ fluctuations, that are synchronous with the fluctuations of $D_I$. Our analysis demonstrates the validity of the local Stokes-Einstein type relation $D_I\propto1/(R_g + R_0)$, where $R_0\sim0.3$ nm is assumed to be a hydration layer around the protein. From the analysis of different protein types with both strong and weak conformational fluctuations the validity of the Stokes-Einstein type relation appears to be a general property.