Probing cage relaxation in concentrated protein solutions by XPCS

TL;DR

This study demonstrates how XPCS can be effectively used to measure long-time protein diffusion in crowded solutions, addressing radiation damage issues to advance understanding of cellular protein dynamics.

Contribution

The paper introduces an experimental and analytical approach enabling XPCS measurements of protein cage relaxation in highly concentrated solutions, overcoming radiation damage challenges.

Findings

Successful measurement of cage relaxation in concentrated protein solutions.

Radiation damage depends on dose and dose rate, influencing experimental outcomes.

Strategies to mitigate radiation effects for future biological XPCS studies.

Abstract

Diffusion of proteins on length scales of their own diameter in highly concentrated solutions is essential for understanding the cellular machinery of living cells, but its experimental characterization remains a challenge. While X-ray photon correlation spectroscopy (XPCS) is currently the only technique that in principle allows for a measurement of long-time collective diffusion on these length scales for such systems, its application to protein solutions is seriously hampered by radiation damage caused by the highly intense X-ray beams required for such experiments. Here we apply an experimental design and an analysis strategy that allow us to successfully use XPCS experiments in order to measure collective long-time cage relaxation in highly crowded solutions of the eye lens protein {\alpha}-crystallin close to and beyond dynamical arrest. We also address the problem of radiation-induced damage in such experiments. We demonstrate that radiation effects depend both on the total dose as well as the dose rate of the absorbed radiation, and discuss possible processes and mechanism responsible for the observed radiation effects as well as their consequences for future applications of XPCS in biological systems.