Coherent X-ray Scattering Reveals Nanoscale Fluctuations in Hydrated Proteins

TL;DR

This study uses X-ray Photon Correlation Spectroscopy to explore nanoscale stress relaxation and fluctuations in hydrated proteins at very low temperatures, revealing temperature-dependent dynamics and heterogeneity.

Contribution

It introduces a novel application of XPCS to probe deeply supercooled hydrated proteins, uncovering nanoscale fluctuation mechanisms not accessible by traditional methods.

Findings

Nanoscale stress relaxation exhibits Arrhenius temperature dependence.

Maximum dynamical heterogeneity occurs at 227 K.

Enhanced fluctuations are observed in two-time correlation functions.

Abstract

Hydrated proteins undergo a transition in the deeply supercooled regime, which is attributed to rapid changes in hydration water and protein structural dynamics. Here, we investigate the nanoscale stress relaxation in hydrated lysozyme proteins stimulated and probed by X-ray Photon Correlation Spectroscopy (XPCS). This approach allows us to access the nanoscale dynamic response in the deeply supercooled regime (T = 180 K) which is typically not accessible through equilibrium methods. The relaxation time constants exhibit Arrhenius temperature dependence upon cooling with a minimum in the Kohlrausch-Williams-Watts exponent at T = 227 K. The observed minimum is attributed to an increase in dynamical heterogeneity, which coincides with enhanced fluctuations observed in the two-time correlation functions and a maximum in the dynamic susceptibility quantified by the normalised variance $\chi_T$. Our study provides new insights into X-ray stimulated stress relaxation and the underlying mechanisms behind spatio-temporal fluctuations in biological granular materials.