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 dynamics in the deeply supercooled regime (T= 180 K), which is typically not accessible through equilibrium
methods. The observed stimulated dynamic response is attributed to
collective stress–relaxation as the system transitions from
a jammed granular state to an elastically driven regime. The relaxation
time constants exhibit Arrhenius temperature dependence upon cooling
with a minimum in the Kohlrausch–Williams–Watts exponent
atT= 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 normalized
variance χT. The amplification of
fluctuations is consistent with previous studies of hydrated proteins,
which indicate the key role of density and enthalpy fluctuations in
hydration water. Our study provides new insights into X-ray stimulated
stress–relaxation and the underlying mechanisms behind spatiotemporal
fluctuations in biological granular materials.