  2H NMR is used to study the mechanisms for the reorientation of protein
hydration water. In the past, crossovers in temperature-dependent correlation
times were reported at T_x1=225K (X1) and T_x2=200K (X2). We show that neither
X1 nor X2 are related to a fragile-to-strong transition. Our results rule out
an existence of X1. Also, they indicate that water performs thermally activated
and distorted tetrahedral jumps at T<T_x2, implying that X2 originates in an
onset of this motion, which may be related to a universal defect diffusion in
materials with defined hydrogen-bond networks.
