Structural fluctuations and aging processes in deeply frozen proteins

Abstract

Frozen proteins are nonergodic systems and are subject to two types of structural motions, namely relaxation and fluctuation. Relaxation manifests itself in aging processes which slow the fluctuations. Within certain approximations we are able to experimentally separate the aging dynamics from the fluctuation dynamics by introducing two time parameters, namely an aging time t a and a waiting time t w . Both processes follow power laws in time. The fluctuation dynamics shows features of universality characterized by a rather uniform exponent of 1 4/ . This universality features were shown to be possible due to a random walk on a 1D random trajectory in conformational phase space. A very interesting aspect of protein dynamics concerns the influence of the host solvent on structural motions of the protein cores. We present results for sugar solvents and discuss possible mechanisms.

Physics of Proteins at Low Temperature

“…The spectral diffusion dynamics in glasses follows logarithmic time laws whereas in proteins power laws with a rather low exponent of order 0.25 were observed. 34 In addition, SD was found to be sensitive to deuteration 33 and, despite the fact that the chromophore was embedded in the interior of the protein, solvent effects did occur. 28,35,36 The question then was how the special features measured could be explained and what kind of protein properties could they reflect.…”

“…28 In addition, an influence of the solvent on the frequency correlation time had to be postulated. 34,35 As a second approach, we present here a model which is based on the presence of TLS, but which takes into account specific features of globular proteins, namely their finite, rather well defined size and the presence of rather spherical interfaces between protein and solvent. We call this approach the "independent low energy surface excitation" model.…”

Hole burning experiments with proteins: Relaxations, fluctuations and glass-like features

“…The main results can be summarized as follows: (i) spectral diffusion dynamics as measured via the time dependent width r of a spectral hole follows a power law in waiting time: r / t a w . For all proteins investigated we found a ffi 0.25, irrespective of the solvent [21,11]. In addition to the waiting time experiments, we performed also aging time experiments.…”

“…The waiting time is the time between burning and reading the hole. Accordingly, aging phenomena reflect solely relaxation processes whereas waiting time phenomena reflect also fluctuation processes [10,11].…”