Physics of Proteins at Low Temperature

Abstract

We present results of a hole burning study with thermal cycling and waiting time spectral diffusion experiments on a modified cytochrome - c protein in its native as well as in its denatured state. The experiments show features which seem to be characteristic for the protein state of matter and its associated dynamics at low temperature. The properties responsible for the observed patterns are organisation paired with randomness and, in addition, the finite size which gives rise to surface and solvent effects. We discuss some general model approaches which might serve as guide lines for understanding these features.Comment: To Appear in the Journal of Low Temperature Physics, 200

Spectroscopy of proteins at low temperature. Part I: Experiments with molecular ensembles

“…In addition, the question as to the dominant coupling between chromophore and environment responsible for spectral diffusion had to be addressed as well: is spectral diffusion in proteins a solvent effect, or is it solely induced by conformational changes in the nearby protein environment, or can both be observed, for instance solvent effects which influence the transitions within the manifold of conformational substates. To check on these questions we performed quite a series of spectral diffusion experiments with a variety of modified heme proteins [18,82]. In heme proteins the chromophore is shielded from the solvent because it is located in the protein interior.…”

“…In single-molecule experiments these frequency fluctuations can be observed directly [16]. In ensemble experiments they show up as time dependent line broadening processes [18]. Measuring these processes, for instance their jump-width distribution, the respective frequency autocorrelation function, the respective temperature dependencies, etc., yield information on specific features of the energy landscape.…”

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

“…Aging dynamics, too, follows a power law, r / t Àb a , and, again, b is of the same magnitude for all proteins investigated, namely 0.07. Several models have been proposed to account for the seemingly universal features of the power law exponents a and b [22][23][24]. We also stress that there are severe solvent effects as far as the absolute magnitude of the spectral diffusion broadening is concerned [25], despite the local character of the probe.…”

Modeling study of non-line-narrowed hole-burned spectra in weakly coupled dimers and multi-chromophoric molecular assemblies

“…As discussed in Section 1, single-molecule spectroscopy has revealed that the magnitude of observed site energy 'jumps' may vary widely from quite large (on the order of hundreds of cm À1 , although still essentially within the pre-burn SDF) to very small (on the order of a few cm À1 ) [17,18]. A complete consideration of various tier of the protein energy landscape is beyond the scope of this manuscript, but we wish to note here only that the effects of small jumps on non-resonant HB spectra are expected to be rather small except in cases of strongly non-degenerate distribution functions (unpublished observations) where, due to the extremely low apparent HB efficiency, any change in photoproduct distribution is likely to produce significant changes in the HB spectrum (as just discussed regarding photoproduct shifts).…”

“…Single-molecule spectroscopy has revealed that there are very large spectral jumps of the order of inhomogeneous broadening (C inh ), as well as very small (more probable) spectral jumps (especially in protein systems) and jumps on an intermediate level, each type of jump evidently reflecting different tiers of the energy landscape (see Refs. [17,18], and references therein).…”