PubMed · 12378402
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J E Rabinowitz, R J Samulski. 2002. Vector biophysics: crystal-clear view.. https://doi.org/10.1038/sj.gt.3301884
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Recent results of spectral diffusion experiments by spectral hole-burning techniques carried out at cryogenic temperatures on various monomeric heme proteins unequivocally show interesting new features of conformational dynamics of globular proteins that were not emphasized in the literature until now. These new aspects of the protein dynamics are anomalous diffusion and the aging effect. Here, using the similarities between proteins and glassy systems, we present a model which can interpret the line broadening and-through this effect-the aging phenomenon as well. Leaving untouched the widely accepted energy landscape (EL) concept for the general description of protein dynamics, we concentrate on the bottom of the funnel-like EL, because this part corresponds to the native state(s) at low temperature. We suggest that the overall shape of the EL at the lowest energy range is rather smooth, but on a finer scale it consists of traps. The dynamics is defined by sequential jumps among these traps and the process is described by a Master equation, where the hopping rate only depends on the parameters of the starting state. This model was adapted to interpret the common results of spectral diffusion experiments. We tested our model in the simplest case by computer simulation, and it shows excellent agreement with the experimental data. To our knowledge this is the first work where a theoretical interpretation of the aging dynamics of proteins is directly and quantitatively related to the experimental observations. We also show that the model, after the generalization that the traps are hierarchically organized, is in accordance with the concept of other well-known EL models.
Fluorescence correlation spectroscopy was used to measure the diffusion behavior of a mixture of DMPC or DMPC/DMPG liposomes with human serum albumin (HSA) and mesoporphyrin (MP), which was used as the fluorescent label for liposomes and HSA as well. For decomposing the fluorescence intensity autocorrelation function (ACF) into components corresponding to a liposome population, HSA and MP, we used a maximum entropy procedure that computes a distribution of diffusion times consistent with the ACF data. We found that a simple parametric non-linear fit with a discrete set of decay components did not converge to a stable parameter set. The distribution calculated with the maximum entropy method was stable and the average size of the particles calculated from the effective diffusion time was in good agreement with the data determined using the discrete-component fit.
This review presents an overview of the fluorescence detection and spectroscopy of single molecules (SMS) in liquids and on surfaces under ambient conditions. The various techniques of SMS, such as confocal epifluorescence detection and wide-field imaging are presented and discussed, together with the different methods of data analysis such as fluorescence correlation spectroscopy and burst-by-burst analysis. Selected applications of the various techniques in physics, chemistry, and biology are described.