Proteins microstates

Common Properties of Solute and Temperature Effects Shifting the Ensemble of Protein Microstates... 

Figure 1.6 Schematic representation of the changes in protein conformational microstate distribution that attend ligand (i.e., substrate, transition state, product and inhibitor) binding during enzyme catalysis. For each step of the reaction cycle, the distribution of conformational microstates is represented as a potential energy (PE) diagram.

If microstates lead to the existence of a distribution of energies of interaction between aromatic groups and neighboring groups of atoms, then the individual spectra of these groups in different microstates shift differently, which results in an inhomogeneous contour of the absorption band. The application of selective photoexcitation permits specific effects of the distribution of microstates on spectral, temporal, and polarization fluorescence properties to be observed. 221 Such effects have been observed in studies of proteins, 1,8) and, as we show below, they may be used to obtain important information on dynamics. 

Both the denaturation process in proteins and the melting transition (also referred to as the helix-to-coil transition) in nucleic acids have been modeled as a two-state transition, often referred to as the all-or-none or cooperative model. That is, the protein exists either in a completely folded or completely unfolded state, and the nucleic acid exists either as a fully ordered duplex or a fully dissociated monoplex. In both systems, the conformational flexibility, particularly in the high-temperature form, is great, so that numerous microstates associated with different conformers of the biopolymer are expected. However, the distinctions between the microstates are ignored and only the macrostates described earlier are considered. For small globular proteins and for some nucleic acid dissociation processes,11 the equilibrium between the two states can be represented as... 

In molecular systems, storage of a certain sequence of nucleotides (amount of stored information Imax) depends mainly on the chemical sta bility of the DNA molecule. The information capacity is determined by the number of certain combinations of nucleotides but not by the number of microstates, including accounting the vibrations of aU of the atoms in the DNA chain. The formation of macroinformation is coupled here with the work and energy consumption in the course of biosynthesis of the DNA molecule. Similarly, the information can be implemented by con suming energy for the processes of the information translation and synthe sis of the protein chain. 

A/f° is endothermic. Heat must be added to denature the protein. Denaturation leads to more disorder (an increase in microstates). The magnitude of AS° is fairly large (1600 J/K-mol). Proteins are large molecules and therefore denatmation would lead to a large increase in microstates. The temperature at which the process favors the denatured state can be calculated by setting AG° equal to zero. 

Sillen, A., Hennecke, J., Roethlisberger, D., Glockshuber, R., Engelborghs, Y. Fluorescence quenching in the DsbA protein from Escherichia coli complete picture of the excited-state energy pathway and evidence for the reshuffling dynamics of the microstates of tryptophan. Protein Sci. 37, 253-263 (1999)... 

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