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Properties of a simple model of polypeptide chains were studied by the means of the Monte Carlo method. The chains were built on the (310) hybrid lattice. The residues inter­acted with long-range potential. There were two kinds of residues: hydrophobic and hy- drophilic forming a typical helical pattern -HHPPHPP-. Short range potential was used to prefer helical conformations of the chain. It was found that at low temperatures the model chain formes dense and partially ordered structures (non-unique). The presence of the lo­cal potential led to an increase of helicity. The effect of the interplay between the two po­tentials was studied. After the collapse of the chain further annealing caused rearrange­ment of helical structures. Dynamic properties of the chain at low temperature depended strongly on the local chain ordering.
A number of factors at all stages of data processing which affect the accuracy of determination of 15N relaxation parameters in 15N-labeled proteins is discussed. Methods which allow to improve accuracy of the determined parameters are presented using data obtained for Cucurbita maxima trypsin inhibitor.
Several points seem essential for construction of the future statistical theory of biochemical processes. (a) The native proteins involved in these processes reveal a purely stochastic intramolecular dynamics of conformational transitions much slower than the usual vibrational dynamics. At least in the range from 10-11 to 10-7s the relaxation time spectrum of conformational transition dynamics is practically quasi-continuous. (b) The majority of reactions involving proteins are controlled and, presumably, also gated by this stochastic dynamics. (c) Of special importance is the short initial-condition dependent stage of biochemical reactions, neglected in the description of the reaction in terms of the standard kinetics. This stage is directly observed in experiments in which especially prepared initial conformational substates of the protein are confined to the reaction transition state. (d) The initial-condition dependent stage, and not that described by the standard kinetics, is responsible for the coupling of component reactions in the complete catalytic cycles proceeding in the steady-state and more complex processes of biological free energy transduction.
A high coordination lattice discretization of protein conformational space is described. The model allows discrete representation of polypeptide chains of globular proteins and small macromolecular assemblies with an accuracy comparable to the accuracy of crystallographic structures. Knowledge based force Held, that consists of sequence specific short range interactions, coopera­tive model of hydrogen bond network and tertiary one body, two body and multibody interactions, is outlined and discussed. A model of stochastic dy­namics for these protein models is also described. The proposed method enables moderate resolution tertiary structure prediction of simple and small globular proteins. Its applicability in structure prediction increases significantly when evolutionary information is exploited or/and when sparse experimental data are available. The model responds correctly to sequence mutations and could be used at early stages of a computer aided protein design and protein redesign. Computational speed, associated with the discrete structure of the model, enables studies of the long time dynamics of polypeptides and proteins and quite detailed theoretical studies of thermodynamics of nontrivial protein models.
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