Simulation of the ligand-leaving process of the human heat shock protein.

The human heat shock protein plays a critical role in various diseases and is an important target for pharmacological modulation. Simulation of conformational changes and free energy profiles of the human heat shock protein derived by the ligand-leaving process is a challenging issue. In this work, steered molecular dynamics simulation was adopted to simulate the ligand-leaving process. Two composite systems of heat shock protein NHSP90 and small molecules 6FJ and 6G7 are selected as research objects. The free energy during the leaving of ligand small molecules is calculated using conventional molecular dynamics simulation, steered molecular dynamics simulation (SMD), and the umbrella sampling method. We found that the a slower pulling velocity (0.001 nm ns-1) will result in 2.19 kcal mol-1, and the umbrella sampling method gives a value of 3.26 kcal mol-1 for the free energy difference for the two systems, which reasonably agrees with experimental results. A faster-pulling velocity (0.01 nm ns-1) leads to a large overestimation of free energy. At the same time, the conformational analysis indicated that the faster pulling velocity may lead to the conformational change of NHSP90, which was proved to be false by the slower pulling velocity and the umbrella sampling method.

Molecular mechanism of methyl-dependent and spatial-specific DNA recognition of c-Jun homodimer.

DNA methylation is important in regulation of gene expression and normal development because it alters the interplay between protein and DNA. Experiments have shown that a single 5-methylcytosine at different CpG sites (mCpG) might have different effects on specific recognition, but the atomistic origin and dynamic details are largely unclear. In this work, we investigated the mechanism of monomethylation at different CpG sites in the cognate motif and the cooperativity of full methylation. By constructing four models of c-Jun/Jun protein binding to the 5[Formula: see text]-XGAGTCA-3[Formula: see text] (X represents C or methylated C) motif, we characterized the dynamics of the contact interface using the all-atom molecular dynamics method. Free energy analysis of MM/GBSA suggests that regardless of whether the C12pG13 site of the bottom strand is methylated, the effects from mC25 of the top strand are dominant and can moderately enhance the binding by [Formula: see text] 31 kcal/mol, whereas mC12 showed a relatively small contribution, in agreement with the experimental data. Remarkably, we found that this spatial-specific influence was induced by different regulatory rules. The influence of the mC25 site is mainly mediated by steric hindrance. The additional methyl group leads to the conformational changes in nearby residues and triggers an obvious structural bending in the protein, which results in the formation of a new T-Asn-C triad that enhances the specific recognition of TCA half-sites. The substitution of the methyl group at the mC12 site of the bottom strand breaks the original H-bonds directly. Such changes in electrostatic interactions also lead to the remote allosteric effects of protein by multifaceted interactions but have negligible contributions to binding. Although these two influence modes are different, they can both fine-tune the local environment, which might produce remote allosteric effects through protein-protein interactions. Further analysis reveals that the discrepancies in these two modes are primarily due to their location. Moreover, when both sites are methylated, the major determinant of binding specificity depends on the context and the location of the methylation site, which is the result of crosstalk and cooperativity.