Structural influence of the conserved Hsp40 HPD tripeptide on Hsp70 chaperone function

The control of Hsp70 functions has been related to the modulation of ATP hydrolysis and substrate capture by Hsp40. Structural and biophysical analyses of Hsp40 variants and their interactions with Hsp70 have identified key residues for this functional control mechanism. Conserved residues in both Hsp40 and Hsp70 have revealed conserved interactions that link Hsp40 binding to the catalytic residues within Hsp70. The current work investigates the effect of documented J-domain dysfunctional mutations (i.e. D35N, H33Q) on the described interaction linkage. Molecular dynamics simulations were used to compare the persistence of individual bond types (i.e. H-bonds, salt bridges, hydrophobic interactions) between Hsp70 and the bound forms of functional and dysfunctional Hsp40 variants. The generated data suggests the involvement of both direct and allosteric effects for the tested mutations. The observed changes relate mutations in the conserved HPD tripeptide of Hsp40 to alterations in the interaction network that induces Hsp70 chaperone functions. STATEMENT OF SIGNIFICANCEThe significance of the work may be summarized as follows. First, the interaction network for the simulated systems were observed to be different from one previously proposed for a disulfide linked complex (9). This may be attributed to altered residue movement and interactions without the restrictions set by the disulfide link. These results support the use of in silico methods to refine investigations of molecular contacts, particularly for systems, whose in vitro structural elucidation are difficult to achieve without modifications. Second, key interactions for intermolecular and intramolecular contacts were observed within a short simulation time (0.1 ns) matched those from much longer runs (500 ns) (4). This result highlights the possibility of identifying key interactions with relatively low computational cost.