Structural and dynamic effects of point mutations in the recognition helix of the glucocorticoid receptor DNA-binding domain.

We have studied the wild type and two variants of the glucocorticoid receptor DNA-binding domain (GRDBD): in one variant the three residues (the 'P-box' in GRDBD) that are essential for the discrimination between GREH and EREH are mutated to those in the estrogen receptor DBD (GRDBDega) and the other variant is a point mutation of one P-box residue, Ser459Gly (GRDBDggv). Molecular dynamics simulations (0.5-0.7 ns) have been performed on the GRDBDs, free in solution as well as in complex with the half-site response elements of the glucocorticoid (GREH) and estrogen (EREH) receptors. The residues which are central when forming the protein dimer interface in GRE-(GRDBD)2 (the 'D-box') were found to have different conformations in the different GRDBD-DNA complexes. This is consistent with experimental results showing that the cooperativity of dimeric GRDBD binding to DNA strongly depends on both the response element and the P-box residues. In our simulations the structures of GREH-GRDBDgsv (i.e. wild-type) and GREH-GRDBDggv were more similar to each other than to the respective GRDBDs bound to EREH. This is due to a thymine methyl group which is present in the major groove of the GREH and prevents the first zinc coordinating subdomain in GRDBD to approach GREH, but which is absent in EREH. Thus, EREH-GRDBD is able to respond more to the Ser459Gly mutation than GREH-GRDBD.