Functional Probing of the Human Glucocorticoid Receptor Steroid-interacting Surface by Site-directed Mutagenesis

U. Lind,P. Greenidge,M. Gillner,K. Koehler,A. Wright,J. Carlstedt-Duke

Published 2000 in Journal of Biological Chemistry

ABSTRACT

To elucidate which amino acids in the glucocorticoid receptor ligand-binding domain might be involved in determining steroid binding specificity by interaction with the D-ring of glucocorticoids, we have performed site-directed mutagenesis of the four amino acids Met-560, Met-639, Gln-642, and Thr-739 based on their proximity to the steroid in a model structure. Mutations of these residues affected steroid binding affinity, specificity, and/or steroid-dependent transactivation. The results indicate that these residues are located in close proximity to the ligand and appear to play a role in steroid recognition and/or transactivating sensitivity, possibly by changes in the steroid-dependent conformational change of this region, resulting in the formation of the AF-2 site. Mutation of Gln-642 resulted in a marked decrease in affinity for steroids containing a 17α-OH group. This effect was alleviated by the presence of a 16α-CH3 group to a varying degree. Thr-739 appears to form a hydrogen bond with the 21-OH group of the steroid, as well as possibly forming hydrophobic interactions with the steroid. Met-560 and Met-639 appear to form hydrophobic interactions with the D-ring of the steroid, although the nature of these interactions cannot be characterized in more detail at this point.

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