Structural Evidence for Ligand Specificity in the Binding Domain of the Human Androgen Receptor

Abstract

The crystal structures of the human androgen receptor (hAR) and human progesterone receptor ligandbinding domains in complex with the same ligand metribolone (R1881) have been determined. Both threedimensional structures show the typical nuclear receptor fold. The change of two residues in the ligandbinding pocket between the human progesterone receptor and hAR is most likely the source for the specificity of R1881 to the hAR. The structural implications of the 14 known mutations in the ligand-binding pocket of the hAR ligand-binding domains associated with either prostate cancer or the partial or complete androgen receptor insensitivity syndrome were analyzed. The effects of most of these mutants could be explained on the basis of the crystal structure. Androgen (AR)1 and progesterone receptors (PR) are members of the superfamily of nuclear receptors that includes the steroid receptors, among others, as well as the vitamin D, thyroid, retinoic acid receptors, and the so-called orphan receptors. In addition, AR and PR are members of a group of four closely related steroid receptors including the mineralocorticoid receptor and the glucocorticoid receptor recognizing the same hormone response element. In general, steroid receptors are comprised of five to six domains and act as ligand-activated transcription factors that control the expression of specific genes. To date, no experimentally determined three-dimensional structure is available for a complete receptor. During the past few years, x-ray structures have been published for two of the domains, the DNA-binding domain as well as for a number of ligand-binding domains (LBD) including LBD⅐ligand complexes of the estrogen receptor ␣ and ␤, the PR, the vitamin D receptor, the retinoic acid receptors (X,RXR; acid, RAR), the thyroid hormone receptor, and the peroxisome proliferatoractivated receptors (1-13). Despite the low sequence homology of as low as 20% between the LBDs of different nuclear receptor families, all these proteins share a similar fold. They are comprised of up to 12 helices and a small ␤-sheet arranged in a so-called ␣-helical sandwich, a kind of fold that up to now has only been observed for the LBDs of nuclear receptors. Depending on the nature of the bound ligand, agonist, or antagonist, the carboxyl-terminal helix H12 is found in either one of two orientations. In the agonist-bound conformation, helix H12 serves as a "lid" to close the ligand-binding pocket (LBP), whereas in the antagonist-bound conformation helix H12 is positioned in a different orientation thus opening the entrance to the LBP.Androgens and their receptors play an important role in male physiology and pathology.

Crystallization of protein–ligand complexes

“…In all of these cases, coexpression with a high-affinity ligand was key to obtaining protein for structural studies Matias et al, 2000;Sack et al, 2001;He et al, 2004;Madauss et al, 2004;Fig. 1 Hassell et al…”

A Ligand-Based Approach To Identify Quantitative Structure−Activity Relationships for the Androgen Receptor

“…N705S mutants observed in complete androgen insensitivity syndrome (CAIS) corroborate the importance of this interaction. 16 This area overlaps the 17-position of steroids. 11 Poujol et al 10 demonstrated near complete loss of the antagonist properties of hydroxyflutamide and bicalutamide in the N705A mutation, while RU486 and cyproterone acetate maintained the ability to repress transcriptional activation.…”

“…Mutations of ARG752 (e.g., R752Q mutants observed in partial androgen insensitivity syndrome (PAIS)) result in loss of this interaction and poor binding affinity. 16 The blue contour bordering the chiral hydroxyl group of bicalutamide analogues indicates the interaction with ASN705. This amino acid is also important for ligand discrimination and binding.…”

Androgen Receptor Mutations Associated with Androgen Insensitivity Syndrome: A High Content Analysis Approach Leading to Personalized Medicine

“…That NC-TDI recovery was only partial and liganddependent in F764L was surprising. This observation may be related to the fact that F764 makes direct ligand contact [37], and its replacement by ligand may alter the conformation of the ligand binding pocket which results in increased affinity for ligands other than DHT. The R840C mutation demonstrated increased NC-TDI's with all ligands and concentrations tested compared to wild type.…”