Determinants of spironolactone binding specificity in the mineralocorticoid receptor (original) (raw)
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Molecular Pharmacology, 2000
Sequence analysis revealed a strong homology between the ligand-binding domain (LBD) of the human mineralocorticoid receptor (hMR) and glucocorticoid receptor (hGR). Nevertheless, steroids with bulky C11-substituents bind to hGR, unlike hMR. In this report, a mutant hMR, in which the residue Ala-773 facing the C11 steroid position was replaced by a glycine (A773G), was assayed for its capacity to bind steroids, to interact with receptor coactivators, and to stimulate transcription. The capacity of A773G to bind aldosterone and C11substituted spirolactones was the same as that of the wild-type receptor. The agonist properties of aldosterone, as well as the antagonist feature of compounds bearing a 11-allenyl group and a C17-ketone function, remain unchanged. In contrast, C11-substituted steroids with a 17␥-lactonic ring displayed antagonist properties with hMR and acted as potent agonists with A773G. An agonist-dependent hMR interaction with SRC-1 was observed for both the wild-type and the mutant receptors. The hMR activation process is discussed in the light of the hMR-LBD homology model based on the structural data of the human progesterone receptor LBD.
Clinical and Experimental Pharmacology and Physiology, 2004
The importance of mineralocorticoid receptor (MR) antagonists in the treatment of cardiovascular disease has been emphasised by two recent clinical trials, one using spironolactone and the other using a new selective MR antagonist, namely eplerenone. Eplerenone has a very low affinity for the glucocorticoid receptor (GR). Determinants of binding specificity of eplerenone to the MR were investigated using chimeras created between the ligand-binding domains (LBD) of the MR and the GR. These chimeras had been used previously to investigate aldosterone and spironolactone binding specificity to the MR. Eplerenone competed strongly for [(3)H]-dexamethasone binding to a MR/GR chimera containing amino acids 804-874 of the MR and weakly to a chimera containing amino acids 672-803 of the MR. Within the 804-874 region, eplerenone competed for [(3)H]-dexamethasone binding to a chimera containing amino acids 820-844 of the MR, although the calculated affinity was approximately 10-fold lower than for binding to the full-length MR LBD. Similar results were obtained using another MR antagonist, namely spironolactone. Modelling of eplerenone binding to the MR LBD, based on the GR LBD crystal structure, suggests that amino acids 820-844 affect the overall shape of the ligand-binding pocket and that eplerenone acts as an MR antagonist because it fails to stabilize the active conformation of the receptor. In contrast with results with the MR antagonists eplerenone and spironolactone, amino acids 820-844 are sufficient in themselves to confer high-affinity aldosterone binding to the MR, suggesting that the binding determinants of the two antagonists are similar to each other but differ from those of aldosterone.
Biochimica et Biophysica Acta (BBA) - Molecular Cell Research, 2002
The alkylation of amino groups of the mineralocorticoid receptor (MR) with pyridoxal 5P-phosphate or 2,4,6trinitrobenzenesulphonate (TNBS) under controlled conditions modifies only one lysyl residue, which accounts for a 70% inhibition of steroid binding capacity. The K d of aldosterone for MR is not affected by the treatment, but the total number of binding sites is greatly decreased. The modified receptor is capable of dynamically conserving its association with the hsp90based heterocomplex. Importantly, the binding of natural agonists protects the hormone binding capacity of the MR from the inactivating action of alkylating agents. In contrast, antagonistic steroids are totally incapable of providing such protection. Like the antagonistic ligands, and despite its potent mineralocorticoid biological effect, the sole MR specific synthetic agonist known to date, 11,19-oxidoprogesterone (11-OP), shows no protective effect upon treatment of the MR with pyridoxal 5P-phosphate or TNBS. Limited digestion of the MR with K-chymotrypsin generates a 34 kDa fragment, which becomes totally resistant to digestion upon binding of natural agonists, but not upon binding of antagonists. Interestingly, the synthetic 21-deoxypregnanesteroid 11-OP exhibits an intermediate pattern of proteolytic degradation, suggesting that the conformational change generated in the MR is not equivalent to that induced by antagonists or natural agonists. We conclude that in the first steps of activation, the MR changes its conformation upon binding of the ligand. However, the nature of this conformational change depends on the nature of the ligand. The experimental evidence shown in 0167-4889 / 02 / $^see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 -4 8 8 9 ( 0 1 ) 0 0 1 8 4 -7 this work suggests that a single lysyl group can determine the hormone specificity of the MR. ß
Structural Determinants of Aldosterone Binding Selectivity in the Mineralocorticoid Receptor
Journal of Biological Chemistry, 1999
The structural determinants of aldosterone binding specificity in the mineralocorticoid receptor (MR) have not been determined. The MR has greatest sequence identity with the better characterized glucocorticoid receptor (GR), which is reflected in their overlapping ligand binding specificities. There must be subtle sequence differences that can account for the MR-specific binding of aldosterone and the shared binding of cortisol. To characterize ligand binding specificity, chimeras were made between the human MR and GR ligand-binding domains (LBDs). Three points were chosen as break points to generate a total of 16 different constructs.
Molecular Endocrinology, 2007
The amino acids that confer aldosterone binding specificity to the mineralocorticoid receptor (MR) remain to be determined. We had previously analyzed a panel of chimeras created between the MR and the glucocorticoid receptor and determined that amino acids 804-874 of the MR ligand binding domain are critical for aldosterone binding. In the present study a further series of chimeras was created within this region. The chimeras were analyzed by a transactivation assay and [ 3 H]aldosterone binding, and the critical region was narrowed down to amino acids 820-844. Site-directed mutagenesis was used to create single and multiple amino acid substitutions in this region. These studies identified 12 of the 16 amino acids that differ in the MR and the glucocorticoid receptor in this region as being critical to conferring aldosterone responsivity. The amino acids that differ in the region First
Mechanisms of ligand specificity of the mineralocorticoid receptor
Journal of Endocrinology
The mineralocorticoid receptor (MR) differs from the other steroid receptors in that it responds to two physiological ligands, aldosterone and cortisol. In epithelial tissues, aldosterone selectivity is determined by the activity of 11β-hydroxysteroid dehydrogenase type 2, while in other tissues, including the heart and regions of the central nervous system, cortisol is the primary ligand for the MR where it may act as an antagonist. Clinical trials have demonstrated the potential of MR antagonists in the treatment of cardiovascular disease, though their use has been limited by concurrent hyperkalaemia. In order to better target the MR, an understanding of the structural determinants of tissue- and ligand-specific MR activation is needed. Interactions of the MR have been identified, which exhibit ligand discrimination and/or specificity. These interactions include those of the ligand-binding domain with ligand, with the N-terminal domain and with putative co-regulatory molecules. Ag...
Molecular Pharmacology
In humans, spironolactone and mespirenone are well known antimineralocorticoids without C-11 substituents. These compounds display antagonist properties by acting through the human androgen receptor (hAR). In contrast, we demonstrate here that synthetic mineralocorticoid antagonists bearing hydrophobic C-11 substituents and C-17␥-lactone are potent hAR agonists in vitro. The three-dimensional construction of both the ligand binding domain (LBD) of the hAR and the human mineralocorticoid receptor (hMR), based on the crystal structure of the LBD of the human progesterone receptor, revealed not only that the interactions with the steroidal A-and D-rings seemed to be crucial for stabilization of active hMR or hAR conformation, but that other steroidal substitutions could influence the agonist versus antagonist activity of ligands. The docking of synthetic compounds bearing C-11 hydrophobic
Molecular Endocrinology, 2010
The mineralocorticoid receptor (MR) binds the steroid hormones aldosterone and cortisol and has an important physiological role in the control of salt homeostasis. Regions of the protein important for gene regulation have been mapped to the amino-terminal domain (NTD) and termed activation function (AF)1a, AF1b, and middle domain (MD). In the present study, we used a combination of biophysical and biochemical techniques to investigate the folding and function of the MR-NTD transactivation functions. We demonstrate that MR-AF1a and MR-MD have relatively little stable secondary structure but have the propensity to form α-helical conformation. Induced folding of the MR-MD enhanced protein-protein binding with a number of coregulatory proteins, including the coactivator cAMP response element-binding protein-binding protein and the corepressors SMRT and RIP140. By contrast, the MR-AF1b domain appeared to have a more stable conformation consisting predominantly of β-secondary structure. F...
Molecular endocrinology, 2009
The mineralocorticoid receptor (MR) plays a central role in electrolyte homeostasis and in cardiovascular disease. We have previously reported a ligand-dependent N/C-interaction in the MR. In the present study we sought to fully characterize the MR N/C-interaction. By using a range of natural and synthetic MR ligands in a mammalian two-hybrid assay we demonstrate that in contrast to aldosterone, which strongly induces the interaction, the physiological ligands deoxycorticosterone and cortisol weakly promote the interaction but predominantly inhibit the aldosterone-mediated N/C-interaction. Similarly, progesterone and dexamethasone antagonize the interaction. In contrast, the synthetic agonist 9alpha-fludrocortisol robustly induces the interaction. The ability of the N/C interaction to discriminate between MR agonists suggests a subtle conformational difference in the ligand-binding domain induced by these agonists. We also demonstrate that the N/C interaction is not cell specific, c...
Bioorganic & Medicinal Chemistry, 2016
Mineralocorticoid receptor (MR) antagonists continue to be a prevalent area of research in the pharmaceutical industry. Herein we report the discovery of various spirooxindole and dibenzoxazepine constructs as potent MR antagonists. SAR analysis of ourspirooxindole hit led to highly potent compounds containingpolar solubilizing groups, which interact with thehelix-11region of the MR ligand binding domain (LBD). Various dibenzoxazepine moieties were also prepared in an effort to replace a known dibenzoxepanesystem which interacts with the hydrophobicregion of the MR LBD. In addition, an X-ray crystal structure was obtained from a highly potent compound which was shown to exhibit both partial agonist and antagonist modes of action against MR.