PDBsum entry 2aa5

Transcription

PDB id

2aa5

Contents

			Protein chains

					255 a.a.

			Ligands

					STR ×2

			Waters ×254

References listed in PDB file

Key reference

Title

A ligand-Mediated hydrogen bond network required for the activation of the mineralocorticoid receptor.

Authors

R.K.Bledsoe, K.P.Madauss, J.A.Holt, C.J.Apolito, M.H.Lambert, K.H.Pearce, T.B.Stanley, E.L.Stewart, R.P.Trump, T.M.Willson, S.P.Williams.

Ref.

J Biol Chem, 2005, 280, 31283-31293. [DOI no: 10.1074/jbc.M504098200]

PubMed id

15967794

Abstract

Ligand binding is the first step in hormone regulation of mineralocorticoid receptor (MR) activity. Here, we report multiple crystal structures of MR (NR3C2) bound to both agonist and antagonists. These structures combined with mutagenesis studies reveal that maximal receptor activation involves an intricate ligand-mediated hydrogen bond network with Asn770 which serves dual roles: stabilization of the loop preceding the C-terminal activation function-2 helix and direct contact with the hormone ligand. In addition, most activating ligands hydrogen bond to Thr945 on helix 10. Structural characterization of the naturally occurring S810L mutant explains how stabilization of a helix 3/helix 5 interaction can circumvent the requirement for this hydrogen bond network. Taken together, these results explain the potency of MR activation by aldosterone, the weak activation induced by progesterone and the antihypertensive agent spironolactone, and the binding selectivity of cortisol over cortisone.



	Figure 3. FIG. 3. Crystal structure of MR LBD bound to aldosterone and progesterone. A, the overall fold of MR is very similar to the other steroid receptors. B, helix 3 (magenta) residues Asn770 and Ser767 form hydrogen bonds (yellow dashed lines) with the loop (green) residue Glu955 preceding the AF-2 (red). Thr945 present on helix 10 (orange) plays a key role in receptor activation by hydrogen bonding to the C-20 carbonyl and C-21 hydroxyl of aldosterone (yellow). C, close-up view of MR-aldosterone hydrogen bond network. The 18-OH is positioned for hydrogen bonding (yellow dashed lines) with the Asn770 carbonyl, whereas the Asn770 amide remains in position for hydrogen bonding to the C-21 OH of aldosterone and Glu955, which lies in the loop preceding the AF-2. Thr945, present on helix 10, forms a pair of hydrogen bonds with the C-20 and C-21 substituents of aldosterone. Cysteine 942 is in position to interact with the 18-OH group to give aldosterone three potential hydrogen bonds to helix 10. D, progesterone makes no hydrogen bonds to Asn770. Multiple orientations of the Thr945 side chain hydroxyl were observed (A and B) in both noncrystallographically related molecules. When the Thr945 side chain hydroxyl is in the B position (green), the distance (black dashed line) to the progesterone C-20 carbonyl makes hydrogen bonding between the ligand and Thr945 unlikely.		Figure 5. FIG. 5. Close-up views of the MR C808S/S810L mutant bound to progesterone, cortisone, and spironolactone. A, an overlay of progesterone (yellow) in MR C808S (cyan) and progesterone (pink) in MR C808S/S810L (pink) binding pockets indicates that the S810L mutation has no measurable effect on ligand position or orientation. Hydrogen bonding networks (yellow dashed lines) are indicated. Van der Waals interactions are indicated by black dashed lines. Multiple orientations of the Thr945 side chain hydroxyl were observed (A and B) in both noncrystallographically related molecules. B, the C-11 carbonyl of cortisone (blue) does not interact with MR C808S/S810L (orange) residue Asn770 and is 2.9 Å away from the backbone carbonyl of Leu769. C, the lactone keto group of spironolactone (white) is 3.7 Å away from Asn770 in MR C808S/S810L (magenta), suggesting a weakened potential for hydrogen bonding to Asn770. Again, multiple orientations of the Thr945 side chain hydroxyl were observed (A and B) in both noncrystallographically related molecules. Similar to that observed with progesterone, the distance from the hydroxyl of Thr945 to the lactone keto moiety of spironolactone differs depending upon the orientation of this residue. The weak interaction of spironolactone with both Asn770 and Thr945 is probably the basis for the antagonism observed with this steroid.

PROCHECK

	Headers