Development of 7TM receptor-ligand complex models using ligand-biased, semi-empirical helix-bundle repacking in torsion space: application to the agonist interaction of the human dopamine D2 receptor

Marcus Malo,Kristina Luthman,Peder Svensson,Lars Brive,Ronnie Persson

doi:10.1007/s10822-013-9640-z

Abstract

Prediction of 3D structures of membrane proteins, and of G-protein coupled receptors (GPCRs) in particular, is motivated by their importance in biological systems and the difficulties associated with experimental structure determination. In the present study, a novel method for the prediction of 3D structures of the membrane-embedded region of helical membrane proteins is presented. A large pool of candidate models are produced by repacking of the helices of a homology model using Monte Carlo sampling in torsion space, followed by ranking based on their geometric and ligand-binding properties. The trajectory is directed by weak initial restraints to orient helices towards the original model to improve computation efficiency, and by a ligand to guide the receptor towards a chosen conformational state. The method was validated by construction of the β1 adrenergic receptor model in complex with (S)-cyanopindolol using bovine rhodopsin as template. In addition, models of the dopamine D2 receptor were produced with the selective and rigid agonist (R)-N-propylapomorphine ((R)-NPA) present. A second quality assessment was implemented by evaluating the results from docking of a library of 29 ligands with known activity, which further discriminated between receptor models. Agonist binding and recognition by the dopamine D2 receptor is interpreted using the 3D structure model resulting from the approach. This method has a potential for modeling of all types of helical transmembrane proteins for which a structural template with sequence homology sufficient for homology modeling is not available or is in an incorrect conformational state, but for which sufficient empirical information is accessible.Electronic supplementary materialThe online version of this article (doi:10.1007/s10822-013-9640-z) contains supplementary material, which is available to authorized users.

Highlights

The family of monoaminergic G-protein coupled receptors (GPCRs) is well-studied due to their relevance as drug targets
GPCRs are believed to exist in active signaling states stabilized by agonists, and in inactive states stabilized by inverse agonists [1, 2]
Recently have structures of active- or nearactive-state GPCRs in the presence of agonists been determined, achieved using an A2A adenosine receptor— T4L chimera bound to UK432097 [15], thermostabilized A2A adenosine receptors bound to adenosine and NECA [16], or by using fragments of antibodies to stabilize the agonist-bound state of the b2 adrenergic receptor (b2AR) [17, 18]

Summary

Introduction

The family of monoaminergic G-protein coupled receptors (GPCRs) is well-studied due to their relevance as drug targets. Recently have structures of active- or nearactive-state GPCRs in the presence of agonists been determined, achieved using an A2A adenosine receptor— T4L chimera bound to UK432097 [15], thermostabilized A2A adenosine receptors bound to adenosine and NECA [16], or by using fragments of antibodies to stabilize the agonist-bound state of the b2AR [17, 18]. These structures confirmed previous hypotheses [19,20,21,22] that the agonistbound active-state binding site is contracted by 1–2 Arelative to that bound to structurally related inverse agonists. The major conformational changes, occur on the intracellular side where transmembrane helices 5 and 6 (TM5 and 6) are extended and move outwards to allow binding of the G-protein

Objectives

Results

Conclusion