title: Toward activated homology models of the human M1 muscarinic acetylcholine receptor.
abstract: Structure-based virtual screening offers a good opportunity for the discovery of selective M1 muscarinic acetylcholine receptor (mAChR) agonists for the treatment of Alzheimer's disease. However, no 3-D structure of an M1 mAChR is yet available and the homology models that have been previously reported are only able to identify antagonists in virtual screening experiments. In this study, we generated a homology model of the human M1 mAChR, based on the crystal structure of an M3 mAChR as the template. This initial model was modified, using the agonist-bound crystal structure of a β2-adrenergic receptor as a guide, to give two possible activated structures. The T192 side chain was adjusted in both structures and one of the structures also had the whole of transmembrane (TM) 5 rotated and tilted toward the inner channel of the transmembrane region. The binding sites of all three structures were then refined by induced-fit docking (IFD) with acetylcholine. Virtual screening experiments showed that all three refined models could efficiently differentiate agonists from decoy molecules, with the TM5-modified models also giving good agonist/antagonist selectivity. The whole range of agonists and antagonists was observed to bind within the orthosteric site of the structure obtained by IFD refinement alone, implying that it has inactive state character. In contrast, the two TM5-modified structures were unable to accommodate the antagonists, supporting the proposition that they possess activated state character.
authors.affiliation: Department of Pharmacy, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia.
authors.forename: Sek Peng
authors.initials: SP
authors.lastname: Chin
authors.affiliation: Department of Pharmacy, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia. Electronic address: buckle@um.edu.my.
authors.forename: Michael J C
authors.initials: MJ
authors.lastname: Buckle
authors.affiliation: Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville Campus), 381 Royal Parade, Parkville, Victoria 3052, Australia.
authors.forename: David K
authors.initials: DK
authors.lastname: Chalmers
authors.affiliation: Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville Campus), 381 Royal Parade, Parkville, Victoria 3052, Australia.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Yuriev
authors.affiliation: The School of Pharmacy, University of Nottingham Malaysia Campus, Jalan Broga, 43500 Semenyih, Selangor, Malaysia. Electronic address: stephen.doughty@nottingham.edu.my.
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Doughty
mesh_terms: D001665:Binding Sites; D006801:Humans; D011485:Protein Binding; D017433:Protein Structure, Secondary; D043643:Receptor, Muscarinic M1 / Q000737:chemistry* / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry / Q000378:metabolism
chemical_list: D043643:Receptor, Muscarinic M1; D043562:Receptors, G-Protein-Coupled
keywords: Activated structure; Docking; G protein-coupled receptor; Homology modeling; Virtual screening