QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: mol.108.050963v1 75/2/331    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lebon, G. Articles by Hulme, E. C. Search for Related Content PubMed PubMed Citation Articles by Lebon, G. Articles by Hulme, E. C.

Mutagenic Mapping Suggests a Novel Binding Mode for Selective Agonists of M₁ Muscarinic Acetylcholine Receptors

Division of Physical Biochemistry, MRC National Institute for Medical Research, Mill Hill, London, United Kingdom (E.C.H., G.L.); and GlaxoSmithKline, New Frontiers Science Park, Harlow, Essex, United Kingdom (C.J.L., B.G.T.)

Point mutations and molecular modeling have been used to study the activation of the M₁ muscarinic acetylcholine receptor (mAChR) by the functionally selective agonists 4-n-butyl-1-[4-(2-methylphenyl)-4-oxo-1-butyl]-piperidine (AC-42), and 1-[3-(4-butyl-1-piperidinyl)propyl]-3,4-dihydro-2(1H)-quinolinone (77-LH-28-1), comparing them with N-desmethylclozapine (NDMC) and acetylcholine (ACh). Unlike NDMC and ACh, the activities of AC-42 and 77-LH-28-1 were undiminished by mutations of Tyr404 and Cys407 (transmembrane helix 7), although they were reduced by mutations of Tyr408. Signaling by AC-42, 77-LH-28-1, and NDMC was reduced by L102A and abolished by D105E, suggesting that all three may interact with transmembrane helix 3 at or near the binding site Asp105 to activate the M₁ mAChR. In striking contrast to NDMC and ACh, the affinities of AC-42 and 77-LH-28-1 were increased 100-fold by W101A, and their signaling activities were abolished by Y82A. Tyr82 and Leu102 contact the indole ring of Trp101 in a structural model of the M₁ mAChR. We suggest the hypothesis that the side chain of Trp101 undergoes conformational isomerization, opening a novel binding site for the aromatic side chain of the AC-42 analogs. This may allow the positively charged piperidine nitrogen of the ligands to access the neighboring Asp105 carboxylate to activate signaling following a vector within the binding site that is distinct from that of acetylcholine. NDMC does not seem to use this mechanism. Subtype-specific differences in the free energy of rotation of the side chain and indole ring of Trp101 might underlie the M₁ selectivity of the AC-42 analogs. Tryptophan conformational isomerization may open up new avenues in selective muscarinic receptor drug design.

Received for publication July 31, 2008.

Accepted for publication November 11, 2008.

Address correspondence to: Dr. E. C. Hulme, Division of Physical Biochemistry, MRC National Institute for Medical Research, Mill Hill, London NW7 1AA, UK. E-mail: ehulme{at}nimr.mrc.ac.uk

This article has been cited by other articles:

				C. Valant, P. M. Sexton, and A. Christopoulos Orthosteric/Allosteric Bitopic Ligands: Going Hybrid at GPCRs Mol. Interv., June 1, 2009; 9(3): 125 - 135. [Abstract] [Full Text] [PDF]