scholarly journals Understanding G Protein Selectivity of Muscarinic Acetylcholine Receptors Using Computational Methods

2019 ◽  
Vol 20 (21) ◽  
pp. 5290
Author(s):  
Luis Santiago ◽  
Ravinder Abrol
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Protein Interactions ◽  
Intracellular Signaling ◽  
Acetylcholine Receptors ◽  
Experimental Studies ◽  
Muscarinic Acetylcholine Receptors ◽  
Structural Basis ◽  
Receptor Subtypes ◽  
Muscarinic Acetylcholine

The neurotransmitter molecule acetylcholine is capable of activating five muscarinic acetylcholine receptors, M1 through M5, which belong to the superfamily of G-protein-coupled receptors (GPCRs). These five receptors share high sequence and structure homology; however, the M1, M3, and M5 receptor subtypes signal preferentially through the Gαq/11 subset of G proteins, whereas the M2 and M4 receptor subtypes signal through the Gαi/o subset of G proteins, resulting in very different intracellular signaling cascades and physiological effects. The structural basis for this innate ability of the M1/M3/M5 set of receptors and the highly homologous M2/M4 set of receptors to couple to different G proteins is poorly understood. In this study, we used molecular dynamics (MD) simulations coupled with thermodynamic analyses of M1 and M2 receptors coupled to both Gαi and Gαq to understand the structural basis of the M1 receptor’s preference for the Gαq protein and the M2 receptor’s preference for the Gαi protein. The MD studies showed that the M1 and M2 receptors can couple to both Gα proteins such that the M1 receptor engages with the two Gα proteins in slightly different orientations and the M2 receptor engages with the two Gα proteins in the same orientation. Thermodynamic studies of the free energy of binding of the receptors to the Gα proteins showed that the M1 and M2 receptors bind more strongly to their cognate Gα proteins compared to their non-cognate ones, which is in line with previous experimental studies on the M3 receptor. A detailed analysis of receptor–G protein interactions showed some cognate-complex-specific interactions for the M2:Gαi complex; however, G protein selectivity determinants are spread over a large overlapping subset of residues. Conserved interaction between transmembrane helices 5 and 6 far away from the G-protein-binding receptor interface was found only in the two cognate complexes and not in the non-cognate complexes. An analysis of residues implicated previously in G protein selectivity, in light of the cognate and non-cognate structures, shaded a more nuanced role of those residues in affecting G protein selectivity. The simulation of both cognate and non-cognate receptor–G protein complexes fills a structural gap due to difficulties in determining non-cognate complex structures and provides an enhanced framework to probe the mechanisms of G protein selectivity exhibited by most GPCRs.

scholarly journals Structures of the M1 and M2 muscarinic acetylcholine receptor/G-protein complexes

Science ◽  
2019 ◽  
Vol 364 (6440) ◽  
pp. 552-557 ◽  
Author(s):  
Shoji Maeda ◽  
Qianhui Qu ◽  
Michael J. Robertson ◽  
Georgios Skiniotis ◽  
Brian K. Kobilka
Keyword(s):  
G Protein ◽  
Acetylcholine Receptors ◽  
Protein Complexes ◽  
Transmembrane Helix ◽  
Muscarinic Acetylcholine Receptor ◽  
Muscarinic Acetylcholine Receptors ◽  
Receptor Subtypes ◽  
Muscarinic Acetylcholine ◽  
High Degree ◽  
Distinct Features

Muscarinic acetylcholine receptors are G protein–coupled receptors that respond to acetylcholine and play important signaling roles in the nervous system. There are five muscarinic receptor subtypes (M1R to M5R), which, despite sharing a high degree of sequence identity in the transmembrane region, couple to different heterotrimeric GTP-binding proteins (G proteins) to transmit signals. M1R, M3R, and M5R couple to the Gq/11 family, whereas M2R and M4R couple to the Gi/o family. Here, we present and compare the cryo–electron microscopy structures of M1R in complex with G11 and M2R in complex with GoA. The M1R-G11 complex exhibits distinct features, including an extended transmembrane helix 5 and carboxyl-terminal receptor tail that interacts with G protein. Detailed analysis of these structures provides a framework for understanding the molecular determinants of G-protein coupling selectivity.

scholarly journals Role of M1, M3, and M5 muscarinic acetylcholine receptors in cholinergic dilation of small arteries studied with gene-targeted mice

2011 ◽  
Vol 300 (5) ◽  
pp. H1602-H1608 ◽  
Author(s):  
Adrian Gericke ◽  
Jan J. Sniatecki ◽  
Veronique G. A. Mayer ◽  
Evgeny Goloborodko ◽  
Andreas Patzak ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscarinic Receptor ◽  
Acetylcholine Receptors ◽  
Muscarinic Acetylcholine Receptors ◽  
Receptor Subtypes ◽  
Wild Type ◽  
Luminal Diameter ◽  
Small Arteries ◽  
Muscarinic Acetylcholine

Acetylcholine regulates perfusion of numerous organs via changes in local blood flow involving muscarinic receptor-induced release of vasorelaxing agents from the endothelium. The purpose of the present study was to determine the role of M1, M3, and M5 muscarinic acetylcholine receptors in vasodilation of small arteries using gene-targeted mice deficient in either of the three receptor subtypes (M1R−/−, M3R−/−, or M5R−/− mice, respectively). Muscarinic receptor gene expression was determined in murine cutaneous, skeletal muscle, and renal interlobar arteries using real-time PCR. Moreover, respective arteries from M1R−/−, M3R−/−, M5R−/−, and wild-type mice were isolated, cannulated with micropipettes, and pressurized. Luminal diameter was measured using video microscopy. mRNA for all five muscarinic receptor subtypes was detected in all three vascular preparations from wild-type mice. However, M3 receptor mRNA was found to be most abundant. Acetylcholine produced dose-dependent dilation in all three vascular preparations from M1R−/−, M5R−/−, and wild-type mice. In contrast, cholinergic dilation was virtually abolished in arteries from M3R−/− mice. Deletion of either M1, M3, or M5 receptor genes did not affect responses to nonmuscarinic vasodilators, such as substance P and nitroprusside. These findings provide the first direct evidence that M3 receptors mediate cholinergic vasodilation in cutaneous, skeletal muscle, and renal interlobar arteries. In contrast, neither M1 nor M5 receptors appear to be involved in cholinergic responses of the three vascular preparations tested.

M1 and M2 Muscarinic Acetylcholine Receptor Subtypes Mediate Ca2+ Channel Current Inhibition in Rat Sympathetic Stellate Ganglion Neurons

2006 ◽  
Vol 96 (5) ◽  
pp. 2479-2487 ◽  
Author(s):  
Qing Yang ◽  
Andrew D. Sumner ◽  
Henry L. Puhl ◽  
Victor Ruiz-Velasco
Keyword(s):  
Acetylcholine Receptors ◽  
Stellate Ganglion ◽  
Muscarinic Acetylcholine Receptor ◽  
Muscarinic Acetylcholine Receptors ◽  
Receptor Subtypes ◽  
Muscarinic Acetylcholine ◽  
Peripheral Neurons ◽  
Voltage Dependent ◽  
Ganglion Neurons ◽  
Channel Currents

Muscarinic acetylcholine receptors (mAChRs) are known to mediate the acetylcholine inhibition of Ca2+ channels in central and peripheral neurons. Stellate ganglion (SG) neurons provide the main sympathetic input to the heart and contribute to the regulation of heart rate and myocardial contractility. Little information is available regarding mAChR regulation of Ca2+ channels in SG neurons. The purpose of this study was to identify the mAChR subtypes that modulate Ca2+ channel currents in rat SG neurons innervating heart muscle. Accordingly, the modulation of Ca2+ channel currents by the muscarinic cholinergic agonist, oxotremorine-methiodide (Oxo-M), and mAChR blockers was examined. Oxo-M–mediated mAChR stimulation led to inhibition of Ca2+ currents through voltage-dependent (VD) and voltage-independent (VI) pathways. Pre-exposure of SG neurons to the M1 receptor blocker, M1-toxin, resulted in VD inhibition of Ca2+ currents after Oxo-M application. On the other hand, VI modulation of Ca2+ currents was observed after pretreatment of cells with methoctramine (M2 mAChR blocker). The Oxo-M–mediated inhibition was nearly eliminated in the presence of both M1 and M2 mAChR blockers but was unaltered when SG neurons were exposed to the M4 mAChR toxin, M4-toxin. Finally, the results from single-cell RT-PCR and immunofluorescence assays indicated that M1 and M2 receptors are expressed and located on the surface of SG neurons. Overall, the results indicate that SG neurons that innervate cardiac muscle express M1 and M2 mAChR, and activation of these receptors leads to inhibition of Ca2+ channel currents through VI and VD pathways, respectively.

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