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Role of membrane cholesterol in differential sensitivity of muscarinic receptor subtypes to persistently bound xanomeline

Role of membrane cholesterol in differential sensitivity of muscarinic receptor subtypes to persistently bound xanomeline

Our new publication in journal Neuropharmacology in which we demonstrate that membrane cholesterol plays an important and subtype-specific role in activation of muscarinic acetylcholine receptors. To our knowledge, this is the first demonstration of pharmacological selectivity due to differences in receptor-membrane interactions at any GPCR. The possibility to achieve pharmacological selectivity based on receptor-membrane interactions changes our view on the molecular basis of pharmacological selectivity and opens new ways for the development of a novel pharmaceutics.

Xanomeline (3-(Hexyloxy)-4-(1-methyl-1,2,5,6-tetrahydropyridin-3-yl)-1,2,5-thiadiazole) is a muscarinic agonist that is considered to be functionally selective for the M1/M4 receptor subtypes. Part of xanomeline binding is resistant to washing. Wash-resistant xanomeline activates muscarinic receptors persistently, except for the M5 subtype. Mutation of leucine 6.46 to isoleucine at M1 or M4 receptors abolished persistent activation by wash-resistant xanomeline. Reciprocal mutation of isoleucine 6.46 to leucine at the M5 receptor made it sensitive to activation by wash-resistant xanomeline. Lowering of membrane cholesterol made M1 and M4 mutants and M5 wild type receptors sensitive to activation by wash-resistant xanomeline. Molecular docking revealed a cholesterol binding site in the groove between transmembrane helices 6 and 7. Molecular dynamics showed that interaction of cholesterol with this binding site attenuates receptor activation. We hypothesize that differences in cholesterol binding to this site between muscarinic receptor subtypes may constitute the basis for xanomeline apparent functional selectivity and may have notable therapeutic implications. Differences in receptor-membrane interactions, rather than in agonist-receptor interactions, represent a novel possibility to achieve pharmacological selectivity. Our findings may be applicable to other G protein coupled receptors.


 

Cholesterol binding to the intracellular half of TM6 of wt (left) and L376I mutant (right) M1 receptor based on crystal structure 5CXV (Thal et al., 2016) is shown. Orientation, extracellular side up, TM6 front. Colours: magenta, surface of TM5, TM6 and TM7, yellow, surface of R365, L376 and I376; cyan, carbon; white, hydrogen; red, oxygen.


https://www.ncbi.nlm.nih.gov/pubmed/29407765