title: Interactions of brain muscarinic acetylcholine receptors with plant lectins.
abstract: We previously reported that muscarinic acetylcholine receptors (mAChRs) from porcine brains are glycoproteins. When porcine brain membranes were solubilized with digitonin or 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS), approximately 20% of the receptors were solubilized, most (90% or more) of which bound to Sepharose 4B conjugated with wheat germ agglutinin (WGA). In contrast, when membranes were solubilized with Lubrol PX, a much larger fraction (approximately 60%) of the receptors were solubilized. However, about a third of this solubilized receptor population remained unbound to WGA-Sepharose even in the presence of an excess amount of the lectin-Sepharose. These results suggested a structural heterogeneity of the mAChR in terms of its carbohydrate moiety. The effects of lectins on the ligand binding properties of mAChRs were also studied. WGA or concanavalin A (ConA) was found to cause a 2- to 3-fold increase in the affinity of membrane-bound receptors to an antagonist [3H]quinuclidinyl benzylate [( 3H]QNB) without affecting the maximum number of sites, whereas the lectins had no significant effects on the binding of the agonist [3H]cis-methyldioxolane. When the membranes were dissolved with detergents, lectin did not increase the [3H]QNB affinity: These lectins caused an approximately 2 fold decrease in the affinity of digitonin-solubilized receptors for [3H]QNB. Thus the lectins exert differential effects on agonist and antagonist binding to the brain membrane mAChRs, most likely by modulating some intermolecular interactions.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D037102:Lectins / Q000378:metabolism / Q000494:pharmacology*; D037121:Plant Lectins; D010944:Plants; D011485:Protein Binding; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D013552:Swine; D013574:Synaptosomes / Q000378:metabolism
chemical_list: D037102:Lectins; D037121:Plant Lectins; D011976:Receptors, Muscarinic; D011813:Quinuclidinyl Benzilate