title: Involvement of multiple sulfhydryl groups in melatonin signal transduction in chick brain.
abstract: To gain insight into the molecular mechanism underlying melatonin binding and signal transduction in the chick brain, we have investigated the role of -SH groups, using a sulfhydryl alkylating reagent N-ethylmaleimide (NEM). At least two -SH groups are involved in the formation of the receptor-G protein complex: one is sensitive to and the other relatively insensitive to NEM. Alkylation of the sensitive group selectively abolishes high affinity binding of 2-[125I]iodomelatonin ([125I]MEL), similar to the effect induced by GTP, thus leading to a complete loss of sensitivity to nucleotides. Modification of both groups causes a marked reduction in binding capacity. Agonists with high affinity, but not other compounds with low affinity for the melatonin receptor, protect against alkylation by NEM. GTP gamma s does not significantly alter the reactivity of -SH groups towards NEM, but agonist-protected receptors remain sensitive to this nucleotide. Moreover, NEM pretreatment blocks the inhibitory effect of melatonin on forskolin-stimulated adenylate cyclase activity in chick brain. These data suggest that the -SH group modulating agonist affinity may lie within the coupling domain between the receptor and G protein but outside of the GTP binding site. In addition, sulfhydryl groups are essential for melatonin binding and signal transduction in chick brain.
authors.affiliation: Department of Biomedical Sciences, McMaster University, Hamilton, Ont., Canada.
authors.forename: S W
authors.initials: SW
authors.lastname: Ying
authors.forename: L
authors.initials: L
authors.lastname: Niles
authors.forename: D
authors.initials: D
authors.lastname: Pickering
authors.forename: M
authors.initials: M
authors.lastname: Ye
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000478:Alkylation; D000704:Analysis of Variance; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002645:Chickens; D005033:Ethylmaleimide / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000494:pharmacology; D008297:Male; D008550:Melatonin / Q000378:metabolism* / Q000494:pharmacology; D044094:Receptors, Melatonin; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013574:Synaptosomes / Q000378:metabolism*
chemical_list: D044094:Receptors, Melatonin; D017981:Receptors, Neurotransmitter; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D008550:Melatonin; D005033:Ethylmaleimide