An interaction involving an arginine residue in the cytoplasmic domain of the 5-HT3A receptor contributes to receptor desensitization mechanism.
A large cytoplasmic domain accounts for approximately one-third of the entire protein of one superfamily of ligand-gated membrane ion channels, which includes nicotinic acetylcholine (nACh), gamma-aminobutyric acid type A (GABA(A)), serotonin type 3 (5-HT3), and glycine receptors. Desensitization is one functional feature shared by these receptors. Because most molecular studies of receptor desensitization have focused on the agonist binding and channel pore domains, relatively little is known about the role of the large cytoplasmic domain (LCD) in this process. To address this issue, we sequentially deleted segments of the LCD of the 5-HT3A receptor and examined the function of the mutant receptors. Deletion of a small segment that contains three amino acid residues (425-427) significantly slowed the desensitization kinetics of the 5-HT3A receptor. Both deletion and point mutation of arginine 427 altered desensitization kinetics in a manner similar to that of the (425-427) deletion without significantly changing the apparent agonist affinity. The extent of receptor desensitization was positively correlated with the polarity of the amino acid residue at 427: the desensitization accelerates with increasing polarity. Whereas the R427L mutation produced the slowest desensitization, it did not significantly alter single channel conductance of 5-HT3A receptor. Thus, the arginine 427 residue in the LCD contributes to 5-HT3A receptor desensitization, possibly through forming an electrostatic interaction with its neighboring residues. Because the polarity of the amino acid residue at 427 is highly conserved, such a desensitization mechanism may occur in other members of the Cys-loop family of ligand-gated ion channels.
Hu
Xiang-Qun
XQ
Laboratory for Integrative Neuroscience, National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland 20892-8115.
Sun
Hui
H
Laboratory for Integrative Neuroscience, National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland 20892-8115.
Peoples
Robert W
RW
Department of Biomedical Sciences, College of Health Sciences, Marquette University, Milwaukee, Wisconsin 53201-1881.
Hong
Ren
R
Department of Biomedical Sciences, College of Health Sciences, Marquette University, Milwaukee, Wisconsin 53201-1881.
Zhang
Li
L
Laboratory for Integrative Neuroscience, National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland 20892-8115. Electronic address: lzhang@mail.nih.gov.
D000596:Amino Acids; D000818:Animals; D001120:Arginine; D003593:Cytoplasm; D004594:Electrophysiology; D015640:Ion Channel Gating; D007700:Kinetics; D051379:Mice; D009154:Mutation; D017434:Protein Structure, Tertiary; D044406:Receptors, Serotonin, 5-HT3 / Q000235:genetics / Q000502:physiology*; D055672:Static Electricity; D014982:Xenopus laevis
D000596:Amino Acids; D044406:Receptors, Serotonin, 5-HT3; D001120:Arginine