RT Journal Article SR Electronic T1 Probing the Role of a Conserved M1 Proline Residue in 5-Hydroxytryptamine3 Receptor Gating JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 1114 OP 1122 VO 57 IS 6 A1 Hong Dang A1 Pamela M. England A1 S. Sarah Farivar A1 Dennis A. Dougherty A1 Henry A. Lester YR 2000 UL http://molpharm.aspetjournals.org/content/57/6/1114.abstract AB A conserved proline residue is found in the first transmembrane domain (M1) of every subunit in the ligand-gated ion channel superfamily. The position of this proline between the N-terminal extracellular agonist binding and the second transmembrane (M2) channel lining domains in the primary sequence suggests its possible involvement in the gating of the receptor. Replacing this proline with alanine, glycine, or leucine in the 5-hydroxytryptamine (5-HT)3A homomeric receptors expressed in Xenopus laevis oocytes resulted in the absence of 5-HT-induced whole-cell currents, although there were normal levels of specific surface [3H]granisetron ([3H]BRL-43694) binding sites. To determine what properties of the conserved proline are critical for the function of the channel, two imino acids and an α-hydroxy acid were incorporated at the proline position using the nonsense suppression method.trans-3-Methyl-proline, pipecolic acid, and leucic acid were able to replace the conserved proline to produce active channels with EC50 values similar to that for the wild-type receptor. These trends are preserved in the heteromeric receptors consisting of 5-HT3A and 5-HT3B subunits in oocytes. The prominent common feature among these residues and proline is the lack of hydrogen bond donor activity, potentially resulting in a flexible secondary structure in the M1 region. Thus, lack of hydrogen bond donor activity may be a key element in channel gating and may explain the high degree of conservation of this M1 proline. The American Society for Pharmacology and Experimental Therapeutics