Key roles of hydrophobic rings of TM2 in gating of the alpha9alpha10 nicotinic acetylcholine receptor

PAOLA V. PLAZAS; MARÍA J. DE ROSA; MARIA E GOMEZ CASATI; MIGUEL VERBITSKY; NOELIA WEISSTAUB; ELEONORA KATZ; CECILIA BOUZAT; A BELEN ELGOYHEN.

BRITISH JOURNAL OF PHARMACOLOGY

Año: 2005 vol. 145 p. 963 - 974

0007-1188

1. We have performed a systematic mutagenesis of three hydrophobic rings (17’, 13’ and 9’) within transmembrane region (TM) 2 of the a9a10 nicotinic cholinergic receptor (nAChR), to a hydrophilic (threonine) residue and compared the properties of mutant receptors reconstituted in Xenopus laevis oocytes. 2. Phenotypic changes in a9a10 mutant receptors were evidenced by a decrease in the desensitization rate, an increase in both the EC50 for ACh as well as the efficacy of partial agonists, and the reduction of the allosteric modulation by extracellular Ca2+. 3. Mutated receptors exhibited spontaneous openings and at the single channel level an increased apparent mean open time with no major changes in channel conductance, thus suggesting an increase in gating of the channel as the underlying mechanism. 4. Overall the degree of the phenotypes of mutant receptors where more overt in the case of the centrally located V13’T mutant. 5. Based on the atomic model of the pore of the electric organ of the Torpedo ray, we can propose that the interactions of side chains at position 13’ and 9’ are key ones in creating an energetic barrier to ion permeation. 6.         In spite of the fact that the roles of the TM2 residues are mostly conserved in the distant a9a10 member of the nAChR family, their mechanistic contributions to channel gating show significant differences when compared to other nAChRs. These differences might be originated from slight differential intramolecular rearrangements during gating for the different receptors and might lead each nAChR to be in tune with their physiological roles.