A novel a-conotoxin, PeIA, cloned from Conus pergrandis discriminates between rat a9a10 and a7 nicotinic cholinergic receptors

MCINTOSH M; PLAZAS PV; WATKINS M; GOMEZ-CASATI M; OLIVERA BM; ELGOYHEN AB

J Biological Chemistry

Año: 2005 vol. 280 p. 30107 - 30112

The a9a10 receptor is a distant member of the family of nicotinic acetylcholine receptors (nAChRs). The four transmembrane (TM) domains of the nAChRs are likely to be involved in the conformational changes associated with gating. However, the lining of the pore, the gate, the size- and charge-selectivity filters are basically contributed by residues of TM2. We have performed a systematic mutagenesis of three hydrophobic rings within TM2 (outer 17’, 13’ and equatorial 9’) proposed to face the lumen of the channel, to a hydrophilic residue. We have compared the degree of the phenotypes of mutant receptors and provide functional evidence suggesting that the free energy of interactions of residues at the centrally located positions 9’ and 13’ of TM2 are major contributors to channel gating, in the case of the a9a10 nAChR. Moreover, 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’ are key ones in creating an energetic barrier to ion permeation. In spite of the fact that the roles of the TM2 residues are mostly conserved in the distant a9a10 member of the nAChR family, we provide evidence suggesting that 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.