Artículos de revistas
Mechanistic contributions of residues in the M1 transmembrane domain of the nicotinic receptor to channel gating
Date
2004-01Registration in:
Spitzmaul, Guillermo Federico; Corradi, Jeremias; Bouzat, Cecilia Beatriz; Mechanistic contributions of residues in the M1 transmembrane domain of the nicotinic receptor to channel gating; Taylor & Francis Ltd; Molecular Membrane Biology; 21; 1; 1-2004; 39-50
0968-7688
CONICET Digital
CONICET
Author
Spitzmaul, Guillermo Federico
Corradi, Jeremias
Bouzat, Cecilia Beatriz
Abstract
The nicotinic receptor (AChR) is a pentamer of homologous subunits with an α2βεδ composition in adult muscle. Each subunit contains four transmembrane domains (M1-M4). Position 15′ of the M1 domain is phenylalanine in α subunits while it is isoleucine in non-α subunits. Given this peculiar conservation pattern, we studied its contribution to muscle AChR activation by combining mutagenesis with single-channel kinetic analysis. AChRs containing the mutant α subunit (αF15′I) as well as those containing the reverse mutations in the non-α subunits (βI15′F, δI15′F, and εI15′F) show prolonged lifetimes of the diliganded open channel resulting from a slower closing rate with respect to wild-type AChRs. The kinetic changes are not equivalent among subunits, the β subunit, being the one that produces the most significant stabilization of the open state. Kinetic analysis of βI15′F AChR channels activated by the low-efficacious agonist choline revealed a 10-fold decrease in the closing rate, a 2.5-fold increase in the opening rate, a 28-fold increase in the gating equilibrium constant of the diliganded receptor, and a significant increased opening in the absence of agonist. Mutations at βI15′ showed that the structural bases of its contribution to gating is complex. Rate-equilibrium linear free-energy relationships suggest an ∼70% closed-state-like environment for the β15′ position at the transition state of gating. The overall results identify position 15′ as a subunit-selective determinant of channel gating and add new experimental evidence that gives support to the involvement of the M1 domain in the operation of the channel gating apparatus.