The Journal of Membrane Biology

, Volume 214, Issue 3, pp 131–138

The Polarity of Lipid-Exposed Residues Contributes to the Functional Differences between Torpedo and Muscle-Type Nicotinic Receptors

  • Gisila R. Guzmán
  • Alejandro Ortiz-Acevedo
  • Ariamsi Ricardo
  • Legier V. Rojas
  • José A. Lasalde-Dominicci
Article

DOI: 10.1007/s00232-006-0051-0

Cite this article as:
Guzmán, G.R., Ortiz-Acevedo, A., Ricardo, A. et al. J Membrane Biol (2006) 214: 131. doi:10.1007/s00232-006-0051-0

Abstract

A comparison between the Torpedo and muscle-type acetylcholine receptors (AChRs) reveals differences in several lipid-exposed amino acids, particularly in the polarity of those residues. The goal of this study was to characterize the role of eight lipid-exposed residues in the functional differences between the Torpedo and muscle-type AChRs. To this end, residues αS287, αC412, βY441, γM299, γS460, δM293, δS297 and δN305 in the Torpedo AChR were replaced with those found in the muscle-type receptor. Mutant receptor expression was measured in Xenopus oocytes using [125I]-α-bungarotoxin, and AChR ion channel function was evaluated using the two-electrode voltage clamp. Eight mutant combinations resulted in an increase (1.5- to 5.2-fold) in AChR expression. Four mutant combinations produced a significant 46% decrease in the ACh 50% inhibitory concentration (EC50), while three mutant combinations resulted in 1.7- to 2-fold increases in ACh EC50. Finally, seven mutant combinations resulted in a decrease in normalized, ACh-induced currents. Our results suggest that these residues, although remote from the ion channel pore, (1) contribute to ion channel gating, (2) may affect trafficking of AChR into specialized membrane domains and (3) account for the functional differences between Torpedo and muscle-type AChR. These findings emphasize the importance of the lipid-protein interface in the functional differences between the Torpedo and muscle-type AChRs.

Keywords

Acetylcholine receptor Site-directed mutagenesis Xenopus oocyte Lipid-exposed residue Torpedo californica Muscle-type receptor 

Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • Gisila R. Guzmán
    • 1
  • Alejandro Ortiz-Acevedo
    • 1
  • Ariamsi Ricardo
    • 1
  • Legier V. Rojas
    • 2
  • José A. Lasalde-Dominicci
    • 1
  1. 1.Department of BiologyUniversity of Puerto RicoSan Juan
  2. 2.Department of PhysiologySchool of Medicine, Universidad Central del CaribeBayamón