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The unanticipated complexity of the selectivity-filter glutamates of nicotinic receptors

Nature Chemical Biology volume 8, pages 975–981 (2012)Cite this article

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Abstract

In ion channels, 'rings' of ionized side chains that decorate the walls of the permeation pathway often lower the energetic barrier to ion conduction. Using single-channel electrophysiological recordings, we studied the poorly understood ring of four glutamates (and one glutamine) that dominates this catalytic effect in the muscle nicotinic acetylcholine receptor ('the intermediate ring of charge'). We show that all four wild-type glutamate side chains are deprotonated in the range of 6.0–9.0 pH, that only two of them contribute to the size of the single-channel current, that these side chains must be able to adopt alternate conformations that either allow or prevent their negative charges from increasing the rate of cation conduction and that the location of these glutamate side chains squarely at one of the ends of the transmembrane pore is critical for their largely unshifted pKa values and for the unanticipated impact of their conformational flexibility on cation permeation.

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Figure 1: The intermediate ring of glutamates.
Figure 2: Mutations reveal a complex conductance behavior.
Figure 3: The pH dependence of intermediate-ring mutants is weak.
Figure 4: The conformational dynamics are sensitive to the local electrostatics.
Figure 5: Moving the intermediate ring of glutamates into the pore.

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Acknowledgements

We thank S. Sine (Mayo Clinic College of Medicine, Rochester, MN, USA) for wild-type muscle AChR cDNA, M. Slaughter (University at Buffalo School of Medicine, Buffalo, NY, USA) for wild-type α1 GlyR cDNA, and A. Holmstrom, M. Pasquini, J. Pizarek and M. Rigby for technical assistance. This work was supported by a grant from the US National Institutes of Health (R01-NS042169 to C.G.).

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Authors and Affiliations

  1. Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA

    Gisela D Cymes & Claudio Grosman

  2. Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA

    Claudio Grosman

  3. Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA

    Claudio Grosman

Authors
  1. Gisela D Cymes
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Contributions

G.D.C. and C.G. designed experiments, analyzed data and wrote the manuscript. G.D.C. performed experiments.

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Correspondence to Claudio Grosman.

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Cymes, G., Grosman, C. The unanticipated complexity of the selectivity-filter glutamates of nicotinic receptors. Nat Chem Biol 8, 975–981 (2012). https://doi.org/10.1038/nchembio.1092

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