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Pflugers Arch. 2015 Dec;467(12):2447-60. doi: 10.1007/s00424-015-1712-6. Epub 2015 Jun 24.

A structural model for facultative anion channels in an oligomeric membrane protein: the yeast TRK (K(+)) system.

Author information

  • 1Departamento de Bioquimica, Facultad de Medicina, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Coyoacan, 04510, Mexico, D.F., Mexico. pardov@laguna.fmedic.unam.mx.
  • 2Departamento de Bioquimica, Facultad de Medicina, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Coyoacan, 04510, Mexico, D.F., Mexico. martin@bq.unam.mx.
  • 3Department of Genetics, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06520, USA. kenneth.allen@yale.edu.
  • 4Department of Microbiology, Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, 1-1-1 Tsushima-Naka, Kita-ku, Okayama, 700-8530, Japan. tkuroda@cc.okayama-u.ac.jp.
  • 5Department of Cellular and Molecular Physiology, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06520, USA. clifford.slayman@yale.edu.
  • 6Department of Cellular and Molecular Physiology, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06520, USA. alberto.rivetta@yale.edu.

Abstract

TRK transporters, a class of proteins which generally carry out the bulk of K(+) accumulation in plants, fungi, and bacteria, mediate ion currents driven by the large membrane voltages (-150 to -250 mV) common to non-animal cells. Bacterial TRK proteins resemble K(+) channels in their primary sequence, crystallize as membrane dimers having intramolecular K(+)-channel-like folding, and complex with a cytoplasmic collar formed of four RCK domains (Nature 471:336, 2011; Ibid 496:324, 2013). Fungal TRK proteins appear simpler in form than the bacterial members, but do possess two special features: a large built-in regulatory domain, and a highly conserved pair of transmembrane helices (TM7 and TM8, ahead of the C-terminus), which were postulated to facilitate intramembranal oligomerization (Biophys. J. 77:789, 1999; FEMS Yeast Res. 9:278, 2009). A surprising associated functional process in the fungal proteins which have been explored (Saccharomyces, Candida, and Neurospora) is facilitation of channel-like chloride efflux. That process is suppressed by osmoprotective agents, appears to involve hydrophobic gating, and strongly resembles conduction by Cys-loop ligand-gated anion channels. And it leads to a rather general hypothesis: that the thermodynamic tendency for hydrophobic or amphipathic transmembrane helices to self-organize into oligomers can create novel ionic pathways through biological membranes: fundamental hydrophobic nanopores, pathways of low selectivity governed by the chaotropic behavior of individual ionic species and under the strong influence of membrane voltage.

KEYWORDS:

Chaotropic anions; Compatible solutes; Ligand-gated channels; Microbial chloride efflux; TRK-potassium transporters

PMID:
26100673
DOI:
10.1007/s00424-015-1712-6
[PubMed - indexed for MEDLINE]
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