Analyses of gating thermodynamics and effects of deletions in the mechanosensitive channel TREK-1: comparisons with structural models

Channels (Austin). Jan-Feb 2011;5(1):34-42. doi: 10.4161/chan.5.1.13906. Epub 2011 Jan 1.

Abstract

TREK-1, a mechanosensitive K channel from the two-pore family (K(2)P), is involved in protective regulation of the resting potential in CNS neurons and other tissues. The structure of TREK-1 and the basis of its sensitivity to stretch and variety of lipid-soluble factors remain unknown. Using existing K channel structures as modeling templates, TREK-1 was envisioned as a two-fold symmetrical complex with the gate formed primarily by the centrally positioned TM2b helices of the second homologous repeat. Opening was modeled as a conical expansion of the barrel separating TM2b's accompanied by extension of TM2a helices with the cytoplasmic TM2a-TM1b connector. Seeking first experimental support to the models we have accomplished thermodynamic analysis of mouse TREK-1 gating and functional testing of several deletion mutants. The predicted increase of the channel in-plane area (ΔA) of ~5 nm(2) in models was supported by the experimental ΔA of ~4 nm(2) derived from the slope of open probability versus membrane tension in HEK-293T cells and their cytoskeleton-depleted blebs. In response to steps of suction, wild-type channel produced transient currents in cell-attached patches and mostly sustained currents upon patch excision. TREK-1 motifs not present in canonical K channels include divergent cytoplasmic N- and C-termini, and a characteristic 50-residue extracellular loop in the first homologous repeat. Deletion of the extracellular loop (Δ76-124) reduced the average current density in patches, increased spontaneous activity and generated a larger sub-population of high-conductance channels, while activation by tension augmented by arachidonic acid was fully retained. Further deletion of the C-terminal end (Δ76-124/Δ334-411) removed voltage dependency but otherwise produced no additional effect. In an attempt to generate a cysteine-free version of the channel, we mutated two remaining cysteines 159 and 219 in the transmembrane region. C219A did not compromise channel activity, whereas the C159A/S mutants were essentially inactive. Treatment with β-mercaptoethanol suggested that none of these cysteines form functionally-important disulfides.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Intramural

MeSH terms

  • Animals
  • Cysteine
  • HEK293 Cells
  • Humans
  • Ion Channel Gating*
  • Mechanotransduction, Cellular*
  • Membrane Potentials
  • Mercaptoethanol / pharmacology
  • Mice
  • Models, Molecular*
  • Mutagenesis, Site-Directed
  • Patch-Clamp Techniques
  • Potassium Channels, Tandem Pore Domain / chemistry
  • Potassium Channels, Tandem Pore Domain / drug effects
  • Potassium Channels, Tandem Pore Domain / genetics
  • Potassium Channels, Tandem Pore Domain / metabolism*
  • Pressure
  • Protein Conformation
  • Protein Structure, Tertiary
  • Sequence Deletion*
  • Structure-Activity Relationship
  • Thermodynamics*
  • Transfection

Substances

  • Potassium Channels, Tandem Pore Domain
  • potassium channel protein TREK-1
  • Mercaptoethanol
  • Cysteine