A Trk/HKT-type K+ transporter from Trypanosoma brucei

Eukaryot Cell. 2010 Apr;9(4):539-46. doi: 10.1128/EC.00314-09. Epub 2010 Feb 26.


The molecular mechanisms of K(+) homeostasis are only poorly understood for protozoan parasites. Trypanosoma brucei subsp. parasites, the causative agents of human sleeping sickness and nagana, are strictly extracellular and need to actively concentrate K(+) from their hosts' body fluids. The T. brucei genome contains two putative K(+) channel genes, yet the trypanosomes are insensitive to K(+) antagonists and K(+) channel-blocking agents, and they do not spontaneously depolarize in response to high extracellular K(+) concentrations. However, the trypanosomes are extremely sensitive to K(+) ionophores such as valinomycin. Surprisingly, T. brucei possesses a member of the Trk/HKT superfamily of monovalent cation permeases which so far had only been known from bacteria, archaea, fungi, and plants. The protein was named TbHKT1 and functions as a Na(+)-independent K(+) transporter when expressed in Escherichia coli, Saccharomyces cerevisiae, or Xenopus laevis oocytes. In trypanosomes, TbHKT1 is expressed in both the mammalian bloodstream stage and the Tsetse fly midgut stage; however, RNA interference (RNAi)-mediated silencing of TbHKT1 expression did not produce a growth phenotype in either stage. The presence of HKT genes in trypanosomatids adds a further piece to the enigmatic phylogeny of the Trk/HKT superfamily of K(+) transporters. Parsimonial analysis suggests that the transporters were present in the first eukaryotes but subsequently lost in several of the major eukaryotic lineages, in at least four independent events.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cation Transport Proteins / classification
  • Cation Transport Proteins / genetics
  • Cation Transport Proteins / metabolism*
  • Cell Line
  • Humans
  • Molecular Sequence Data
  • Oocytes / cytology
  • Oocytes / physiology
  • Patch-Clamp Techniques
  • Phenotype
  • Phylogeny
  • Potassium / metabolism*
  • Protozoan Proteins / classification
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism*
  • RNA Interference
  • Trypanosoma brucei brucei / cytology
  • Trypanosoma brucei brucei / genetics
  • Trypanosoma brucei brucei / metabolism*
  • Tsetse Flies / metabolism
  • Tsetse Flies / parasitology
  • Xenopus laevis


  • Cation Transport Proteins
  • HKT1 protein, Trypanosoma brucei
  • Protozoan Proteins
  • Potassium