A Trk/HKT-type K+ transporter from Trypanosoma brucei.
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.
Mosimann
Marc
M
Institute of Cell Biology, University of Bern, Bern, Switzerland.
Goshima
Shinobu
S
Wenzler
Tanja
T
Lüscher
Alexandra
A
Uozumi
Nobuyuki
N
Mäser
Pascal
P
D000818:Animals; D027682:Cation Transport Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D008969:Molecular Sequence Data; D009865:Oocytes / Q000166:cytology / Q000502:physiology; D018408:Patch-Clamp Techniques; D010641:Phenotype; D010802:Phylogeny; D011188:Potassium / Q000378:metabolism*; D015800:Protozoan Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D014346:Trypanosoma brucei brucei / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D014370:Tsetse Flies / Q000378:metabolism / Q000469:parasitology; D014982:Xenopus laevis
D027682:Cation Transport Proteins; C552283:HKT1 protein, Trypanosoma brucei; D015800:Protozoan Proteins; D011188:Potassium