A Trk/HKT-Type K ⁺ Transporter from Trypanosoma brucei

Abstract

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 ؉ channelblocking 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.

Trypanocidal activity of salinomycin is due to sodium influx followed by cell swelling

“…By using the fluorescent probe 3,3’-dihexyloxycarbocyanine, however, it was found that salinomycin did not affect the membrane potential of bloodstream forms of T. brucei (data not shown). This observation is in agreement with previous findings that valinomycin also did not influence the membrane potential of trypanosomes, although the parasites are extremely sensitive to this ionophore [21]. …”

Cyclic Di-AMP Impairs Potassium Uptake Mediated by a Cyclic Di-AMP Binding Protein in Streptococcus pneumoniae

“…Our results showed that LB2003 was unable to grow in a minimal medium containing 2 mM KCl (not shown), similar to the observation in a previous study (44). However, the defective growth of LB2003 in this medium could be rescued by coexpression of cabP and SPD_0076 but not by the vector control (Fig.…”

Potassium and sodium uptake systems in fungi. The transporter diversity of Magnaporthe oryzae

“…In contrast, the existence of TRK or HAK transporters in eukaryotic organisms that differ from fungi and land plants seems to be infrequent, although TRK transporters have been reported in several species of Trypanosoma and Leishmania (Mosimann et al, 2010). BLAST searches using fungal TRK and HAK proteins as queries identified some TRK and HAK proteins from eukaryotes that were different from fungi and land plants.…”