title: TbIRK is a signature sequence free potassium channel from Trypanosoma brucei locating to acidocalcisomes.
abstract: Potassium channels from prokaryotes and eukaryotes are usually recognized by a typical amino acid sequence TXTGY(F)G representing the ionic selectivity filter. Using a screening approach with ion channel family profiles but without the above motif, we identified a gene in Trypanosoma brucei that exhibits homology to inward rectifying potassium channels. We report here cloning of this ion channel named TbIRK. The protein is localized to acidocalcisomes in procyclic and in bloodstream form parasites. Functional properties of this channel were established after expression in Xenopus oocytes. Currents recorded in potassium medium show inward rectification and little time dependence. Surprisingly, this channel retains selectivity for potassium ions over sodium ions >7, in spite of the lack of the classical selectivity filter. The sequence GGYVG was predicted in silico to replace this filter motif. Point mutations of the corresponding glycine residues confirmed this at the functional level. The channel is inhibited by caesium ions but remains unaffected by barium ions up to 10 mM. TbIRK is to our knowledge the first potassium channel in T. brucei that localizes to the acidocalcisomes, organelles involved in the storage of phosphates and the response to osmotic stress that occurs during the life cycle of trypanosomes.
authors.affiliation: Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Steinmann
authors.affiliation: Swiss Tropical and Public Health Institute, Basel, Switzerland.|University of Basel, Basel, Switzerland.
authors.forename: Remo S
authors.identifier: http://orcid.org/0000-0002-6599-9201
authors.initials: RS
authors.lastname: Schmidt
authors.affiliation: Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Bütikofer
authors.affiliation: Swiss Tropical and Public Health Institute, Basel, Switzerland.|University of Basel, Basel, Switzerland.
authors.forename: Pascal
authors.initials: P
authors.lastname: Mäser
authors.affiliation: Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland. sigel@ibmm.unibe.ch.
authors.forename: Erwin
authors.initials: E
authors.lastname: Sigel
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D055724:Electrophysiological Phenomena; D015870:Gene Expression; D005786:Gene Expression Regulation; D015640:Ion Channel Gating; D009865:Oocytes / Q000378:metabolism; D017354:Point Mutation; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D017422:Sequence Analysis, DNA; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D024661:Potassium Channels, Inwardly Rectifying