title: Size does matter: 18 amino acids at the N-terminal tip of an amino acid transporter in Leishmania determine substrate specificity.
abstract: Long N-terminal tails of amino acid transporters are known to act as sensors of the internal pool of amino acids and as positive regulators of substrate flux rate. In this study we establish that N-termini of amino acid transporters can also determine substrate specificity. We show that due to alternative trans splicing, the human pathogen Leishmania naturally expresses two variants of the proline/alanine transporter, one 18 amino acid shorter than the other. We demonstrate that the longer variant (LdAAP24) translocates both proline and alanine, whereas the shorter variant (∆18LdAAP24) translocates just proline. Remarkably, co-expressing the hydrophilic N-terminal peptide of the long variant with ∆18LdAAP24 was found to recover alanine transport. This restoration of alanine transport could be mediated by a truncated N-terminal tail, though truncations exceeding half of the tail length were no longer functional. Taken together, the data indicate that the first 18 amino acids of the negatively charged N-terminal LdAAP24 tail are required for alanine transport and may facilitate the electrostatic interactions of the entire negatively charged N-terminal tail with the positively charged internal loops in the transmembrane domain, as this mechanism has been shown to underlie regulation of substrate flux rate for other transporters.
authors.affiliation: Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Doreen
authors.initials: D
authors.lastname: Schlisselberg
authors.affiliation: Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Eldar
authors.initials: E
authors.lastname: Mazarib
authors.affiliation: Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Ehud
authors.initials: E
authors.lastname: Inbar
authors.affiliation: Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland.
authors.forename: Doris
authors.initials: D
authors.lastname: Rentsch
authors.affiliation: Seattle Biomedical Research Institute, 307 Westlake Ave N, Seattle, WA 98109-5219, USA.|Departments of Global Health &Medical Education, University of Washington, Seattle, WA 98195, USA.|Departments of Biomedical Informatics &Medical Education, University of Washington, Seattle, WA 98195, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Myler
authors.affiliation: Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Dan
authors.initials: D
authors.lastname: Zilberstein
mesh_terms: D000409:Alanine / Q000235:genetics / Q000378:metabolism; D017398:Alternative Splicing / Q000235:genetics; D000595:Amino Acid Sequence / Q000235:genetics; D026905:Amino Acid Transport Systems / Q000235:genetics*; D006801:Humans; D007891:Leishmania / Q000235:genetics* / Q000472:pathogenicity; D007896:Leishmaniasis / Q000235:genetics* / Q000469:parasitology / Q000473:pathology; D011392:Proline / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D026905:Amino Acid Transport Systems; D011392:Proline; D000409:Alanine