Mathieu C et al. (2017), Arginine and Lysine Transporters Are Essential ...

XB-ART-53951

PLoS One 2017 Jan 03;121:e0168775. doi: 10.1371/journal.pone.0168775.

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Arginine and Lysine Transporters Are Essential for Trypanosoma brucei.

Mathieu C , Macêdo JP , Hürlimann D , Wirdnam C , Haindrich AC , Suter Grotemeyer M , González-Salgado A , Schmidt RS , Inbar E , Mäser P , Bütikofer P , Zilberstein D , Rentsch D .

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For Trypanosoma brucei arginine and lysine are essential amino acids and therefore have to be imported from the host. Heterologous expression in Saccharomyces cerevisiae mutants identified cationic amino acid transporters among members of the T. brucei AAAP (amino acid/auxin permease) family. TbAAT5-3 showed high affinity arginine uptake (Km 3.6 ± 0.4 μM) and high selectivity for L-arginine. L-arginine transport was reduced by a 10-times excess of L-arginine, homo-arginine, canavanine or arginine-β-naphthylamide, while lysine was inhibitory only at 100-times excess, and histidine or ornithine did not reduce arginine uptake rates significantly. TbAAT16-1 is a high affinity (Km 4.3 ± 0.5 μM) and highly selective L-lysine transporter and of the compounds tested, only L-lysine and thialysine were competing for L-lysine uptake. TbAAT5-3 and TbAAT16-1 are expressed in both procyclic and bloodstream form T. brucei and cMyc-tagged proteins indicate localization at the plasma membrane. RNAi-mediated down-regulation of TbAAT5 and TbAAT16 in bloodstream form trypanosomes resulted in growth arrest, demonstrating that TbAAT5-mediated arginine and TbAAT16-mediated lysine transport are essential for T. brucei. Growth of induced RNAi lines could partially be rescued by supplementing a surplus of arginine or lysine, respectively, while addition of both amino acids was less efficient. Single and double RNAi lines indicate that additional low affinity uptake systems for arginine and lysine are present in T. brucei.

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Species referenced: Xenopus laevis
Genes referenced: myc tert

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	Fig 1. Phenogram of T. brucei amino acid transporters.Phylogenetic relationship of members of the T. brucei TREU 927 AAT5 (Tb927.8.4700-4740) and AAT16 (Tb927.11.15840, Tb927.11.15860) families and characterized arginine and lysine transporters from T. cruzi and L. donovani: TcAAAP411, (TcCLB.511411.30 [23]), TcAAP7 (TcCLB.511545.80 [24]), TcCAT1.1, TcCAT1.2, TcCAT1.3 (TcCLB.506153.10, TcCLB.506153.20, TcCLB.506053.10 [25]); LdAAP7 (LdBPK_322800.1 [24]) and LdAAP3 (LdBPK_310910.1 [22]). Further shown are AAP7 in L. major, LmAAP7 (LmjF.32.2660); the characterized, but more distantly related transporter of eflornithine and neutral amino acids, TbAAT6 (Tb927.8.5450, [18–21]); an annotated fragment with high similarity to TcCAT1.1 (TcCLB.506053.5). Scale bar represents substitutions per site.
	Fig 2. TbAAT5 and TbAAT16 mediate growth of S. cerevisiae mutants on arginine, lysine and/or histidine.Growth of S. cerevisiae mutants transformed with the vector pDR197 or pDR197 harboring different members of the T. brucei (A) AAT5 and (B) AAT16 family. S. cerevisiae was grown for 3 days on non-selective (left) and selective (right) medium. Strains allow selection for arginine (21.983c), histidine (JT16) and lysine (22Δ6AAL) transport, respectively. Lysine supplemented as lys-asp dipeptide was used as source of lysine in the non-selective medium for strain 22Δ6AAL.
	Fig 3. TbAAT5-3 mediated arginine and TbAAT16-1 mediated lysine transport are pH-dependent.(A) L-Arginine uptake rates in S. cerevisiae 21.983c expressing TbAAT5-3 were measured using 50 μM L-arginine and pH values between pH 4.5 and 7 (n = 3 ± SD). (B) TbAAT16-1-mediated 50 μM L-lysine transport at pH 4.5, 5.5, 6.5 and 7.5. Values correspond to the mean ± SD of at least seven independent experiments. Transport rates were determined as described in Materials and Methods. Relative transport rates were calculated by normalizing maximum values of each experiment to 100%.
	Fig 4. Arginine-induced currents in TbAAT5-3-expressing oocytes in the presence or absence of Na+ and K+.Oocytes were clamped at -80 mV. Inward currents were recorded upon superfusion of H2O-injected oocytes (A) and TbAAT5-1 injected oocytes (B) with Na+-Ringer containing 50 μM arginine at pH 7.4 (B). (C) Currents evoked by 20 μM arginine in sodium Ringer or choline Ringer (without sodium and potassium) at Vm of -80 mV. Mean values ± SE of 5 oocytes. Spikes in the current traces (marked by stars) are due to changes of solutions.
	Fig 5. Transport kinetics of TbAAT5-1 and TbAAT16-1.Kinetics of arginine (A) or lysine (B) uptake by TbAAT5-1 or TbAAT16-1 expressing S. cerevisiae strain 21.983c or 22Δ7AA, respectively. Representative graphs are shown. Affinities (Km) are mean values ± SD of three independent experiments.
	Fig 6. Expression of TbAAT5 and TbAAT16 members in PCF and BSF T. brucei.TbAAT5 and TbAAT16 mRNA abundance in PCF and BSF T. brucei was quantified by qRT-PCR using telomerase reverse transcriptase (TERT, Tb927.11.10190) as reference gene. Due to high homology of ORFs and UTRs (S1 Fig) only Tb427.08.4700 could be discriminated from the other TbAAT5 members (i.e. Tb427.08.4710, Tb427.08.4720, Tb427.08.4730, Tb427.08.4740). The two TbAAT16 genes (Tb427tmp.01.7500 and Tb427tmp.01.7520) were not differentiated.
	Fig 7. Localization of cMyc-TbAAT5-1 and cMyc-TbAAT16-1 in PCF T. brucei.Confocal microscopy of procyclic T. brucei cells over-expressing N-terminally cMyc-tagged versions of TbAAT5-1 and TbAAT16-1. The proteins localized in a bright ring along the periphery of the cell body and in internal membranes, showing partial localization at the plasma membrane as well as in internal membranes of unknown identity. Anti-cMyc (green); DAPI (blue); bright field image (grey); scale bar: 5 μM. The insets show Western blot analyses of extracts from uninduced (-tet) or induced (+tet) cells probed with anti-cMyc antibody. Ponceau (Ponc) staining is shown as loading control.
	Fig 8. Growth curves of TbAAT5-RNAi and TbAAT16-RNAi T. brucei BSF.Cumulative growth of T. brucei BSF control (A) or after down-regulation of TbAAT5 (B), TbAAT16 (C) or both (D) for 5 days in HMI-9. 5 mM arginine and/or 10 mM lysine was added as indicated above the growth curves. Data points of growth curves correspond to mean values ± SD from three independent experiments. Insets show mRNA levels relative to telomerase reverse transcriptase (TERT, Tb927.11.10190) transcripts after one day of induction as determined by qRT-PCR. Expression in the absence of tetracycline was set as 100%. Data points correspond to mean values ± SD from three independent experiments.

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Aslett, TriTrypDB: a functional genomic resource for the Trypanosomatidae. 2010, Pubmed