Abstract
BackgroundTrypanosoma cruzi, the etiological agent of Chagas disease, is auxotrophic for arginine. It obtains this amino acid from the host through transporters expressed on the plasma membrane and on the membranes of intracellular compartments. A few cationic amino acid transporters have been characterized at the molecular level, such as the novel intracellular arginine/ornithine transporter, TcCAT1.1, a member of the TcCAT subfamily that is composed of four almost identical open reading frames in the T. cruzi genome.MethodsThe functional characterization of the TcCAT1.1 isoform was performed in two heterologous expression systems. TcCAT subfamily expression was evaluated by real-time PCR in polysomal RNA fractions, and the cellular localization of TcCAT1.1 fused to EGFP was performed by confocal and immunoelectron microscopy.ResultsIn the S. cerevisiae expression system, TcCAT1.1 showed high affinity for arginine (Km = 0.085 ± 0.04 mM) and low affinity for ornithine (Km = 1.7 ± 0.2 mM). Xenopus laevis oocytes expressing TcCAT1.1 showed a 7-fold increase in arginine uptake when they were pre-loaded with arginine, indicating that transport is enhanced by substrates on the trans side of the membrane (trans-stimulation). Oocytes that were pre-loaded with [3H]-arginine displayed a 16-fold higher efflux of [3H]-arginine compared with that of the control. Analysis of polysomal RNA fractions demonstrated that the expression of members of the arginine transporter TcCAT subfamily is upregulated under nutritional stress and that this upregulation precedes metacyclogenesis. To investigate the cellular localization of the transporter, EGFP was fused to TcCAT1.1, and fluorescence microscopy and immunocytochemistry revealed the intracellular labeling of vesicles in the anterior region, in a network of tubules and vesicles.ConclusionsTcCAT1.1 is a novel arginine/ornithine transporter, an exchanger expressed in intracellular compartments that is physiologically involved in arginine homeostasis throughout the T. cruzi life cycle. The properties and estimated kinetic parameters of TcCAT1.1 can be extended to other members of the TcCAT subfamily.
Highlights
Trypanosoma cruzi, the etiological agent of Chagas disease, is auxotrophic for arginine
TcCAT is a subfamily of the amino acid/auxin permease (AAAP) family according to the Transporter Classification Database (TCDB), a curated dataset resource composed of transporter sequences from various organisms [43]
The residues Glu369 and Asn381 are associated with increased affinity for L-ornithine, L-arginine, and L-lysine in hCAT-1, hCAT-2B, and hCAT-3, and a region of 80 amino acid sequences in length in hCAT members is associated with trans-stimulation properties
Summary
Trypanosoma cruzi, the etiological agent of Chagas disease, is auxotrophic for arginine. It obtains this amino acid from the host through transporters expressed on the plasma membrane and on the membranes of intracellular compartments. Arginine is acquired from the host through biochemically characterized high- and low-affinity transport systems on the parasite plasma membrane [5, 6]. The metacyclic trypomastigote forms released with vector excrement next to the bite wound can infect most tissues [7], and upon entry into cells, they transform into replicative amastigotes. Bloodstream trypomastigotes within mammalian hosts can be taken up by bloodsucking insects and transformed into epimastigotes, which replicate in the insect midgut and develop into pathogenic metacyclic trypomastigote forms [8, 9]. Several intermediate stages are completed, but the primary developmental stages in the T. cruzi life cycle involve the epimastigote, amastigote, and infective trypomastigote forms [10, 11]
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