Trypanosoma brucei bloodstream forms express highly specific and separate transporters for adenine and hypoxanthine; evidence for a new protozoan purine transporter family?

Publication date: March 2018 Source:Molecular and Biochemical Parasitology, Volume 220 Author(s): Gustavo D. Campagnaro, Khalid J. Alzahrani, Jane C. Munday, Harry P. De Koning The transport of nucleobases and nucleosides in protozoan parasites is known to be performed by Equilibrative Nucleoside Transporter (ENT) family members, including the extensively studied P1 and P2 nucleoside transporters of T. brucei bloodstream forms. Studies with P2 knockout parasites suggested the existence of as yet uncharacterised purine transport mechanisms in these cells. Here, we deleted several ENT genes, in addition to P2, including an array comprising three genes encoding for high-affinity broad-selectivity nucleobase transporters − the longest multi-gene locus deletion in T. brucei to date. It was verified that none of them appreciably contributed to the transport of hypoxanthine in bloodstream forms grown axenically in HMI-9 medium, which was mainly performed by a previously not described hypoxanthine-specific transporter (HXT1) with a Km of 22 ± 1.7 μM and V max of 0.49 ± 0.06 pmol(107 cells)−1 s−1. The uptake of adenine was also assessed in the knockout cells and was performed by a highly specific adenine transporter (ADET1) with a Km of 573 ± 62 nM and V max of 0.23 ± 0.06 pmol(107 cells)−1 s−1. Neither HXT1 nor ADET1 displayed any affinity for other natural purines or pyrimidines and could not be completely inhibited by hypoxanthin...
Source: Molecular and Biochemical Parasitology - Category: Parasitology Source Type: research