Diamidine transport in the kinetoplastidae

African trypanosomes are protozoan parasites that are unable to synthesise purines de novo and as a result must scavenge them from the host environment. Purines are transported into the cell via a number of surface membrane transporters that recognise specific motifs on the substrate. These transporters can be exploited to mediate the uptake of trypanocidal drugs, such as diamidines and arsenicals. The high affinity pentamidine transporter 1 (LAPT1) and the low affinity pentamidine transporter1 (LAPTl) are involved in the uptake of the diamidine compound pentamidine and the specificities and associated affinities of these transporters for various other compounds were tested by looking at the inhibitory effect of varying concentrations of test drugs on the uptake of 3H-pentamidine. A link was found between the carbon chain length of diamidine compounds and their affinity for HAPT1 and LAPT1. For compounds containing benzene and furan rings, the position of methyl groups in relation to these structures also appears to be important. HAPT1 and LAPT1 differ in ligand recognition profdes, although both are implicated here in the uptake of Isometamidium and Ethidium Bromide, two trypanocidal drugs previously thought to be taken up by diffusion only. As there is increasing drug resistance to all trypanocidal drugs, HAPT1 and LAPT1 are extremely important as alternative delivery systems for trypanocides in the event that other transporters are lost in the field through drug pressure, for example P2. The P2 transporter known to mediate the uptake of adenosine and melaminophenylarsenicals is shown here, by using transport assays in conjunction with Michaelis-Menten kinetics, to be the sole mechanism for the uptake of veterinary drug Berenil, in Trypanosoma brucei brucei. Finally, Crithidia fasciculata, another kinetoplastid, is shown to have particular attributes, which would value this organism as a potential expression system for the characterisation of HAPT1 and LAPTI