HEXOSE UPTAKE IN TRYPANOSOMA-CRUZI - STRUCTURE-ACTIVITY RELATIONSHIP BETWEEN SUBSTRATE AND TRANSPORTER

The gene encoding a hexose transporter, TcrHT1, from Trypanosoma cruzi has been functionally expressed in mammalian Chinese hamster ovary ce lls. Kinetic parameters of the heterologously expressed protein are ve ry similar to those of the transporter identified in T. cruzi epimasti gotes, confirming that TcrHT1 is the major transporter functioning in these para sites. A detailed analysis of substrate recognition using a nalogues of D-glucose substituted at each carbon position has been per formed. The glucose transporter of T. cruzi does not recognize C-3 or C-6 analogues of D-glucose, whereas these analogues were recognized by the glucose transporter of bloodstream-form T. brucei. As for other k inetoplastid transporters, but in stark contrast to the mammalian GLUT family, TcrHT1 can also transport D-fructose, with relatively high af finity (K-m = 0.682+/-0.003 mM). Amino acid side-chain-modifying reage nts were also used to identify residues of the transporter present at the substrate-binding site. While specific modifiers of cysteine, hist idine and arginine all inhibited catalytic activity, protection using substrate was only observed using the arginine-specific reagent, pheny lglyoxal. Reagents which modify lysine residues had no effect on trans port.