FUNCTIONAL EXPRESSION OF 2 GLUCOSE-TRANSPORTER ISOFORMS FROM THE PARASITIC PROTOZOAN LEISHMANIA-ENRIETTII

The parasitic protozoan Leishmania enriettii contains a family of tand emly repeated genes, designated Pro-1, that encode proteins with signi ficant sequence similarity to mammalian facilitative glucose transport ers. Pro-1 mRNAs are expressed almost exclusively in the promastigote or insect stage of the parasite life cycle. The Pro-1 tandem repeat en codes two isoforms of the putative transporter, iso-1 and iso-2, which have identical predicted amino acid sequences except for their NH2-te rminal hydrophilic domains. We have now expressed both iso-1 and iso-2 by microinjecting their RNAs into Xenopus oocytes and assaying these oocytes for transport of various radiolabeled ligands. Both iso-1 and iso-2 transport [H-3]2-deoxy-D-glucose, confirming that each protein i s a bona fide glucose transporter. Each isoform also transports fructo se and, to a much lesser degree, mannose. Compounds which inhibit 2-de oxy-D-glucose transport in L. enriettii promastigotes also inhibit tra nsport in the microinjected oocytes expressing each isoform, indicatin g that the substrate specificities and pharmacological properties of e ach isoform are similar to those measured for 2-deoxy-D-glucose transp ort in intact parasites. The K-m for transport of 2-deoxyglucose in oo cytes expressing iso-1 is similar to that for oocytes expressing iso-2 . These results reveal that both transporter isoforms have closely rel ated functional properties and that the difference in their structures may serve some other purpose such as differential subcellular localiz ation.