Functional characterization of apicomplexan (Plasmodium vivax) hexose transporter

초록

Apicomplexan parasite include the causative agents of malaria and toxoplasmosis. When they evolved from free-living form to intracellular parasite, they lost many biosynthetic pathways and became reliant on their hosts as a nutrient source. They take up nutrients from their host cell through membranous transporters. To understand the hexose transport in Plasmodium vivax, we have carried out cloning and functional characterization of P. vivax hexose transporter 1 (PvHT1). The PvHT1 gene from NCBI database was isolated using reverse transcription and overlap extension PCR. The isolated PvHT1 cDNA consisted of 1,509 base pairs that encoded a 502 amino acids. Membrane topology analysis showed 12 putative membrane-spanning domains. When expressed in Xenopus laevis oocytes, PvHT1 mediated the transport of tritium labeled deoxy-D-glucose (ddGlu) in an expression time-, incubation time-dependent and sodium independent manners. The PvHT1 showed no exchange mode for unlabelling glucose by efflux experiments. The kinetic analysis results showed saturable properties following Michaelis- Menten equation. The Eadie-Hofstee equation analysis revealed a Km value of 294.1 uM and Vmax value of 1,060 pmol/ oocyte/hr for ddGlu. The ddGlu uptake was strongly inhibited by glucose, mannose and ddGlu and mild effect by methyl-dglucose. These results may give information for the molecular biological study of carbohydrate metabolism in Plasmodium vivax.