Exploring the function of Plasmodium vivax Hexose Transporter 1 (PvHT1)

초록

Introduction : Plasmodium vivax is the most widely distributed human malaria parasites. The eradication of vivax malaria remains in challenging due to transmission of the drug-resistant parasite and dormant liver form. Consequently, anti-malarial drugs with novel mechanisms of action are urgently demanded. The glucose uptake blocking strategy was suggested for novel mode of action that lead to selective starvation of parasites. The hexose transporter 1 was identified for glucose uptake as an essential nutrient in various Plasmodium species. In this study, we focused on P. vivax hexose transperter 1 (PvHT1) to identify precise properties of glucose uptake. Materials and Methods : A cDNA encoding a PvHT1 was isolated from the whole blood infected with P. vivax, and functional characterization was performed using Xenopus laevis oocyte expression system. Results : PvHT1-expressed Xenopus laevis oocytes mediated the transport of [3H]deoxy-D-glucose (ddGlu) in an expression and incubation time-dependent manner without sodium dependency. PvHT1 showed no exchange mode of glucose in efflux experiments and concentration-dependent results showed saturable kinetics following the Michaelis-Menten equation. The Eadie-Hofstee equation analysis revealed a Km value of 294.1 μM and a Vmax value of 1,060 pmol/oocyte/hr. The inhibition experiments showed a strong inhibitory effect by glucose, mannose, and ddGlu, and a moderate effect by methyl-d-glucose. Conclusions : The amino acid sequence and tertiary structure comparison between P. falciparum and P. vivax HT1 revealed a completely conserved residue in glucose binding pocket. This result supported that glucose uptake properties of P. vivax are similar with those of P. falciparum and PfHT1 inhibitor (compound 3361) work in P. vivax. Additionally, the results provide knowledge of glucose uptake via PvHT1 for carbohydrate metabolism and support approaches to vivax malaria drug development strategy on parasite starvation