KINETOPLASTID GLUCOSE TRANSPORTERS

Protozoa of the order kinetoplastida have colonized many habitats, and several species are important parasites of humans. Adaptation to diff erent environments requires an associated adaptation at a cell's inter face with its environment, i.e. the plasma membrane. Sugar transport b y the kinetoplastida as a phylogenetically related group of organisms offers an exceptional model in which to study the ways by which the ca rrier proteins involved in this process may evolve to meet differing e nvironmental challenges. Seven genes encoding proteins involved in glu cose transport have been cloned from several kinetoplastid species, Th e transporters all belong to the glucose transporter superfamily exemp lified by the mammalian erythrocyte transporter GLUT1. Some species, s uch as the African trypanosome Trypanosoma brucei, which undergo a lif e cycle where the parasites are exposed to very different glucose conc entrations in the mammalian bloodstream and tsetse-fly midgut, have ev olved two different transporters to deal with this fluctuation. Other species, such as the South American trypanosome Trypanosoma cruzi, mul tiply predominantly in conditions of relative glucose deprivation (int racellularly in the mammalian host, or within the reduviid bug midgut) and have a single, relatively high-affinity type, transporter. All of the kinetoplastid transporters can also transport D-fructose, and are relatively insensitive to the classical inhibitors of GLUT1 transport cytochalasin B and phloretin.