Interaction of mammalian and plant H⁺/sucrose transporters with 14-3-3 proteins

The solute carrier 45 family (SLC45) was defined in the course of the Human Genome Project and consists of four members, A1–A4, which show only 20–30% identity of amino acid sequences among each other. All these members exhibit an identity of ∼20% to plant H⁺/sucrose cotransporters. Recently, we expressed members of the murine SLC45 family in yeast cells and demonstrated that they are, like their plant counterparts, H⁺/sucrose cotransporters. In contrast with the plant proteins, SLC45 transporters recognise also the monosaccharides glucose and fructose as physiological substrates and seem to be involved in alternative sugar supply as well as in osmoregulation of several mammalian tissues. In the present study, we provide novel insights into the regulation of SLC45 transporters. By screening for interaction partners, we found a 14-3-3 protein as a promising candidate for control of transport activity. Indeed, co-expression of the gamma isoform of murine 14-3-3 protein in yeast and Xenopus oocytes led to a significant decrease in transport rates of the murine SLC45 transporters as well as of the plant H⁺/sucrose transporter Sut1.