title: Transmembrane segments 1, 5, 7 and 8 are required for high-affinity glucose transport by Saccharomyces cerevisiae Hxt2 transporter.
abstract: Hxt2 is a high-affinity facilitative glucose transporter of Saccharomyces cerevisiae and belongs to the major facilitator superfamily. Hxt1 shares approximately 70% amino acid identity with Hxt2 in its transmembrane segments (TMs) and inter-TM loops, but transports D-glucose with an affinity about one-tenth of that of Hxt2. To determine which TMs of Hxt2 are important for high-affinity glucose transport, we constructed chimaeras of Hxt2 and Hxt1 by randomly replacing each of the 12 TMs of Hxt2 with the corresponding segment of Hxt1, for a total of 4096 different transporters. Among > 20000 yeast transformants screened, 39 different clones were selected by plate assays of high-affinity glucose-transport activity and sequenced. With only two exceptions, the selected chimaeras contained Hxt2 TMs 1, 5, 7 and 8. We then constructed chimaeras corresponding to all 16 possible combinations of Hxt2 TMs 1, 5, 7 and 8. Only one chimaera, namely that containing all four Hxt2 TMs, exhibited transport activity comparable with that of Hxt2. The K (m) and V (max) values for D-glucose transport, and the substrate specificity of this chimaera were almost identical with those of Hxt2. These results indicate that TMs 1, 5, 7 and 8 are necessary for exhibiting high-affinity glucose-transport activity of Hxt2.
authors.affiliation: Laboratory of Biophysics, School of Medicine, Teikyo University, Hachioji, Tokyo 192-0395, Japan.
authors.forename: Toshiko
authors.initials: T
authors.lastname: Kasahara
authors.forename: Michihiro
authors.initials: M
authors.lastname: Kasahara
mesh_terms: D032621:DNA Shuffling; D005947:Glucose / Q000378:metabolism*; D051246:Glucose Transport Proteins, Facilitative; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013379:Substrate Specificity
chemical_list: D051246:Glucose Transport Proteins, Facilitative; C090594:HXT1 protein, S cerevisiae; C084498:HXT2 protein, S cerevisiae; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D005947:Glucose