title: Substrate specificity of the Arabidopsis thaliana sucrose transporter AtSUC2.
abstract: The Arabidopsis sucrose transporter AtSUC2 is expressed in the companion cells of the phloem (specialized vascular tissue) and is essential for the long distance transport of carbohydrates within the plant. A variety of glucosides are known to inhibit sucrose uptake into yeast expressing AtSUC2; however, it remains unknown whether glucosides other than sucrose could serve as transported substrates. By expression of AtSUC2 in Xenopus oocytes and two-electrode voltage clamping, we have tested the ability of AtSUC2 to transport a range of physiological and synthetic glucosides. Sucrose induced inward currents with a K0.5 of 1.44 mM at pH 5 and a membrane potential of -137 mV. Of the 24 additional sugars tested, 8 glucosides induced large inward currents allowing kinetic analysis. These glucosides were maltose, arbutin (hydroquinone-beta-D-glucoside), salicin (2-(hydroxymethyl)phenyl-beta-D-glucoside), alpha-phenylglucoside, beta-phenylglucoside, alpha-paranitrophenylglucoside, beta-paranitrophenylglucoside, and paranitrophenyl-beta-thioglucoside. In addition, turanose and alpha-methylglucoside induced small but significant inward currents indicating that they were transported by At-SUC2. The results indicate that AtSUC2 is not highly selective for alpha-over beta-glucosides and may function in transporting glucosides besides sucrose into the phloem, and the results provide insight into the structural requirements for transport by AtSUC2.
authors.affiliation: Department of Plant Biology, University of Minnesota Twin Cities, St. Paul, Minnesota 55108, USA.
authors.forename: Divya
authors.initials: D
authors.lastname: Chandran
authors.forename: Anke
authors.initials: A
authors.lastname: Reinders
authors.forename: John M
authors.initials: JM
authors.lastname: Ward
mesh_terms: D000818:Animals; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001104:Arbutin / Q000378:metabolism / Q000494:pharmacology; D001592:Benzyl Alcohols / Q000378:metabolism / Q000494:pharmacology; D002236:Carbohydrate Conformation; D004553:Electric Conductivity; D005260:Female; D015870:Gene Expression; D005960:Glucosides / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D008320:Maltose / Q000378:metabolism / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D013395:Sucrose / Q000494:pharmacology; D014162:Transfection; D014982:Xenopus laevis
chemical_list: D029681:Arabidopsis Proteins; D001592:Benzyl Alcohols; D005960:Glucosides; D026901:Membrane Transport Proteins; D010940:Plant Proteins; C078729:sucrose transport protein, plant; C005696:salicin; D013395:Sucrose; D008320:Maltose; D001104:Arbutin