High impact information on STP1

• The definite proof for the function of the STP1 protein as a hexose transporter and data on its substrate specificity were obtained by heterologous expression in the fission yeast Schizosaccharomyces pombe [1].
• By complementation of the mutant, immunological analysis, and analysis of starch phosphorylation, we show that sex1 is defective in the Arabidopsis homolog of the R1 protein and not in the hexose transporter [2].
• This transporter, initially characterized more than 20 years ago, is closely related to the mammalian glucose transporter GLUT family and differs from all other plant hexose transporters that have been characterized to date [3].
• SGB1 is shown here to be a Golgi-localized hexose transporter and acts genetically with AGB1 in early seedling development [4].
• Here we provide evidence that AtUTr1, a UDP-galactose/glucose transporter from Arabidopsis thaliana, responds to stimuli that trigger the UPR increasing its expression around 9-fold [5].

Biological context of STP1

• Steady-state and presteady-state kinetics of the H+/hexose cotransporter (STP1) from Arabidopsis thaliana expressed in Xenopus oocytes [6].
• Our data suggest a function of AtSTP1 in monosaccharide import into guard cells during the night and a possible role in osmoregulation during the day [7].
• Atstp1 seedlings grow effectively on concentrations of D-galactose that inhibit wild-type growth, even at up to 100 mM D-galactose, indicating that active transport by AtSTP1 plays a major role at very high concentrations of exogenous sugar [8].
• We used a kinematic method to quantify the spatial distribution of the rate and extent of cell division and expansion, and we compared stp1 with wild type and with wild type treated with exogenous cytokinin (1 microM zeatin) or auxin (30 nM 2,4-dichlorophenoxyacetic acid) [9].
• Expression of the Arabidopsis high-affinity hexose transporter STP13 correlates with programmed cell death [10].

Anatomical context of STP1

• We have investigated the steady-state and presteady-state kinetics of the cloned H+/hexose cotransporter from Arabidopsis thaliana (STP1) expressed in Xenopus oocytes using the two-electrode voltage-clamp method [6].
• Detergent extracts from either total membranes or plasma membranes of transgenic yeast cells were used for one-step purification of the STP1-His6 protein on Ni(2+)-NTA columns [11].
• It is suggested that in mutant TC265 the primary lesion is in a hexose transporter in the chloroplast envelope, and that this transporter moves the products of starch breakdown that are destined for sucrose synthesis from the chloroplast to the cytosol [12].

Associations of STP1 with chemical compounds

• The sugar specificity of STP1 was D-mannose > or = 2-deoxyglucose > D-galactose > or = 3OMG > D-xylose > D-glucose > D-fucose > D-fructose > L-glucose > L-arabinose > D-arabinose, demonstrating that STP1 has a low substrate specificity [6].
• At saturating 3OMG and at low external [H+] (pH 7.5), the transient STP1 currents were eliminated [6].
• This transient increase in AtSTP1 expression correlates in time with the described guard cell-specific accumulation of sucrose [7].
• AtSTP1 transports glucose, galactose, xylose, and mannose, but not fructose [13].

Analytical, diagnostic and therapeutic context of STP1

• Expression of the AtSTP1 H+-monosacharide symporter gene in guard cells was demonstrated by in situ hybridization and by immunolocalization with an AtSTP1-specific antiserum [7].

References