Function of the cytosolic N-terminus of sucrose transporter AtSUT2 in substrate affinity.
AtSUT2 was found to be a low-affinity sucrose transporter (K(M)=11.7 mM at pH 4). Chimeric proteins between AtSUT2 and the high-affinity StSUT1 were constructed in which the extended N-terminus and central loop of AtSUT2 were exchanged with those domains of StSUT1 and vice versa. Chimeras containing the N-terminus of AtSUT2 showed significantly lower affinity for sucrose compared to chimeras containing the N-terminus of StSUT1. The results indicate a significant function of the N-terminus but not the central cytoplasmic loop in determining substrate affinity. Expression of AtSUT2 in major veins of source leaves and in flowers is compatible with a role as a second low-affinity sucrose transporter or as a sucrose sensor.
Schulze
W
W
Plant Physiology, ZMBP, Universität Tübingen, Auf der Morgenstelle 1, 72076 Tübingen, Germany.
Weise
A
A
Frommer
W B
WB
Ward
J M
JM
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000737:chemistry / Q000235:genetics; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry*; D015870:Gene Expression; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000235:genetics; D013395:Sucrose / Q000378:metabolism
D002352:Carrier Proteins; D026901:Membrane Transport Proteins; D010446:Peptide Fragments; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; C078729:sucrose transport protein, plant; D013395:Sucrose