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FEBS Lett. 2000 Nov 24;485(2-3):189-94.

Function of the cytosolic N-terminus of sucrose transporter AtSUT2 in substrate affinity.

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Plant Physiology, ZMBP, Universität Tübingen, Auf der Morgenstelle 1, 72076 Tübingen, Germany.


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.

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