Activity and genomic organization of human glucose transporter 9 (GLUT9), a novel member of the family of sugar-transport facilitators predominantly expressed in brain and leucocytes.

The GLUT9 gene encodes a cDNA which exhibits significant sequence similarity with members of the glucose transporter (GLUT) family. The gene is located on chromosome 9q34 and consists of 10 exons separated by short introns. The amino acid sequence deduced from its cDNA predicts 12 putative membrane-spanning helices and all the motifs (sugar-transporter signatures) that have previously been shown to be essential for transport activity. A striking characteristic of GLUT9 is the presence of two arginines in the putative helices 7 and 8 at positions where the organic anion transporters harbour basic residues. The next relative of GLUT9 is the glucose transporter GLUT8/GLUTX1 (44.8% amino acid identity with GLUT9). A 2.6-kb transcript of GLUT9 was detected in spleen, peripheral leucocytes and brain. Transfection of COS-7 cells with GLUT9 produced expression of a 46-kDa membrane protein which exhibited reconstitutable glucose-transport activity and low-affinity cytochalasin-B binding. It is concluded that GLUT9 is a novel member of the family of sugar-transport facilitators with a tissue-specific function.