GLUT8, a novel member of the sugar transport facilitator family with glucose transport activity

GLUTS is a novel glucose transporter-like protein that exhibits significant sequence similarity with the members of the sugar transport facilitator fa mily (29.4% of amino acids identical with GLUT1), Human and mouse sequence (86.2% identical amino acids) comprise 12 putative membrane-spanning helice s and several conserved motifs (sugar transporter signatures), which have p reviously been shown to be essential for transport activity, e.g. GRK in lo op 2, PETPR in loop 6, QQLSGVN in helix 7, DRAGRR in loop 8, GWGPIPW in hel ix 10, and PETKG in the C-terminal tail. An expressed sequence tag (STS A00 5N15) corresponding with the 3'-untranslated region of GLUTS has previously been mapped to human chromosome 9, COS-7 cells transfected with GLUTS cDNA expressed a 42-kDa protein exhibiting specific, glucose-inhibitable cytoch alasin B binding (K-D = 56.6 +/- 18 nM) and reconstitutable glucose transpo rt activity (8.1 +/- 1.4 nmol/(mg protein x 10 s) versus 1.1 +/- 0.1 in con trol transfections), In human tissues, a 2.4-kilobase pair transcript was p redominantly found in testis, but not in testicular carcinoma. Lower amount s of the mRNA were detected in most other tissues including skeletal muscle , heart, small intestine, and brain. GLUTS mRNA was found in testis from ad ult, but not from prepubertal rats; its expression in human testis was supp ressed by estrogen treatment. It is concluded that GLUTS is a sugar transpo rt facilitator with glucose transport activity and a hormonally regulated t esticular function.