Canine brain glucose transporter 3: gene sequence, phylogenetic comparisons and analysis of functional sites

There has been a sparsity of various mammalian neuronal glucose transporter 3-encoding sequences(Glut3) available for the purposes of alignment studies. We report here a 2355-bp sequence of canine Glut3 that encodes a deduced protein of 496 amino acids (aa). The full-length canine aa sequence was compared to those of the human, mouse and rat glucose transporter 3 (Glut3), and found to be 88.3, 84.9 and 84.3% identical, respectively. However, while mouse and rat identical C-termini, the canine nd human C-termini share markedly little identity or similarity to one another, or to that of rat/mouse. The canine Glut3 sequence also exhibits 74.5% aa identity with a non-mammalian chicken Glut3 sequence. These differences in the C-termini of Glut3 among the species may result in kinetic or mechanistic differences in transport of glucose. Computer searches were made for conserved functional motifs, and a brief review of ten sites is provided. This review includes the determination of their locations in two transmembrane (TM) motifs that have been proposed for glucose transporters. The nucleotide (nt) sequence of the 5'-untranslated region (UTR) of canine Glut3 was aligned with the comparable human glut3 region and was shown to be 70% identical over a region of 129 nt just prior to the ATG start codons. A similar comparison of the 3'-UTR shows 74% identity over 350 nt immediately following the stop codons. An adenosine-uridine-binding factor (AUBF) region, which has been identified as a region of importance in mRNA stabilization, is conserved in the 3'-UTR of both canine and human Glut3. The conservation in the UTR suggests that Glut3 may be post-transcriptionally regulated.