Homologous sugar transport proteins in Escherichia coli and their relatives in both prokaryotes and eukaryotes

Abstract

Separate proteins for proton-linked transport of D-xylose, L-arabinose, D-galactose, L-rhamnose and L-fucose into Escherichia coli are being studied. By cloning and sequencing the appropriate genes, the amino acid sequences of proteins for D-xylose/H+ symport (XylE), L-arabinose/H+ symport (AraE), and part of the protein for D-galactose/H+ symport (GalP) have been determined. These are homologous, with at least 28% identical amino acid residues conserved in the aligned sequences, although their primary sequences are not similar to those of other E. coli transport proteins for lactose, melibiose, or D-glucose. However, they are equally homologous to the passive D-glucose transport proteins from yeast, rat brain, rat adipocytes, human erythrocytes, human liver, and a human hepatoma cell line. The substrate specificity of GalP from E. coli is similar to that of the mammalian glucose transporters. Furthermore, the activities of GalP, AraE and the mammalian glucose transporters are all inhibited by cytochalasin B and N-ethylmaleimide. Conserved residues in the aligned sequences of the bacterial and mammalian transporters are identified, and the possible roles of some in sugar binding, cation binding, cytochalasin binding, and reaction with N-ethylmaleimide are discussed. Each protein is independently predicted to form 12 hydrophobic, membrane-spanning alpha-helices with a central hydrophilic segment, also comprised of alpha-helix. This unifying structural model of the sugar transporters shares features with other ion-linked transport proteins for citrate or tetracycline.

Cloning and functional expression of a mouse liver organic cation transporter

“…Table 2 also shows that mOct1/Slc22a1-injected oocytes did not transport the inorganic cation 55 Fe ϩϩ , taurine, the organic anion taurocholate, or several sugars. [24][25][26] Finally, a Basic Local Alignment Search Tool (BLAST) search revealed sequence homology between mOct1/Slc22a1, and cDNAs and genomic DNA sequences from several other species. Using the coding region as template for probe, we employed Southern blot analysis on genomic DNA isolated from several eukaryotic species.…”

Mammalian integral membrane receptors are homologous to facilitators and antiporters of yeast, fungi, and eubacteria

“…Examination of the binary statistical analyses summarized in Table 1 reveals that the seven recognized amino acid transporters of yeast, E. coli, and fungi, i.e., Hipl, Put4, Canl, Gapl, PutX, AroP, and PheP, which presumably function by solute uniport or so1ute:cation symport (Henderson & Maiden, 1990) are the most similar (26-62% identity; binary comparison scores of 21-99 standard deviations). In contrast, the ArcD protein, which specifies an arginine/ornithine antiporter of Z?…”

“…Recently it was shown that transmembrane solute transporters fall into several families of homologous proteins (Henderson & Maiden, 1990;Higgins, 1990;Maloney, 1990;. As an increasing number of sequences becomes available, analyses are revealing the existence of more superfamilies that extend across phylogenetic lines (Reizer et al, 1990.…”

Engineering of yeast hexose transporters to transport d -xylose without inhibition by d -glucose

“…Isothermal titration calorimetry measurements have revealed that xylose and glucose bind with similar high affinities to XylE (K d Xyl = 0.35 mM vs. K d Glc = 0.77 mM) (34)(35)(36).…”