Mlc of Thermus thermophilus: a glucose-specific regulator for a glucose/mannose ABC transporter in the absence of the phosphotransferase system.
We report the presence of Mlc in a thermophilic bacterium. Mlc is known as a global regulator of sugar metabolism in gram-negative enteric bacteria that is controlled by sequestration to a glucose-transporting EII(Glc) of the phosphotransferase system (PTS). Since thermophilic bacteria do not possess PTS, Mlc in Thermus thermophilus must be differently controlled. DNA sequence alignments between Mlc from T. thermophilus (Mlc(Tth)) and Mlc from E. coli (Mlc(Eco)) revealed that Mlc(Tth) conserved five residues of the glucose-binding motif of glucokinases. Here we show that Mlc(Tth) is not a glucokinase but is indeed able to bind glucose (K(D) = 20 microM), unlike Mlc(Eco). We found that mlc of T. thermophilus is the first gene within an operon encoding an ABC transporter for glucose and mannose, including a glucose/mannose-binding protein and two permeases. malK1, encoding the cognate ATP-hydrolyzing subunit, is located elsewhere on the chromosome. The system transports glucose at 70 degrees C with a K(m) of 0.15 microM and a V(max) of 4.22 nmol per min per ml at an optical density (OD) of 1. Mlc(Tth) negatively regulates itself and the entire glucose/mannose ABC transport system operon but not malK1, with glucose acting as an inducer. MalK1 is shared with the ABC transporter for trehalose, maltose, sucrose, and palatinose (TMSP). Mutants lacking malK1 do not transport either glucose or maltose. The TMSP transporter is also able to transport glucose with a K(m) of 1.4 microM and a V(max) of 7.6 nmol per min per ml at an OD of 1, but it does not transport mannose.
Chevance
Fabienne F V
FF
Department of Biology, University of Konstanz, 78457 Konstanz, Germany.
Erhardt
Marc
M
Lengsfeld
Christina
C
Lee
Sung-Jae
SJ
Boos
Winfried
W
D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001692:Biological Transport / Q000235:genetics; D017124:Conserved Sequence; D029968:Escherichia coli Proteins / Q000235:genetics; D017353:Gene Deletion; D023061:Gene Order; D005809:Genes, Regulator; D005947:Glucose / Q000378:metabolism*; D008358:Mannose / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009876:Operon / Q000235:genetics; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D016963:Thermus thermophilus / Q000235:genetics / Q000378:metabolism*; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C068021:MalK protein, Bacteria; D026901:Membrane Transport Proteins; C111065:Mlc protein, E coli; D012097:Repressor Proteins; D001616:beta-Galactosidase; D005947:Glucose; D008358:Mannose