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Journal of Bacteriology, September 2006, p. 6561-6571, Vol. 188, No. 18
0021-9193/06/$08.00+0     doi:10.1128/JB.00715-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Mlc of Thermus thermophilus: a Glucose-Specific Regulator for a Glucose/Mannose ABC Transporter in the Absence of the Phosphotransferase System

Fabienne F. V. Chevance,{dagger} Marc Erhardt, Christina Lengsfeld, Sung-Jae Lee, and Winfried Boos*

Department of Biology, University of Konstanz, 78457 Konstanz, Germany

Received 18 May 2006/ Accepted 3 July 2006

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 EIIGlc 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 (MlcTth) and Mlc from E. coli (MlcEco) revealed that MlcTth conserved five residues of the glucose-binding motif of glucokinases. Here we show that MlcTth is not a glucokinase but is indeed able to bind glucose (KD = 20 µM), unlike MlcEco. 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°C with a Km of 0.15 µM and a Vmax of 4.22 nmol per min per ml at an optical density (OD) of 1. MlcTth 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 Km of 1.4 µM and a Vmax of 7.6 nmol per min per ml at an OD of 1, but it does not transport mannose.

* Corresponding author. Mailing address: Department of Biology, University of Konstanz, 78457 Konstanz, Germany. Phone: 49 7531 882658. Fax: 49 7531 883356. E-mail: winfried.boos{at}uni-konstanz.de.

{dagger} Present address: Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112.

Journal of Bacteriology, September 2006, p. 6561-6571, Vol. 188, No. 18
0021-9193/06/$08.00+0     doi:10.1128/JB.00715-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.





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