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J. Biol. Chem., Vol. 280, Issue 32, 29073-29079, August 12, 2005
The Crystal Structure of Mlc, a Global Regulator of Sugar Metabolism in Escherichia coli*![]() From the Department of Biology, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany Mlc from Escherichia coli is a transcriptional repressor controlling the expression of a number of genes encoding enzymes of the phosphotransferase system (PTS), including ptsG and manXYZ, the specific enzyme II for glucose and mannose PTS transporters. In addition, Mlc controls the transcription of malT, the gene of the global activator of the mal regulon. The inactivation of Mlc as a repressor is mediated by binding to an actively transporting PtsG (EIICBGlc). Here we report the crystal structure of Mlc at 2.7 Å resolution representing the first described structure of an ROK (repressors, open reading frames, and kinases) family protein. Mlc forms stable dimers thus explaining its binding affinity to palindromic operator sites. The N-terminal helix-turn-helix domain of Mlc is stabilized by the amphipathic C-terminal helix implicated earlier in EIICBGlc binding. Furthermore, the structure revealed a metal-binding site within the cysteine-rich ROK consensus motif that coordinates a structurally important zinc ion. A strongly reduced repressor activity was observed when two of the zinc-coordinating cysteine residues were exchanged against serine or alanine, demonstrating the role of zinc in Mlc-mediated repressor function. The structures of a putative fructokinase from Bacillus subtilis, the glucokinase from Escherichia coli, and a glucomannokinase from Arthrobacter sp. showed high structural homology to the ROK family part of Mlc.
Received for publication, April 18, 2005 , and in revised form, May 31, 2005. The atomic coordinates and structure factors (code 1Z6R) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/). * This work was supported by the Deutsche Forschungsgemeinschaft. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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