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J. Biol. Chem., Vol. 282, Issue 37, 27334-27342, September 14, 2007

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High Resolution Crystal Structures of Mycobacterium tuberculosis Adenosine Kinase

INSIGHTS INTO THE MECHANISM AND SPECIFICITY OF THIS NOVEL PROKARYOTIC ENZYME^*

From the Department of Biochemistry & Biophysics, Texas A&M University, College Station, Texas 77843

Adenosine kinase (ADK) catalyzes the phosphorylation of adenosine (Ado) to adenosine monophosphate (AMP). It is part of the purine salvage pathway that has been identified only in eukaryotes, with the single exception of Mycobacterium spp. Whereas it is not clear if Mycobacterium tuberculosis (Mtb) ADK is essential, it has been shown that the enzyme can selectively phosphorylate nucleoside analogs to produce products toxic to the cell. We have determined the crystal structure of Mtb ADK unliganded as well as ligand (Ado) bound at 1.5- and 1.9-Å resolution, respectively. The structure of the binary complexes with the inhibitor 2-fluoroadenosine (F-Ado) bound and with the adenosine 5'-(,-methylene)triphosphate (AMP-PCP) (non-hydrolyzable ATP analog) bound were also solved at 1.9-Å resolution. These four structures indicate that Mtb ADK is a dimer formed by an extended sheet. The active site of the unliganded ADK is in an open conformation, and upon Ado binding a lid domain of the protein undergoes a large conformation change to close the active site. In the closed conformation, the lid forms direct interactions with the substrate and residues of the active site. Interestingly, AMP-PCP binding alone was not sufficient to produce the closed state of the enzyme. The binding mode of F-Ado was characterized to illustrate the role of additional non-bonding interactions in Mtb ADK compared with human ADK.

Received for publication, April 19, 2007 , and in revised form, May 31, 2007.

The atomic coordinates and structure factors (codes 2PKF, 2PKM, 2PKK, and 2PKN) 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 Structural Genomics of Persistence Targets from Mycobacterium tuberculosis Grant PO1 AI 68135 from the National Institutes of Health, R. J. Wolfe-Welch Foundation Chair in Science Grants A-0015, and NSF-0521553. 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.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Tables S1-S2 and Figs. S1-S2.

¹ Both authors contributed equally to this work.

² To whom correspondence should be addressed. Tel.: 979-862-7636; Fax: 979-862-7638; E-mail: sacchett{at}tamu.edu.

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