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J. Biol. Chem., Vol. 279, Issue 38, 39838-39845, September 17, 2004

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A Novel Phosphoglucose Isomerase (PGI)/Phosphomannose Isomerase from the Crenarchaeon Pyrobaculum aerophilum Is a Member of the PGI Superfamily

STRUCTURAL EVIDENCE AT 1.16-Å RESOLUTION^*

Michael K. Swan, Thomas Hansen, Peter Schönheit, and Christopher Davies¶

From the Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina 29425 and Institut für Allgemeine Mikrobiologie, Christian-Albrechts-Universität Kiel, D-24118 Kiel, Germany

The crystal structure of a dual specificity phosphoglucose isomerase (PGI)/phosphomannose isomerase from Pyrobaculum aerophilum (PaPGI/PMI) has been determined in native form at 1.16-Å resolution and in complex with the enzyme inhibitor 5-phosphoarabinonate at 1.45-Å resolution. The similarity of its fold, with the inner core structure of PGIs from eubacterial and eukaryotic sources, confirms this enzyme as a member of the PGI superfamily. The almost total conservation of amino acids in the active site, including the glutamate base catalyst, shows that PaPGI/PMI uses the same catalytic mechanisms for both ring opening and isomerization for the interconversion of glucose 6-phosphate (Glc-6-P) to fructose 6-phosphate (Fru-6-P). The lack of structural differences between native and inhibitor-bound enzymes suggests this activity occurs without any of the conformational changes that are the hallmark of the well characterized PGI family. The lack of a suitable second base in the active site of PaPGI/PMI argues against a PMI mechanism involving a trans-enediol intermediate. Instead, PMI activity may be the result of additional space in the active site imparted by a threonine, in place of a glutamine in other PGI enzymes, which could permit rotation of the C-2—C-3 bond of mannose 6-phosphate.

Received for publication, June 18, 2004 , and in revised form, July 12, 2004.

The atomic coordinates and structure factors (codes 1TZB and 1TZC) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

^* The work was supported in part by Deutsche Forschungsgemeinschaft by Grant SCHO 316/9-1 (to P. S.). 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.

^¶ To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, Medical University of South Carolina, 173 Ashley Ave., Charleston, SC 29425. Tel.: 843-792-1468; Fax: 843-792-8568; E-mail: davies{at}musc.edu.

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