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J. Biol. Chem., Vol. 279, Issue 20, 21478-21488, May 14, 2004

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Structural Studies of the Catalytic Reaction Pathway of a Hyperthermophilic Histidinol-phosphate Aminotransferase^*

Francisco J. Fernandez, M. Cristina Vega, Frank Lehmann, Erika Sandmeier¶, Heinz Gehring¶, Philipp Christen¶, and Matthias Wilmanns||

From the EMBL Deutsches Elektronen-Synchrotron, Notkestrasse 85, Building 25A, D-22603 Hamburg, Germany and ^¶Biochemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland

In histidine biosynthesis, histidinol-phosphate aminotransferase catalyzes the transfer of the amino group from glutamate to imidazole acetol-phosphate producing 2-oxoglutarate and histidinol phosphate. In some organisms such as the hyperthermophile Thermotoga maritima, specific tyrosine and aromatic amino acid transaminases have not been identified to date, suggesting an additional role for histidinol-phosphate aminotransferase in other transamination reactions generating aromatic amino acids. To gain insight into the specific function of this transaminase, we have determined its crystal structure in the absence of any ligand except phosphate, in the presence of covalently bound pyridoxal 5'-phosphate, of the coenzyme histidinol phosphate adduct, and of pyridoxamine 5'-phosphate. The enzyme accepts histidinol phosphate, tyrosine, tryptophan, and phenylalanine, but not histidine, as substrates. The structures provide a model of how these different substrates could be accommodated by histidinol-phosphate aminotransferase. Some of the structural features of the enzyme are more preserved between the T. maritima enzyme and a related threonine-phosphate decarboxylase from S. typhimurium than with histidinol-phosphate aminotransferases from different organisms.

Received for publication, January 12, 2004 , and in revised form, February 24, 2004.

The atomic coordinates and structure factors (codes 1H1C, 1UU0, 1UU1, and 1UU2) 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 Deutsche Forschungsgemeinschaft Grants WI 1058/5-3 and WI 1058/5-4 (to M. W.). 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.

Both authors contributed equally to this work.

^|| To whom correspondence should be addressed: EMBL DESY, Notkestrasse 85, Bldg. 25A, D-22603 Hamburg, Germany. Tel.: 49-40-89902-126; Fax: 49-40-89902-149; E-mail: wilmanns{at}embl-hamburg.de.

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