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J. Biol. Chem., Vol. 280, Issue 19, 18568-18572, May 13, 2005

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Complex Formation between Glutamyl-tRNA Reductase and Glutamate-1-semialdehyde 2,1-Aminomutase in Escherichia coli during the Initial Reactions of Porphyrin Biosynthesis^*

Corinna Lüer, Stefan Schauer, Kalle Möbius, Jörg Schulze¶, Wolf-Dieter Schubert¶, Dirk W. Heinz¶, Dieter Jahn, and Jürgen Moser||

From the Institute of Microbiology, Technical University Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany, Institute for Molecular Biology and Biophysics, Swiss Federal Institute of Technology, Schafmattstrasse 20, CH-8093 Zürich, Switzerland, and ^¶Division of Structural Biology, German Research Center for Biotechnology, Mascheroder Weg 1, D-38124 Braunschweig, Germany

In Escherichia coli the first common precursor of all tetrapyrroles, 5-aminolevulinic acid, is synthesized from glutamyl-tRNA (Glu-tRNA^Glu) in a two-step reaction catalyzed by glutamyl-tRNA reductase (GluTR) and glutamate-1-semialdehyde 2,1-aminomutase (GSA-AM). To protect the highly reactive reaction intermediate glutamate-1-semialdehyde (GSA), a tight complex between these two enzymes was proposed based on their solved crystal structures. The existence of this hypothetical complex was verified by two independent biochemical techniques. Co-immunoprecipitation experiments using antibodies directed against E. coli GluTR and GSA-AM demonstrated the physical interaction of both enzymes in E. coli cell-free extracts and between the recombinant purified enzymes. Additionally, the formation of a GluTR·GSA-AM complex was identified by gel permeation chromatography. Complex formation was found independent of Glu-tRNA^Glu and cofactors. The analysis of a GluTR mutant truncated in the 80-amino acid C-terminal dimerization domain (GluTR-A338Stop) revealed the importance of GluTR dimerization for complex formation. The in silico model of the E. coli GluTR·GSA-AM complex suggested direct metabolic channeling between both enzymes to protect the reactive aldehyde species GSA. In accordance with this proposal, side product formation catalyzed by GluTR was observed via high performance liquid chromatography analysis in the absence of the GluTR·GSA-AM complex.

Received for publication, January 13, 2005 , and in revised form, March 4, 2005.

^* This work was supported by grants from the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie (to D. W. H. and D. J.). 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. Tel.: 49-531-391-5808; Fax: 49-531-391-5854; E-mail: j.moser{at}tu-bs.de.

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