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Open Access Research

The emerging periplasm-localized subclass of AroQ chorismate mutases, exemplified by those from Salmonella typhimurium and Pseudomonas aeruginosa

David H Calhoun1, Carol A Bonner2, Wei Gu2, Gary Xie23 and Roy A Jensen123*

Author affiliations

1 Department of Chemistry, City College of New York, New York, NY 10031, USA

2 Department of Microbiology and Cell Science, Gainesville, FL 32611, USA

3 BioScience Division, Los Alamos National Laboratory, Los Alamos, NM 87544, USA

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Citation and License

Genome Biology 2001, 2:research0030-research0030.16  doi:10.1186/gb-2001-2-8-research0030

Published: 27 July 2001

Abstract

Background

Chorismate mutases of the AroQ homology class are widespread in the Bacteria and the Archaea. Many of these exist as domains that are fused with other aromatic-pathway catalytic domains. Among the monofunctional AroQ proteins, that from Erwinia herbicola was previously shown to have a cleavable signal peptide and located in the periplasmic compartment. Whether or not this might be unique to E. herbicola was unknown.

Results

The gene coding for the AroQ protein was cloned from Salmonella typhimurium, and the AroQ protein purified from both S. typhimurium and Pseudomonas aeruginosa was shown to have a periplasmic location. The periplasmic chorismate mutases (denoted *AroQ) are shown to be a distinct subclass of AroQ, being about twice the size of cytoplasmic AroQ proteins. The increased size is due to a carboxy-terminal extension of unknown function. In addition, a so-far novel aromatic aminotransferase was shown to be present in the periplasm of P. aeruginosa.

Conclusions

Our analysis has detected a number of additional *aroQ genes. The joint presence of *AroQ, cyclohexadienyl dehydratase and aromatic aminotransferase in the periplasmic compartment of P. aeruginosa comprises a complete chorismate-to-phenylalanine pathway and accounts for the "hidden overflow pathway" to phenylalanine described previously.