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Journal of Bacteriology, November 2008, p. 7431-7440, Vol. 190, No. 22
0021-9193/08/$08.00+0     doi:10.1128/JB.00652-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Outer and Inner Membrane Proteins Compose an Arginine-Agmatine Exchange System in Chlamydophila pneumoniae{triangledown} ,{dagger}

Conor B. Smith1 and David E. Graham2,3*

Microbiology Graduate Program, The University of Texas at Austin, Austin, Texas 78712,1 Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712,2 Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 787123

Received 9 May 2008/ Accepted 3 September 2008

Most chlamydial strains have a pyruvoyl-dependent decarboxylase protein that converts L-arginine to agmatine. However, chlamydiae do not produce arginine, so they must import it from their host. Chlamydophila pneumoniae has a gene cluster encoding a putative outer membrane porin (CPn1033 or aaxA), an arginine decarboxylase (CPn1032 or aaxB), and a putative cytoplasmic membrane transporter (CPn1031 or aaxC). The aaxC gene was expressed in Escherichia coli producing an integral cytoplasmic membrane protein that catalyzed the exchange of L-arginine for agmatine. Expression of the aaxA gene produced an outer membrane protein that enhanced the arginine uptake and decarboxylation activity of cells coexpressing aaxB and aaxC. This chlamydial arginine/agmatine exchange system complemented an E. coli mutant missing the native arginine-dependent acid resistance system. These cells survived extreme acid shock in the presence of L-arginine. Biochemical and evolutionary analysis showed the aaxABC genes evolved convergently with the enteric arginine degradation system, and they could have a different physiological role in chlamydial cells. The chlamydial system uniquely includes an outer membrane porin, and it is most active at a higher pH from 3 to 5. The chlamydial AaxC transporter was resistant to cadaverine, L-lysine and L-ornithine, which inhibit the E. coli AdiC antiporter.

* Corresponding author. Mailing address: Department of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station A5300, Austin, TX 78712. Phone: (512) 471-4491. Fax: (512) 471-8696. E-mail: degraham{at}mail.utexas.edu

{triangledown} Published ahead of print on 12 September 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, November 2008, p. 7431-7440, Vol. 190, No. 22
0021-9193/08/$08.00+0     doi:10.1128/JB.00652-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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