title: Outer and inner membrane proteins compose an arginine-agmatine exchange system in Chlamydophila pneumoniae.
abstract: 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.
authors.affiliation: Department of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station A5300, Austin, TX 78712, USA.
authors.forename: Conor B
authors.initials: CB
authors.lastname: Smith
authors.forename: David E
authors.initials: DE
authors.lastname: Graham
mesh_terms: D000376:Agmatine / Q000378:metabolism*; D001120:Arginine / Q000378:metabolism*; D001426:Bacterial Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002262:Carboxy-Lyases / Q000235:genetics / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010802:Phylogeny; D021381:Protein Transport; D053719:Tandem Mass Spectrometry
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D000376:Agmatine; D001120:Arginine; D002262:Carboxy-Lyases; C019722:arginine decarboxylase
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