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Infection and Immunity, October 1999, p. 5386-5394, Vol. 67, No. 10
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Functional Characterization of a Serine/Threonine Protein Kinase of Pseudomonas aeruginosa

S. Timothy Motley and Stephen Lory*

Department of Microbiology, University of Washington School of Medicine, Seattle, Washington 98195

Received 17 March 1999/Returned for modification 7 May 1999/Accepted 21 July 1999

Protein kinases play a key role in signal transduction pathways in both eukaryotic and prokaryotic cells. Using in vivo expression technology, we have identified several promoters in Pseudomonas aeruginosa which are preferentially activated during infection of neutropenic mice. One of these promoters directs the transcription of a gene encoding a putative protein kinase similar to the enzymes found in eukaryotic cells. The full characterization of this protein, termed PpkA, is presented in this communication. The ppkA gene encodes a 1,032-amino-acid polypeptide with an N-terminal catalytic domain showing all of the conserved residues of protein kinases with the substrate phosphorylation specificities for serine and threonine residues. The catalytic domain is linked to the rest of the protein by a short proline-rich segment. The enzymes showed anomalous migration behavior when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which could be attributed to autophosphorylation activity. The full-length enzyme was expressed as an oligohistidine fusion protein and was shown to phosphorylate several artificial protein substrates. Both autophosphorylation and phosphorylation of added substrates were strongly reduced by a single-amino-acid substitution in the catalytic domain of PpkA. Although PpkA appears to be differentially phosphorylated by autocatalysis, the levels of phosphorylation have minimal effect on its overall enzymatic activity. Our results, therefore, indicate the operation of a novel protein phosphorylation mechanism during transduction of signals in P. aeruginosa, and this pathway may be important in regulating the expression of virulence factors by this pathogen during certain phases of infection.

* Corresponding author. Mailing address: Department of Microbiology, University of Washington, Box 357242, Seattle, WA 98195. Phone: (206) 543-1444. Fax: (206) 543-8297. E-mail: guidos{at}u.washington.edu.

Infection and Immunity, October 1999, p. 5386-5394, Vol. 67, No. 10
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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Copyright © 1999 by the American Society for Microbiology. All rights reserved.