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Journal of Bacteriology, May 2002, p. 2709-2718, Vol. 184, No. 10
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.10.2709-2718.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Caulobacter crescentus Synthesizes an S-Layer-Editing Metalloprotease Possessing a Domain Sharing Sequence Similarity with Its Paracrystalline S-Layer Protein

Elizabeth Umelo-Njaka,1 Wade H. Bingle,1 Faten Borchani,1 Khai D. Le,1 Peter Awram,2 Theo Blake,1 John F. Nomellini,1 and John Smit1*

Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada,1 School of Biological Sciences, University of Auckland, Auckland, New Zealand2

Received 3 October 2001/ Accepted 22 February 2002

Strains of Caulobacter crescentus elaborate an S-layer, a two-dimensional protein latticework which covers the cell surface. The S-layer protein (RsaA) is secreted by a type I mechanism (relying on a C-terminal signal) and is unusual among type I secreted proteins because high levels of protein are produced continuously. In efforts to adapt the S-layer for display of foreign peptides and proteins, we noted a proteolytic activity that affected S-layer monomers with foreign inserts. The cleavage was precise, resulting in fragments with an unambiguous N-terminal sequence. We developed an assay to screen for loss of this activity (i.e., presentation of foreign peptides without degradation), using transposon and traditional mutagenesis. A metalloprotease gene designated sap (S-layer-associated protease) was identified which could complement the protease-negative mutants. The N-terminal half of Sap possessed significant similarity to other type I secreted proteases (e.g., alkaline protease of Pseudomonas aeruginosa), including the characteristic RTX repeat sequences, but the C-terminal half which normally includes the type I secretion signal exhibited no such similarity. Instead, there was a region of significant similarity to the N-terminal region of RsaA. We hypothesize that Sap evolved by combining the catalytic portion of a type I secreted protease with an S-layer-like protein, perhaps to associate with nascent S-layer monomers to "scan" for modifications.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada. Phone: (604) 822-4417. Fax: (604) 822-6041. E-mail: jsmit{at}interchange.ubc.ca.

Journal of Bacteriology, May 2002, p. 2709-2718, Vol. 184, No. 10
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.10.2709-2718.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Smit, J., Kaltashov, I. A., Cotter, R. J., Vinogradov, E., Perry, M. B., Haider, H., Qureshi, N. (2008). Structure of a novel lipid A obtained from the lipopolysaccharide of Caulobacter crescentus. Innate Immunity 14: 25-36 [Abstract]  
  • Nomellini, J. F., Duncan, G., Dorocicz, I. R., Smit, J. (2007). S-Layer-Mediated Display of the Immunoglobulin G-Binding Domain of Streptococcal Protein G on the Surface of Caulobacter crescentus: Development of an Immunoactive Reagent. Appl. Environ. Microbiol. 73: 3245-3253 [Abstract] [Full Text]  
  • Ford, M. J., Nomellini, J. F., Smit, J. (2007). S-Layer Anchoring and Localization of an S-Layer-Associated Protease in Caulobacter crescentus. J. Bacteriol. 189: 2226-2237 [Abstract] [Full Text]  
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