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Journal of Bacteriology, January 2003, p. 80-88, Vol. 185, No. 1
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.1.80-88.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

The SecB Chaperone Is Bifunctional in Serratia marcescens: SecB Is Involved in the Sec Pathway and Required for HasA Secretion by the ABC Transporter

Guillaume Sapriel, Cécile Wandersman, and Philippe Delepelaire*

Unité des Membranes Bactériennes, URA CNRS 2172, Institut Pasteur, 75724 Paris Cedex 15, France

Received 18 July 2002/ Accepted 8 October 2002

HasA is the secreted hemophore of the heme acquisition system (Has) of Serratia marcescens. It is secreted by a specific ABC transporter apparatus composed of three proteins: HasD, an inner membrane ABC protein; HasE, another inner membrane protein; and HasF, a TolC homolog. Except for HasF, the structural genes of the Has system are encoded by an iron-regulated operon. In previous studies, this secretion system has been reconstituted in Escherichia coli, where it requires the presence of the SecB chaperone, the Sec pathway-dedicated chaperone. We cloned and inactivated the secB gene from S. marcescens. We show that S. marcescens SecB is 93% identical to E. coli SecB and complements the secretion defects of a secB mutant of E. coli for both the Sec and ABC pathways of HasA secretion. In S. marcescens, SecB inactivation affects translocation by the Sec pathway and abolishes HasA secretion. This demonstrates that S. marcescens SecB is the genuine chaperone for HasA secretion in S. marcescens. These results also demonstrate that S. marcescens SecB is bifunctional, as it is involved in two separate secretion pathways. We investigated the effects of secB point mutations in the reconstituted HasA secretion pathway by comparing the translocation of a Sec substrate in various mutants. Two different patterns of SecB residue effects were observed, suggesting that SecB functions may differ for the Sec and ABC pathways.

* Corresponding author. Mailing address: Unité des Membranes Bactériennes, URA CNRS 2172, Institut Pasteur, 25-28 rue du Dr. Roux, 75724 Paris Cedex 15, France. Phone: 33 1 40 61 32 76. Fax: 33 1 45 68 87 90. E-mail: pdelep{at}pasteur.fr.

Journal of Bacteriology, January 2003, p. 80-88, Vol. 185, No. 1
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.1.80-88.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Petty, N. K., Foulds, I. J., Pradel, E., Ewbank, J. J., Salmond, G. P. C. (2006). A generalized transducing phage ({phi}IF3) for the genomically sequenced Serratia marcescens strain Db11: a tool for functional genomics of an opportunistic human pathogen. Microbiology 152: 1701-1708 [Abstract] [Full Text]  
  • Wolff, N., Sapriel, G., Bodenreider, C., Chaffotte, A., Delepelaire, P. (2003). Antifolding Activity of the SecB Chaperone Is Essential for Secretion of HasA, a Quickly Folding ABC Pathway Substrate. J. Biol. Chem. 278: 38247-38253 [Abstract] [Full Text]  


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