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Infection and Immunity, January 2005, p. 135-145, Vol. 73, No. 1
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.1.135-145.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Molecular Aspects of Biogenesis of Escherichia coli Dr Fimbriae: Characterization of DraB-DraE Complexes

Rafa Pitek,¹ Beata Zalewska,¹ Olga Kolaj,¹ Micha Ferens,¹ Bogdan Nowicki,^2,3 and Józef Kur^1*

Department of Microbiology, Gdask University of Technology, Gdask, Poland,¹ Department of Obstetrics and Gynecology,² Department of Microbiology and Immunology, The University of Texas Medical Branch, Galveston, Texas³

Received 30 April 2004/ Returned for modification 17 August 2004/ Accepted 20 September 2004

The Dr hemagglutinin of uropathogenic Escherichia coli is a fimbrial homopolymer of DraE subunits encoded by the dra operon. The dra operon includes the draB and draC genes, whose products exhibit homology to chaperone-usher proteins involved in the biogenesis of surface-located polymeric structures. DraB is one of the periplasmic proteins belonging to the superfamily of PapD-like chaperones. It possesses two conserved cysteine residues characteristic of the FGL subfamily of Caf1M-like chaperones. In this study we obtained evidence that DraB cysteines form a disulfide bond in a mature chaperone and have the crucial function of forming the DraB-DraE binary complex. Expression experiments showed that the DraB protein is indispensable in the folding of the DraE subunit to a form capable of polymerization. Accumulation of DraB-DraE_n oligomers, composed of head-to-tail subunits and the chaperone DraB, was observed in the periplasm of a recombinant E. coli strain which expressed DraB and DraE (but not DraC). To investigate the donor strand exchange mechanism during the formation of DraE oligomers, we constructed a series of DraE N-terminal deletion mutants. Deletion of the first three N-terminal residues of a potential donor strand resulted in a DraE protein lacking an oligomerization function. In vitro data showed that the DraE disulfide bond was not needed to form a binary complex with the DraB chaperone but was essential in the polymerization process. Our data suggest that assembly of Dr fimbriae requires a chaperone-usher pathway and the donor strand exchange mechanism.

Editor: V. J. DiRita

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