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Journal of Bacteriology, July 2008, p. 5044-5056, Vol. 190, No. 14
0021-9193/08/$08.00+0     doi:10.1128/JB.00224-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Type II Secretory Pathway for Surface Secretion of DraD Invasin from the Uropathogenic Escherichia coli Dr⁺ Strain

Beata Zalewska-Pitek,^1* Katarzyna Bury,¹ Rafa Pitek,¹ Piotr Brudziak,² and Józef Kur¹

Department of Microbiology, Gdask University of Technology, ul. G. Narutowicza 11/12, 80-952 Gdask, Poland,¹ Department of Physical Chemistry, Gdask University of Technology, ul. G. Narutowicza 11/12, 80-952 Gdask, Poland²

Received 13 February 2008/ Accepted 9 May 2008

The virulence of the uropathogenic Escherichia coli Dr⁺ IH11128 strain is associated with the presence of Dr fimbrial structures and a DraD invasin which can act as a fimbrial capping domain at the bacterial cell surface. However, a recent study suggests that the DraD protein is surface exposed in two forms: fimbria associated and fimbria nonassociated (prone to interaction with the N-terminal extension of the DraE protein located on the fimbrial tip). The actual mechanism of DraD surface secretion is presently unknown. We identified a previously unrecognized type II secretory pathway (secreton) in the uropathogenic E. coli Dr⁺ strain which is well conserved among gram-negative bacteria and used mainly for secretion of virulence determinants. An active secreton is composed of 12 to 15 different proteins, among which GspD functions as an outer-membrane channel to permit extrusion of proteins in a folded state. Therefore, we inactivated the pathway by inserting the group II intron into a gspD gene of the type II secretion machinery by site-specific recombination. DraD secretion by the E. coli Dr⁺ and gspD mutant strains was determined by immunofluorescence microscopy (with antibodies raised against DraD) and an assay of cell binding between bacteria and HeLa cells. The specificity of DraD-mediated bacterial binding for the integrin receptor was confirmed by examination of the adhesion of DraD-coated beads to HeLa cells in the presence and absence of ₅β₁ monoclonal antibodies. The investigations that we performed showed that type II secretion in E. coli Dr⁺ strains leads to DraD translocation at the bacterial cell surfaces.

Published ahead of print on 23 May 2008.