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J. Bacteriol. doi:10.1128/JB.01427-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

CapA, an autotransporter protein of Campylobacter jejuni, mediates association to human epithelial cells and colonization of the chicken gut

Molecular Bacteriology and Immunology Group, Institute of Infection, Immunity & Inflammation, School of Molecular Medical Sciences, Queen's Medical Centre, University of Nottingham, Nottingham NG7 2UH, UK; Institute for Animal Health, Compton, Berkshire RG20 7NN, UK

^* To whom correspondence should be addressed. Email: daa{at}nottingham.ac.uk.

	Abstract

Two putative autotransporter proteins, CapA and CapB, were identified in silico from the genome sequence of Campylobacter jejuni NCTC11168. The genes encoding each protein contain homopolymeric tracts, suggestive of phase variation mediated by a slipped-strand mispairing mechanism; in each case the gene sequence contained frame shifts at these positions. The C-terminal two-thirds of the two genes, as well as a portion of the predicted signal peptides, were identical; the remaining N-terminal portions were gene-specific. Both genes were cloned and expressed; recombinant polypeptides were purified and used to raise rabbit polyclonal mono-specific antisera. Using immunoblotting, expression of the ca.116 kDa CapA protein was demonstrated in in vitro-grown cells of strain NCTC11168, in four out of eleven recent human fecal isolates and in two out of eight sequence-typed strains examined. Expression of CapB was not detected in any of the strains tested. Surface localization of CapA was demonstrated by sub-cellular fractionation and immunogold electron microscopy. Export of CapA was inhibited by globomycin, reinforcing the bioinformatic prediction that the protein is a lipoprotein. A capA insertion mutant had a significantly reduced capacity for association and invasion of Caco-2 cells and failed to colonize and persist in chickens indicating that CapA plays a role in host association and colonization by Campylobacter. In view of this demonstrated role, we propose that CapA stands for Campylobacter adhesion protein A.

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