cag , a pathogenicity island of Helicobacter pylori, encodes type I-specific and disease-associated virulence factors

Abstract

cagA , a gene that codes for an immunodominant antigen, is present only in Helicobacter pylori strains that are associated with severe forms of gastroduodenal disease (type I strains). We found that the genetic locus that contains cagA ( cag ) is part of a 40-kb DNA insertion that likely was acquired horizontally and integrated into the chromosomal glutamate racemase gene. This pathogenicity island is flanked by direct repeats of 31 bp. In some strains, cag is split into a right segment ( cag I) and a left segment ( cag II) by a novel insertion sequence (IS 605 ). In a minority of H. pylori strains, cag I and cag II are separated by an intervening chromosomal sequence. Nucleotide sequencing of the 23,508 base pairs that form the cag I region and the extreme 3′ end of the cag II region reveals the presence of 19 ORFs that code for proteins predicted to be mostly membrane associated with one gene ( cagE ), which is similar to the toxin-secretion gene of Bordetella pertussis, ptlC, and the transport systems required for plasmid transfer, including the virB4 gene of Agrobacterium tumefaciens . Transposon inactivation of several of the cag I genes abolishes induction of IL-8 expression in gastric epithelial cell lines. Thus, we believe the cag region may encode a novel H. pylori secretion system for the export of virulence determinants.