Analysis of the resistance-nodulation-division and HOP families of cell envelope proteins in helicobacter pylori

This study was initiated to identify potential genes that play a functional role in the in vivo antibiotic resistance of Helicobacter pylori. Translational fusions of H. pylori genes to alkaline phosphatase were made to identify genes whose products were secreted or exported in Escherichia coli. The initial screen identified three potential H. pylori efflux genes of the bacterial resistance-nodulation-division family. One of the efflux systems was found to be expressed only in vivo and I was not able to identify efflux activity in in vitro-grown H. pylori. The overall results of these experiments were consistent with the suggestion that these efflux systems do not function in the in vitro intrinsic resistance of H. pylori to antibiotics. A second line of investigation analyzed members of the H. pylori Hop family of outer membrane/adhesin proteins. Exner et al. (Infection & Immunity 63:1567-1572, 1995) previously described this family of 5 porin proteins based on extensive N-terminal amino acid similarity. This family was further expanded to include 32 proteins containing extensive C-terminal amino acid similarity by Tomb et al. (Nature 388:539-547, 1997). My analysis of the H. pylori genome has further expanded this family to 34 members. The DN A sequences encoding the conserved sequence motifs that are found within the Hop family had been proposed to function in homologous recombination to generate antigenic diversity or in response to environmental changes. However, my comparison of the sequences of the Hop family genes in two H. pylori strains suggested that the conserved sequences did not function in recombination. Based on molecular modeling of HopE, I proposed and tested, by linker insertion mutagenesis, the hypothesis that the conserved sequence motifs are part of a conserved structural motif. The overall results of these experiments supported the hypothesis that the conserved sequences encode a conserved structural motif for a family of β-barrel proteins.Science, Faculty ofMicrobiology and Immunology, Department ofGraduat