Evidence for Conserved Function of γ–Glutamyltranspeptidase in Helicobacter Genus

Abstract

The confounding consequences of Helicobacter bilis infection in experimental mice populations are well recognized, but the role of this bacterium in human diseases is less known. Limited data are available on virulence determinants of this species. In Helicobacter pylori, γ-glutamyltranspeptidase (γGT) contributes to the colonization of the gastric mucosa and to the pathogenesis of peptic ulcer. The role of γGT in H. bilis infections remains unknown. The annotated genome sequence of H. bilis revealed two putative ggt genes and our aim was to characterize these H. bilis γGT paralogues. We performed a phylogenetic analysis to understand the evolution of Helicobacter γGTs and to predict functional activities of these two genes. In addition, both copies of H. bilis γGTs were expressed as recombinant proteins and their biochemical characteristics were analysed. Functional complementation of Esherichia coli deficient in γGT activity and deletion of γGT in H. bilis were performed. Finally, the inhibitory effect of T-cell and gastric cell proliferation by H. bilis γGT was assessed. Our results indicated that one gene is responsible for γGT activity, while the other showed no γGT activity due to lack of autoprocessing. Although both H. bilis and H. pylori γGTs exhibited a similar affinity to L-Glutamine and γ-Glutamyl-p-nitroanilide, the H. bilis γGT was significantly less active. Nevertheless, H. bilis γGT inhibited T-cell proliferation at a similar level to that observed for H. pylori. Finally, we showed a similar suppressive influence of both H. bilis and H. pylori γGTs on AGS cell proliferation mediated by an apoptosis-independent mechanism. Our data suggest a conserved function of γGT in the Helicobacter genus. Since γGT is present only in a few enterohepatic Helicobacter species, its expression appears not to be essential for colonization of the lower gastrointestinal tract, but it could provide metabolic advantages in colonization capability of different niches.

Helicobacter saguini, a Novel Helicobacter Isolated from Cotton-Top Tamarins with Ulcerative Colitis, Has Proinflammatory Properties and Induces Typhlocolitis and Dysplasia in Gnotobiotic IL-10 −/− Mice

“…Importantly, H. saguini is sufficient by itself to cause IBD in monoassociated IL-10 Ϫ/Ϫ mice, unlike H. hepaticus (41,42), suggesting that the expression of virulence properties of H. saguini does not require cocolonization of the lower bowel with other flora to initiate an inflammatory response. (43)(44)(45)(46). Also, in vitro data show that GGT inhibits gastrointestinal and lymphocyte cell proliferation as well as having a role in producing reactive free oxygen species (43)(44)(45)(46).…”

“…(43)(44)(45)(46). Also, in vitro data show that GGT inhibits gastrointestinal and lymphocyte cell proliferation as well as having a role in producing reactive free oxygen species (43)(44)(45)(46). NF-B activation and IL-8 secretion in gastrointestinal cell lines may have also been stimulated by GGT expression.…”

Helicobacter spp. Other than H. pylori

“…Rossi et al [23] functionally analyzed both of H. bilis ggt paralogues, named bgh1 (H. bilis ggt homologue 1) and bgh2 (H. bilis ggt homologue 2). The authors observed that only Bgh2 was responsible for cGT activity, while Bgh1 showed no activity because of lack of autoprocessing.…”

“…The authors further identified H. suis cGT (HscGT) and H. pylori cGT (HpcGT) as the major factors involved in both apoptotic and necrotic death of AGS cells through an extracellular increase in the oxidative stress burden, leading to lipid peroxidation. A conserved function of cGT in the Helicobacter genus was hypothesised by Rossi et al [23] studying the biochemical and biological properties of H. bilis cGT (HbcGT). The authors observed that HbcGT inhibits T-cell (Jurkat) proliferation to a similar level as that observed for HpcGT, confirming the potential immunosuppressive role of secreted Helicobacter cGTs.…”

Helicobacter pylori γ-Glutamyltranspeptidase Induces Tolerogenic Human Dendritic Cells by Activation of Glutamate Receptors

“…pylori gGT is a bacterial enzyme highly conserved among strains and important for colonization in vivo (7,8). gGT catalyzes the hydrolysis and transpeptidation of g-glutamyl compounds such as oxidized and reduced glutathione (9).…”