CAGL, A SPECIALIZED HELICOBACTER PYLORI ADHESIN, AS A POTENTIAL PHARMACOLOGICAL TARGET AND CANDIDATE FOR DEVELOPING NEW VACCINE

CagL is recognized as a specialized adhesin localized on the pilus surface of H. pyloriType IV secretion system (T4SS). CagL binds to α5β1 integrin on gastric epithelial cells by the RGD motif. This interaction contributes in triggering the virulence factor CagA delivery into target cells. Chronic gastritis, peptic ulcers and even cancer may represent the final effect after infection. However, the CagL-integrin interaction is not essential for the CagA translocation suggesting the existence of an alternative mechanism of action of CagL in H. pylori infection. Sequence analyses of CagL showed the presence of three motifs that resemble conserved motifs in ADP-ribosylating toxins. These motifs are involved in ADP-ribosylation activity which is one of the main mechanisms of cell intoxication employed by bacteria. A comparison between the aminoacidic sequences ofH. pylori strains available in databases showed that only Shi470 possesses an R in the first domain that could confer the expected ADP-ribosylation activity to the protein. R, in this region, is reported to be important for the nicotinamide adenine dinucleotide (NAD) binding. R is substituted by either N or S in other H. pylori strains. Thus, the attention has been focused on the pathogenic H. pylori Shi470 strain. Here, we cloned and purified recombinant CagL lacking the leader sequence, with the aim of investigating its biochemical properties. Preliminary results showed an auto-ADP ribosylation activity of CagL utilizing biotinylated NAD as substrate and chemiluminescence for activity detection. Moreover, CagL resulted sensitive to novobiocin, a potent ADP-ribosylation inhibitor, in a concentration dependent manner. Heat inactivation also inhibited the activity, thus confirming the absence of unspecific binding of substrate. We also demonstrated the protective efficacy in the murine model of infection of recombinant CagL which can be taken into consideration as antigen in therapeutic or preventive vaccines.