Dissecting the role of Neisseria Heparin Binding Antigen cleavage during adaptation of Neisseria meningitidis to mucosal surface

Neisserial Heparin Binding Antigen (NHBA) is a surface-exposed lipoprotein specific for Neisseria and is one of the three main protein antigens of the Bexsero vaccine. Meningococcal and human proteases, including lactoferrin and kallikrein, cleave NHBA protein upstream or downstream a conserved Arg-rich motif, respectively. The cleavage results in the release of the C-terminal portion of the protein. C-terminal fragment originating from the processing of meningococcal proteases, referred as C2 fragment, exerts a toxic effect on endothelial cells altering their permeability. In this work, we reported that recombinant C2 fragment has no influence on the integrity of human airway epithelial cell monolayers, consistently with previous findings showing that N. meningitidis traverses the epithelial barrier without disrupting the junctional structures. Unexpectedly, epithelial cells constantly secreted proteases responsible for a rapid processing of C2 fragment, generating a new fragment that does not contain the Arg-rich motif. This cleavage might inactivate the toxic effect of C2 fragment by eliminating its docking domain. Epithelial cell proteases processed also the NHBA full-length protein, and we demonstrated it on live bacteria. Moreover, looking for the epithelial cell protease responsible for this processing, we identified the C3-convertase of alternative complement pathway as a novel human protease able to cleave NHBA during meningococcal infection. Overall, our data provide new insights on the cleavage of NHBA protein during meningococcal infection. This cleavage occurs at different stages of the infection, and it likely has a different role depending on the environment the bacterium is interacting with.