NHBA is processed by kallikrein from human saliva

Neisserial Heparin Binding Antigen (NHBA) is a surface-exposed lipoprotein and a component of the Bexsero vaccine. NHBA is characterized by the presence of a highly conserved Arg-rich region involved in binding to heparin and heparin sulphate proteoglycans present on the surface of host epithelial cells, suggesting a possible role of NHBA during N. meningitidis colonization. NHBA has been shown to be cleaved by the bacterial NalP protein, a meningococcal protease and by human lactoferrin (hLF), a host protease present in different body fluids (saliva, breast milk and serum). Cleavage occurs upstream or downstream the Arg-rich region. Since the human nasopharynx is the only known reservoir of infection, we further investigated the susceptibility of NHBA to human proteases present in the saliva to assess whether proteolytic cleavage could happen during the initial steps of colonization. Here we show that human saliva proteolytically cleaves NHBA; and identified human kallikrein 1 (KLK1) as the main protease responsible for this cleavage. Kallikrein is an important enzyme present in blood plasma, lymph, urine, saliva, pancreatic juices, and other body fluids that catalyze the proteolysis of several human proteins. We report the in vitro characterization of NHBA cleavage by kallikrein; the identification of the cleavage in the recombinant NHBA protein and, on the native protein, when expressed on live bacteria. Overall, this findings provide new insights on NHBA as target of host proteases, highlights a potential role of NHBA in the Neisseria meningitidis nasopharyngeal colonization, and of kallikrein as a defensive agent against meningococcal infection.