GNA33 from Neisseria meningitidis serogroup B encodes a membrane-bound lytic transglycosylase (MltA)

In a previous study, we used the genome of serogroup B Meningococcus to identify novel vaccine candidates. One of these molecules, GNA33, is well conserved among Meningococcus B strains, other Meningococcus serogroups and Gonococcus and induces bactericidal antibodies as a result of being a mimetic antigen of the PorA epitope P1.2. GNA33 encodes a 48-kDa lipoprotein that is 34.5% identical with membrane-bound lytic transglycosylase A (MltA) from Escherichia coli. In this study, we expressed GNA33, i.e. Meningococcus MltA, as a lipoprotein in E. coli. The lipoprotein nature of recombinant MltA was demonstrated by incorporation of [H-3]palmitate. MltA lipoprotein was purified to homogeneity from E. coli membranes by cation-exchange chromatography. Muramidase activity was confirmed when MltA was shown to degrade insoluble murein sacculi and unsubstituted glycan strands. HPLC analysis demonstrated the formation of 1,6-anhydrodisaccharide tripeptide and tetrapeptide reaction products, confirming that the protein is a lytic transglycosylase. Optimal muramidase activity was observed at pH 5.5 and 37 degreesC and enhanced by Mg2+, Mn2+ and Ca2+. The addition of Ni2+ and EDTA had no significant effect on activity, whereas Zn2+ inhibited activity. Triton X100 stimulated activity 5.1-fold. Affinity chromatography indicated that MltA interacts with penicillin-binding protein 2 from Meningococcus B, and, like MltA from E. coli, may form part of a multienzyme complex.