The role of glutamine synthetase in the pathogenesis of Neisseria meningitidis

Neisseria meningitidisis a cause of meningitis and severe sepsis. A moonlighting protein is a protein with the ability to perform additional task(s) alongside its recognised function. These proteins have been identified in both prokaryotic and eukaryotic cells and they represent a highly conserved subset of proteins that typically are either metabolic pathway-associated enzymes or act as molecular chaperones. To explore the role of GlnA in the pathogenesis of meningococcal disease, the encoding gene designated NMB0359, was amplified from the wild-type meningococcal strain MC58 and cloned into the pQE-30 expression vector. Recombinant glutamine synthetase (rGlnA) was expressed in E. coli and purified by immobilised metal affinity chromatograph. Rabbit antisera was raised against purified rGlnA (RαGlnA) and used to investigate the localisation of GlnA at the cell surface. Attempts were also made to generate glnA knockout and complemented strains of wild-type N. meningitidis. rGlnA was successfully purified from E. coli cell lysates under native conditions. A highly immuno-reactive band of the expected size (52 kDa) was observed when rGlnA immunoblot was probed with RαGlnA. GlnA could be detected on the surface of wild-type encapsulated N. meningitidis MC58 using whole-cell enzyme linked immunosorbent assay (ELISA). Surface localisation of GlnA indicates that it may be a moonlighting protein carrying out function(s) at the cell surface. Future work will investigate possible moonlighting functions which may include adhesion to host cells and proteins, regulation of the host immune response, and contribution to bacterial virulence.