Mapping of theNeisseria meningitidisNadA Cell-Binding Site: Relevance of Predicted α-Helices in the NH₂-Terminal and Dimeric Coiled-Coil Regions

Abstract

NadA is a trimeric autotransporter protein of Neisseria meningitidis belonging to the group of oligomeric coiled-coil adhesins. It is implicated in the colonization of the human upper respiratory tract by hypervirulent serogroup B N. meningitidis strains and is part of a multiantigen anti-serogroup B vaccine. Structure prediction indicates that NadA is made by a COOH-terminal membrane anchor (also necessary for autotranslocation to the bacterial surface), an intermediate elongated coiled-coil-rich stalk, and an NH 2 -terminal region involved in cell interaction. Electron microscopy analysis and structure prediction suggest that the apical region of NadA forms a compact and globular domain. Deletion studies proved that the NH 2 -terminal sequence (residues 24 to 87) is necessary for cell adhesion. In this study, to better define the NadA cell binding site, we exploited (i) a panel of NadA mutants lacking sequences along the coiled-coil stalk and (ii) several oligoclonal rabbit antibodies, and their relative Fab fragments, directed to linear epitopes distributed along the NadA ectodomain. We identified two critical regions for the NadA-cell receptor interaction with Chang cells: the NH 2 globular head domain and the NH 2 dimeric intrachain coiled-coil ␣-helices stemming from the stalk. This raises the importance of different modules within the predicted NadA structure. The identification of linear epitopes involved in receptor binding that are able to induce interfering antibodies reinforces the importance of NadA as a vaccine antigen.

Phase Variation Mediates Reductions in Expression of Surface Proteins during Persistent Meningococcal Carriage

“…1A; see Table SA2 in the supplemental material). Since this gene encodes an adhesin (33,34), our results suggest that NadA is only required for initial colonization and is rapidly subject to selection for loss of expression as N. meningitidis persists in a host. Similar requirements during colonization may be ascribed to Opc and MspA, which encode known and putative adhesins (35,36) and were also found mainly in low expression states (52% for Opc and 78% for MspA; see Table SA6 in the supplemental material).…”

Structure of the meningococcal vaccine antigen NadA and epitope mapping of a bactericidal antibody

“…This adhesive activity has been mapped, at least partially, to an N-terminal region extending to residue T132 (23,24). Recently, interactions of NadA3 with β-1 integrin (25) and with the heat shock protein Hsp90 (26) have been reported.…”

New findings on the function and potential applications of the trimeric autotransporter adhesin

“…The Hap autotransporter from H. influenzae was found to be immunogenic in mice and can protect against diseases caused by non-typeable H. influenza . Two groups have shown experimental evidence that NhhA can induce bactericidal antibodies that can protect mice against meningococci (Weynants et al 2007;Tavano et al 2011). UspA1 and NadA induce antibody production in natural hosts and prevents the binding of M. catarrhalis to the cell receptor CEACAM1, decreasing the odds of infection (Hill et al 2005 (Raghunathan et al 2011).…”