Role of Gonococcal Neisserial Surface Protein A (NspA) in Serum Resistance and Comparison of Its Factor H Binding Properties with Those of Its Meningococcal Counterpart

Abstract

Neisseria gonorrhoeae, the causative agent of gonorrhea, has evolved several mechanisms to subvert complement, including binding of the complement inhibitor factor H (FH). We previously reported FH binding to N. gonorrhoeae independently of lipooligosaccharide (LOS) sialylation. Here we report that factor H-like protein 1 (FHL-1), which contains FH domains 1 through 7 and possesses complement-inhibitory activity, also binds to N. gonorrhoeae. The ligand for both FH and FHL-1 was identified as neisserial surface protein A (NspA), which has previously been identified as a ligand for these molecules on Neisseria meningitidis. As with N. meningitidis NspA (Nm-NspA), N. gonorrhoeae NspA (Ng-NspA) bound FH/FHL-1 through FH domains 6 and 7. Binding of FH/FHL-1 to NspA was human specific; the histidine (H) at position 337 of domain 6 contributed to human-specific FH binding to both Ng- and Nm-NspA. FH/FHL-1 bound Nm-NspA better than Ng-NspA; introducing Q at position 73 (loop 2, present in Ng-NspA) or replacing V and D at positions 112 and 113 in Nm-NspA loop 3 with A and H (Ng-NspA), respectively, reduced FH/FHL-1 binding. The converse Ng-NspA to Nm-NspA mutations increased FH/FHL-1 binding. Binding of FH/FHL-1 through domains 6 and 7 to N. gonorrhoeae increased with truncation of the heptose I (HepI) chain of LOS and decreased with LOS sialylation. Loss of NspA significantly decreased serum resistance of N. gonorrhoeae with either wild-type or truncated LOS. This report highlights the role for NspA in enabling N. gonorrhoeae to subvert complement despite LOS phase variation. Knowledge of FH-NspA interactions will inform the design of vaccines and immunotherapies against the global threat of multidrug-resistant gonorrhea.

C4BP-IgM protein as a therapeutic approach to treat Neisseria gonorrhoeae infections

“…In addition, combination of the 2 C4BP-IgM and FH-IgG chimeric proteins may represent a rational strategy to target simultaneously a broad range of strains, which might be able to bind either C4BP or FH or both proteins. C4BP-IgM targets PorB, FH domains 18-20 fused to IgG Fc bind sialylated LOS and PorB (39,40), and FH domains 6 and 7 fused to Fc target gonococcal NspA (41). Combination treatment directed against distinct molecules that serve important immune evasion functions (complement inhibition) or are essential for gonococcal viability (e.g., PorB) will make the development of resistance unlikely.…”

Progress Toward a Gonococcal Vaccine: The Way Forward

“…It is important to note that PorB binding is specific for human C4BP and factor H, so these effects may not be evident in serum bactericidal assays if non-human complement is used or in most animal infection models. Gonococcal NspA (neisserial surface protein A) also binds human factor H (73), but the gonococcal homolog of the meningococcal factor H-binding protein lacks a signal peptide and therefore is not available on the cell surface to bind factor H (74).…”

<p>Chimeric hepatitis B virus core particles displaying Neisserial surface protein A confer protection against virulent <em>Neisseria meningitidis</em> serogroup B in BALB/c mice</p>

“…NspA is a highly immunogenic antigen against all pathogenic Neisserial serogroups in mice, and there is evidence that it belongs to the OPa protein family, which mediates cell adhesion. In a mouse model, NspA induced a protective immune response against serogroups A, B, and C 8. Published data showed that NspA can readily access the surface of the cell to evoke complement-mediated bactericidal activity via anti-NspA mAbs.…”