Effect of Factor H-Binding Protein Sequence Variation on Factor H Binding and Survival ofNeisseria meningitidisin Human Blood

Abstract

Binding of the complement inhibitor factor H (fH) to the surface of Neisseria meningitidis is critical for evasion of innate host defenses. The meningococcal vaccine candidate factor H-binding protein (fHbp) serves as an fH ligand. We prepared 16 recombinant fHbp natural sequence variants. By enzyme-linked immunosorbent assay (ELISA), the variants from a New Zealand epidemic strain (fHbp ID 14) and from an endemic United Kingdom strain (ID 15) showed 10-fold lower fH binding than a reference fHbp from an epidemic Norwegian strain (ID 1). By surface plasmon resonance, association rate constants (k a ) for fHbp ID 14 and 15 were similar to those for ID 1, but dissociation rate constants (k d ) were 4-to 10-fold higher than those for ID 1. To determine the effect of fH affinity on fHbp fitness, we prepared isogenic mutants of strain H44/76 that expressed fHbp ID 1, 14, or 15. By flow cytometry, mutants expressing fHbp ID 14 or 15 had lower fH binding than ID 1. When incubated in plasma or blood of nonimmune donors, all three mutants showed similar increases in CFU/ml. In contrast, an isogenic fHbp knockout mutant, which grew well in broth, was rapidly killed in plasma or blood. Thus, although fHbp expression was required for survival of strain H44/76 in blood or plasma, expression of two natural fHbp sequence variants with lower fH affinity had minimal or no effect on nonimmune clearance. One reason may be the high fH concentrations in normal serum, which favor saturation of fH binding to fHbp, even when dissociation rates varied over 10-fold.

Meningococcal Factor H Binding Protein Vaccine Antigens with Increased Thermal Stability and Decreased Binding of Human Factor H

“…3A), as we had observed previously (31). Based on the FH concentrations needed to obtain an optical density of 1.0 (Fig.…”

Defining a protective epitope on factor H binding protein, a key meningococcal virulence factor and vaccine antigen

“…Given this significant overlap, it is not surprising that the binding of fHbp to fH was inhibited by addition of mAb 12C1, although structural data show that Fab 12C1 is not a structural mimic of fH. Moreover, the affinity of fHbp to mAb 12C1 (K D < 0.05 nM) is remarkably higher than the affinity reported for fHbp to hfH (5-45 nM) (22,27,32,33), thus explaining the observed capacity of mAb 12C1 to displace fH from the fHbp:hfH complex. The crystal structure, together with multiple sequence alignments, also indicated a subset of fHbp residues potentially responsible for the var1 binding specificity of mAb 12C1.…”

Design of Meningococcal Factor H Binding Protein Mutant Vaccines That Do Not Bind Human Complement Factor H

“…4B and C), suggested that fH interactions were fundamentally different between the different fHbp variant groups. In previous studies, binding affinities of fH to fHbp also were reported to be higher for sequence variants in variant groups 2 and 3 than in variant group 1 (17,50), which also suggested that the fH-binding modes may be different between fHbp variants. Using a structural homology modeling approach, we identified 63 residues that potentially played a role in the interaction of fHbp with human fH.…”