Factor H Binding and Function in Sialylated Pathogenic Neisseriae is Influenced by Gonococcal, but Not Meningococcal, Porin

Abstract

Neisseria gonorrhoeae and Neisseria meningitidis both express the lacto-N-neotetraose (LNT) lipooligosaccharide (LOS) molecule that can be sialylated. Although gonococcal LNT LOS sialylation enhances binding of the alternative pathway complement inhibitor factor H and renders otherwise serum-sensitive bacteria resistant to complement-dependent killing, the role of LOS sialylation in meningococcal serum resistance is less clear. We show that only gonococcal, but not meningococcal, LNT LOS sialylation enhanced factor H binding. Replacing the porin (Por) B molecule of a meningococcal strain (LOS sialylated) that did not bind factor H with gonococcal Por1B augmented factor H binding. Capsule expression did not alter factor H binding to meningococci that express gonococcal Por. Conversely, replacing gonococcal Por1B with meningococcal PorB abrogated factor H binding despite LNT LOS sialylation. Gonococcal Por1B introduced in the background of an unsialylated meningococcus itself bound small amounts of factor H, suggesting a direct factor H-Por1B interaction. Factor H binding to unsialylated meningococci transfected with gonococcal Por1B was similar to the sialylated counterpart only in the presence of higher (20 μg/ml) concentrations of factor H and decreased in a dose-responsive manner by ∼80% at 1.25 μg/ml. Factor H binding to the sialylated strain remained unchanged over this factor H concentration range however, suggesting that LOS sialylation facilitated optimal factor H-Por1B interactions. The functional counterpart of factor H binding showed that sialylated meningococcal mutants that possessed gonococcal Por1B were resistant to complement-mediated killing by normal human serum. Our data highlight the different mechanisms used by these two related species to evade complement.

Sialic acid utilization by bacterial pathogens

“…Interestingly, the positive effect of LPS sialylation on fH binding requires the presence of the gonococcal porin PorB (Fig. 1), suggesting that sialylated LPS and PorB might constitute a composite epitope, or that sialylation might cause a conformational change in the LPS that unmasks novel sites in PorB (Madico et al, 2007). In NTHi, LPS sialylation inhibits deposition of C3 without entailing fH binding ( Fig.…”

“…To date it is not known whether the sialylated LPS is an actual binding site for fH (Fig. 1) (Madico et al, 2007). Interestingly, the positive effect of LPS sialylation on fH binding requires the presence of the gonococcal porin PorB (Fig.…”

Human Factor H Interacts Selectively with Neisseria gonorrhoeae and Results in Species-Specific Complement Evasion

“…The nonsialylated (control) strain F62 was killed Ͼ99% (0 -1% survival) by serum from every species tested including human (data not shown). The increase in HufH binding that occurs with sialylation of gonococcal LNT LOS is dependent on the inherent specificity of gonococcal Por (45). Having shown, however, that sialylation of Por1B strain F62 conferred resistance to chimpanzee serum in the absence of direct binding of ChfH to gonococci (Fig.…”

“…Affinity-isolated goat polyclonal Ab against HufH was made by Bethyl Laboratories using purified HufH (Complement Technology) as an immunogen (45). Goat anti-HufH was used in Western blotting experiments to detect free fH previously bound to gonococci during incubations and liberated during electrophoresis (see below).…”

A novel factor H-FC chimeric immunotherapeutic molecule against Neisseria gonorrhoeae

“…Sialylation of the LNT LOS structure enhances binding of the C-terminal domains 18-20 of human FH to gonococci (23,24). This increase in FH binding is dependent on expression of gonococcal porin (PorB); replacing gonococcal PorB with meningococcal PorB abrogates Neu5Ac-mediated enhancement of FH binding (25). Several strains of N. gonorrhoeae also bind FH independently of LOS sialylation (26).…”