Functional Comparison of the Binding of Factor H Short Consensus Repeat 6 (SCR 6) to Factor H Binding Protein fromNeisseria meningitidisand the Binding of Factor H SCR 18 to 20 toNeisseria gonorrhoeaePorin

Abstract

Both Neisseria meningitidis and Neisseria gonorrhoeae recruit the alternative pathway complement inhibitory protein factor H (fH) to their surfaces to evade complement-dependent killing. Meningococci bind fH via fH binding protein (fHbp), a surface-exposed lipoprotein that is subdivided into three variant families based on one classification scheme. Chimeric proteins that comprise contiguous domains of fH fused to murine Fc were used to localize the binding site for all three fHbp variants on fH to short consensus repeat 6 (SCR 6). As expected, fH-like protein 1 (FHL-1), which contains fH SCR 6, also bound to fHbp-expressing meningococci. Using site-directed mutagenesis, we identified histidine 337 and histidine 371 in SCR 6 as important for binding to fHbp. These findings may provide the molecular basis for recent observations that demonstrated human-specific fH binding to meningococci. Differences in the interactions of fHbp variants with SCR 6 were evident. Gonococci bind fH via their porin (Por) molecules (PorB.1A or PorB.1B); sialylation of lipooligosaccharide enhances fH binding. Both sialylated PorB.1B-and (unsialylated) PorB.1A-bearing gonococci bind fH through SCR 18 to 20; PorB.1A can also bind SCR 6, but only weakly, as evidenced by a low level of binding of FHL-1 relative to that of fH. Using isogenic strains expressing either meningococcal fHbp or gonococcal PorB.1B, we discovered that strains expressing gonococcal PorB.1B in the presence of sialylated lipooligosaccharide bound more fH, more effectively limited C3 deposition, and were more serum resistant than their isogenic counterparts expressing fHbp. Differences in fH binding to these two related pathogens may be important for modulating their individual responses to host immune attack.

Dihydrolipoamide Dehydrogenase of Pseudomonas aeruginosa Is a Surface-Exposed Immune Evasion Protein That Binds Three Members of the Factor H Family and Plasminogen

“…Microbial proteins that bind Factor H and FHL-1 via these domains include Rck from Salmonella enterica and Gpm1 and Pra1 from C. albicans (23,35,44,45). A second group of microbial surface proteins binds the two human regulators either via SCRs 6-7 (e.g., M proteins and Fba from Streptococcus pyogenes, NspA from Neisseria meningitidis, CRASP-1 from B. burgdorferi) or via SCRs 18-20 (e.g., Scl1 from S. pyogenes and Por1B from Neisseria gonorrheae) of Factor H (30,(46)(47)(48). In addition, pathogenic microbes also bind the human terminal complement pathway regulator CFHR1.…”

Characterization of Diverse Subvariants of the Meningococcal Factor H (fH) Binding Protein for Their Ability To Bind fH, To Mediate Serum Resistance, and To Induce Bactericidal Antibodies

“…These results are supported by the findings on a different panel of subvariants that were published by Dunphy et al (7) while our manuscript was under review. It has been elucidated that fHbp binds to short consensus repeat 6 (SCR6) of fH (50). Moreover, the nuclear magnetic resonance structure of the C-terminal portion of fHbp 1.1 (5) and the crystal structure of fHbp 1.1 in complex with fH SCR67 (48) have led to identification of residues important for binding of anti-fHbp antibodies and fH, respectively.…”

Role of Factor H Binding Protein in Neisseria meningitidis Virulence and Its Potential as a Vaccine Candidate To Broadly Protect against Meningococcal Disease

“…fHBP binds preferentially to human fH, while chimpanzee, baboon, or rhesus macaque fHs show less binding or barely bind at all (84). The cocrystal structure of fHBP with human fH SCR6-7 peptide shows the host specificity between the divergent human and nonhuman primate fH SCR6 sequences that would interact with fHBP (61,84). The specificity of fHBP for human fH also helps to explain the observation that bactericidal titers measured with rabbit complement are typically higher than those measured in the presence of human complement (85,86).…”

“…Flow cytometric analysis has demonstrated that SCR domain 6 (SCR6) of fH is the main domain that interacts with fHBP on the surface of N. meningitidis (61). A cocrystal structure shows specific interactions involving both structural domains of fHBP (B24, variant 1.1) with the fH peptide that contains SCR domains 6 and 7 (fH 67 , one of the three SCR regions on fH involved in binding polyanions such as heparin), as shown in Fig.…”

“…Many pathogens, however, have evolved to evade this alternative complement pathway killing by binding fH on the bacterial surface (59). A well-characterized example is PorB.1A from Neisseria gonorrhoeae, which binds to fH short consensus repeat (SCR) domains 18 to 20 (58,(60)(61)(62). Although fH binding proteins have been identified in many pathogens, the sequence and structure of fHBP are unique to N. meningitidis and a few other neisserial species.…”