A Novel Interaction Between Type IV Pili ofNeisseria gonorrhoeaeand the Human Complement Regulator C4b-Binding Protein

Abstract

C4b-binding protein (C4BP) is an important plasma inhibitor of the classical pathway of complement activation. Several bacterial pathogens bind C4BP, which may contribute to their virulence. In the present report we demonstrate that isolated type IV pili from Neisseria gonorrhoeae bind human C4BP in a dose-dependent and saturable manner. C4BP consists of seven identical α-chains and one β-chain linked together with disulfide bridges. We found that pili bind to the α-chain of C4BP, which is composed of eight homologous complement control protein (CCP) domains. From the results of an inhibition assay with C4b and a competition assay in which we tested mutants of C4BP lacking individual CCPs, we concluded that the binding area for pili is localized to CCP1 and CCP2 of the α-chain. The binding between pili and C4BP was abolished at 0.25 M NaCl, implying that it is based mostly on ionic interactions, similarly to what have been observed for C4b-C4BP binding. Furthermore, the N-terminal part of PilC, a structural component of pili, appeared to be responsible for binding of C4BP. Membrane cofactor protein, previously shown to be a receptor for pathogenic N. gonorrhoeae on the surface of epithelial cells, competed with C4BP for binding to pili only at high concentrations, suggesting that different parts of pili are involved in these two interactions. Accordingly, high concentrations of C4BP were required to inhibit binding of N. gonorrhoeae to Chang conjunctiva cells, and no inhibition of binding was observed with cervical epithelial cells.

A Novel Interaction of Outer Membrane Protein A with C4b Binding Protein Mediates Serum Resistance of Escherichia coli K1

“…It could be that other molecules, such as S-fimbriae, also bind C4bp to a lesser extent. Such an interaction of C4bp with type IV pili has been demonstrated in N. gonorrhoeae in addition to Por1B/1A, highlighting the role of more than one molecule binding to C4bp (7).…”

“…Interestingly, mAb 104, which is directed against CCP1 of the ␣-chain of C4bp, did not cause significant inhibition of the rC4bp-OmpA interaction. Yet, this Ab has been previously shown to fully block binding between CCP1 of the ␣-chain of C4bp and C4b (22), N. gonorrhoeae (7), and streptococcal M proteins (28), suggesting a novel site of interaction between OmpA and C4bp. The moderate survival rates of OmpA Ϫ E. coli, E91, could be due to the presence of capsular polysaccharide K1, which is composed of sialic acid residues.…”

“…Furthermore, Por1A as well as Por1B bind to C4bp, and blocking of this interaction renders the bacteria serum sensitive (6). Finally, type IV pili of Neisseria also bind C4bp; thus, gonococci have several mechanisms that act cooperatively to mediate serum resistance (7). C4bp is present in human plasma at concentrations of 200 -250 g/ml and is present in plasma in several forms, the major one composed of seven identical 70-kDa subunits (␣-chains) and one 45-kDa subunit (␤-chain) (8).…”

Interaction with C4b-Binding Protein Contributes to Nontypeable Haemophilus influenzae Serum Resistance

“…Complement resistance is crucial for bacterial virulence and binding of complement inhibitors such as vitronectin, C4BP and factor H (FH) is an efficient strategy used by several serum resistant pathogens (12,35). M. catarrhalis, S. pyogenes, and E. coli K1 are bacteria which express surface molecules binding C4BP protecting the bacteria against the classical/ lectin pathways (22)(23)(24).…”

Interaction with Type IV Pili Induces Structural Changes in the Bacterial Outer Membrane Secretin PilQ

“…A number of these minor pilins are thought to be integrated into the growing pilus (20). An adhesin protein (PilC) has been shown to bind to the host epithelial receptors CD 46 (21) and C4B (22). PilC also plays a role in the assembly process and a minor pilin, PilV, has been implicated in its functional presentation (20).…”