Microbes bind complement inhibitor factor H via a common site

• Published in: PLoS pathogens 2013-04, Vol.9 (4), p.e1003308-e1003308
• Main Authors: Meri, T, Amdahl, H, Lehtinen, M J, Hyvärinen, S, McDowell, J V, Bhattacharjee, A, Meri, S, Marconi, R, Goldman, A, Jokiranta, T S
• Format: Article
• Language: English
• Subjects: Bacteria - genetics; Bacteria - immunology; Bacteria - metabolism; Bacteria - pathogenicity; Binding Sites; Binding sites (Biochemistry); Biology; Bordetella pertussis - genetics; Bordetella pertussis - immunology; Bordetella pertussis - metabolism; Bordetella pertussis - pathogenicity; Borrelia - genetics; Borrelia - immunology; Borrelia - metabolism; Borrelia - pathogenicity; Candida albicans - genetics; Candida albicans - immunology; Candida albicans - metabolism; Candida albicans - pathogenicity; Cell Membrane - metabolism; Complement Activation; Complement Factor H - chemistry; Complement Factor H - metabolism; Crystal structure; Haemophilus influenzae - genetics; Haemophilus influenzae - immunology; Haemophilus influenzae - metabolism; Haemophilus influenzae - pathogenicity; Health aspects; Host-parasite relationships; Humans; Pathogenic microorganisms; Physiological aspects; Plasma; Protein Binding; Protein Structure, Tertiary; Proteins; Pseudomonas aeruginosa - genetics; Pseudomonas aeruginosa - immunology; Pseudomonas aeruginosa - metabolism; Pseudomonas aeruginosa - pathogenicity; Staphylococcus aureus - genetics; Staphylococcus aureus - immunology; Staphylococcus aureus - metabolism; Staphylococcus aureus - pathogenicity; Streptococcus infections; Streptococcus pneumoniae - genetics; Streptococcus pneumoniae - immunology; Streptococcus pneumoniae - metabolism; Streptococcus pneumoniae - pathogenicity; Target recognition
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1003308

To cause infections microbes need to evade host defense systems, one of these being the evolutionarily old and important arm of innate immunity, the alternative pathway of complement. It can attack all kinds of targets and is tightly controlled in plasma and on host cells by plasma complement regulator factor H (FH). FH binds simultaneously to host cell surface structures such as heparin or glycosaminoglycans via domain 20 and to the main complement opsonin C3b via domain 19. Many pathogenic microbes protect themselves from complement by recruiting host FH. We analyzed how and why different microbes bind FH via domains 19-20 (FH19-20). We used a selection of FH19-20 point mutants to reveal the binding sites of several microbial proteins and whole microbes (Haemophilus influenzae, Bordetella pertussis, Pseudomonas aeruginosa, Streptococcus pneumonia, Candida albicans, Borrelia burgdorferi, and Borrelia hermsii). We show that all studied microbes use the same binding region located on one side of domain 20. Binding of FH to the microbial proteins was inhibited with heparin showing that the common microbial binding site overlaps with the heparin site needed for efficient binding of FH to host cells. Surprisingly, the microbial proteins enhanced binding of FH19-20 to C3b and down-regulation of complement activation. We show that this is caused by formation of a tripartite complex between the microbial protein, FH, and C3b. In this study we reveal that seven microbes representing different phyla utilize a common binding site on the domain 20 of FH for complement evasion. Binding via this site not only mimics the glycosaminoglycans of the host cells, but also enhances function of FH on the microbial surfaces via the novel mechanism of tripartite complex formation. This is a unique example of convergent evolution resulting in enhanced immune evasion of important pathogens via utilization of a "superevasion site."