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Haemophilus influenzae protein E recognizes the C‐terminal domain of vitronectin and modulates the membrane attack complex
Author(s) -
Singh Birendra,
Jalalvand Farshid,
Mörgelin Matthias,
Zipfel Peter,
Blom Anna M.,
Riesbeck Kristian
Publication year - 2011
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2011.07678.x
Subject(s) - biology , haemophilus influenzae , vitronectin , bacterial outer membrane , complement system , innate immune system , bacterial adhesin , microbiology and biotechnology , complement membrane attack complex , escherichia coli , immune system , mutant , classical complement pathway , mutagenesis , biochemistry , fibronectin , immunology , cell , gene , antibiotics
Summary Haemophilus influenzae protein E (PE) is a 16 kDa adhesin that induces a pro‐inflammatory immune response in lung epithelial cells. The active epithelial binding region comprising amino acids PE 84–108 also interferes with complement‐mediated bacterial killing by capturing vitronectin (Vn) that prevents complement deposition and formation of the membrane attack complex (MAC). Here, the interaction between PE and Vn was characterized using site‐directed mutagenesis. Protein E variants were produced both in soluble forms and in surface‐expressed molecules on Escherichia coli . Mutations within PE 84–108 in the full‐length molecule revealed that K85 and R86 residues were important for the Vn binding. Bactericidal activity against H. influenzae was higher in human serum pre‐treated with full‐length PE as compared with serum incubated with PE K85E, R86D , suggesting that PE quenched Vn. A series of truncated Vn molecules revealed that the C‐terminal domain comprising Vn 353–363 harboured the major binding region for PE. Interestingly, MAC deposition was significantly higher on mutants devoid of PE due to a decreased Vn‐binding capacity when compared with wild‐type H. influenzae . Our results define a fine‐tuned interaction between H. influenzae and the innate immune system, and identify the mode of control of the MAC that is important for pathogen complement evasion.