title: Haemophilus influenzae protein E recognizes the C-terminal domain of vitronectin and modulates the membrane attack complex.
abstract: 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.
authors.affiliation: Medical Microbiology and Medical Protein Chemistry, Department of Laboratory Medicine Malmö, Lund University, Skåne University Hospital, SE-205 02 Malmö, Sweden.
authors.forename: Birendra
authors.initials: B
authors.lastname: Singh
authors.forename: Farshid
authors.initials: F
authors.lastname: Jalalvand
authors.forename: Matthias
authors.initials: M
authors.lastname: Mörgelin
authors.forename: Peter
authors.initials: P
authors.lastname: Zipfel
authors.forename: Anna M
authors.initials: AM
authors.lastname: Blom
authors.forename: Kristian
authors.initials: K
authors.lastname: Riesbeck
mesh_terms: D018829:Adhesins, Bacterial / Q000235:genetics / Q000378:metabolism*; D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001770:Blood Bactericidal Activity; D002460:Cell Line; D015938:Complement Membrane Attack Complex / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D006193:Haemophilus influenzae / Q000276:immunology* / Q000472:pathogenicity; D006801:Humans; D057131:Immune Evasion; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017384:Sequence Deletion; D019096:Vitronectin / Q000235:genetics / Q000378:metabolism*
chemical_list: D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; D015938:Complement Membrane Attack Complex; D050505:Mutant Proteins; D019096:Vitronectin