Haemophilus Influenzae Protein E Recognizes the C-terminal Domain of Vitronectin and Modulates the Membrane Attack Complex

Mol Microbiol. 2011 Jul;81(1):80-98. doi: 10.1111/j.1365-2958.2011.07678.x. Epub 2011 May 12.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adhesins, Bacterial / genetics
  • Adhesins, Bacterial / metabolism*
  • Amino Acid Substitution
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Blood Bactericidal Activity
  • Cell Line
  • Complement Membrane Attack Complex / metabolism*
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Haemophilus influenzae / immunology*
  • Haemophilus influenzae / pathogenicity
  • Humans
  • Immune Evasion
  • Mutagenesis, Site-Directed
  • Mutant Proteins / genetics
  • Mutant Proteins / metabolism
  • Protein Binding
  • Protein Interaction Mapping*
  • Sequence Deletion
  • Vitronectin / genetics
  • Vitronectin / metabolism*

Substances

  • Adhesins, Bacterial
  • Bacterial Proteins
  • Complement Membrane Attack Complex
  • Mutant Proteins
  • Vitronectin