title: A novel interaction of outer membrane protein A with C4b binding protein mediates serum resistance of Escherichia coli K1.
abstract: Escherichia coli is an important pathogen that causes meningitis in neonates. The development of bacteremia preceding the traversal across the blood-brain barrier is a prerequisite for this pathogen that obviously must survive the bactericidal activity of serum. Here we report that outer membrane protein A (OmpA) of Escherichia coli contributes to serum resistance by binding to C4b binding protein (C4bp), a complement fluid phase regulator. C4bp contains seven identical alpha-chains and one beta-chain linked together with disulfide bridges. We found that OmpA binds the alpha-chain of C4bp, which is composed of eight homologous complement control protein (CCP) modules. Binding studies using mutants of recombinant C4bp that lack one CCP at a time suggest that CCP3 is the major site of interaction with OmpA. Furthermore, we demonstrate that the N terminus of OmpA interacts with C4bp. Binding of C4bp to OmpA is not significantly inhibited in the presence of either C4b or heparin and is not salt sensitive, implying that it is hydrophobic in nature, suggesting a novel interaction between OmpA and C4bp. A compelling observation in this study is that synthetic peptides corresponding to CCP3 sequences block the binding of C4bp to OmpA and also significantly enhance serum bactericidal activity.
authors.affiliation: Division of Infectious Diseases, Childrens Hospital, and Keck School of Medicine, University of Southern California, Los Angeles 90027, USA. pnemani@chla.usc.edu
authors.forename: Nemani V
authors.initials: NV
authors.lastname: Prasadarao
authors.forename: Anna M
authors.initials: AM
authors.lastname: Blom
authors.forename: Bruno O
authors.initials: BO
authors.lastname: Villoutreix
authors.forename: Linette C
authors.initials: LC
authors.lastname: Linsangan
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D001770:Blood Bactericidal Activity / Q000276:immunology*; D001798:Blood Proteins / Q000378:metabolism; D003167:Complement Activation; D003169:Complement Inactivator Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D004926:Escherichia coli / Q000276:immunology* / Q000472:pathogenicity; D006023:Glycoproteins; D006031:Glycosylation; D006801:Humans; D066298:In Vitro Techniques; D008958:Models, Molecular; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001798:Blood Proteins; D003169:Complement Inactivator Proteins; D006023:Glycoproteins; D011994:Recombinant Proteins; C078167:OMPA outer membrane proteins