title: Mutational analyses of the BbCRASP-1 protein of Borrelia burgdorferi identify residues relevant for the architecture and binding of host complement regulators FHL-1 and factor H.
abstract: Borrelia burgdorferi exploits multiple strategies to evade host immune responses. One central immune escape mechanism is the inactivation of the host complement attack by acquisition host complement regulators FHL-1 and factor H via complement regulator-acquiring surface proteins (BbCRASPs). The BbCRASP-1 protein is the first bacterial factor H/FHL-1-binding protein for which the atomic structure has been solved. Previously, 3 regions including the C terminus were identified as putative contact sites for the two complement regulators by the pepspot analysis. Based on the crystallographic structure an in vitro mutagenesis approach was conducted to identify amino acid residues which are relevant for FHL-1 and factor H binding by exchanging single or multiple residues in region 1 and the C-terminally located region 3. Single changes at 4 positions in region 1 either reduced (Lys136, Lys141, Glu147) or completely eliminated (Leu146) binding of both complement regulators. Substitutions clustered within the C-terminal region decreased (Glu234, Lys238, Tyr239, Lys241, Asp244, Thr245) or abolished binding (Lys240, Asp242, Leu246) of both complement regulators. Mapping the mutations onto the atomic structure of BbCRASP-1 reveals that, in contrast to earlier assumption, the C-terminal mutations act indirectly on FHL-1 and factor H binding, whilst the region 1 mutations map the site of direct complement regulator interaction. The elucidation of BbCRASP-1 structure - function may allow development of novel therapeutic strategies against Lyme disease.
authors.affiliation: Institute of Medical Microbiology and Infection Control, University Hospital of Frankfurt, Frankfurt am Main, Paul-Ehrlich-Street 40, D-60596 Frankfurt am Main, Germany. Kraiczy@em.uni-frankfurt.de
authors.forename: Peter
authors.initials: P
authors.lastname: Kraiczy
authors.forename: Christa
authors.initials: C
authors.lastname: Hanssen-Hübner
authors.forename: Veronique
authors.initials: V
authors.lastname: Kitiratschky
authors.forename: Christiane
authors.initials: C
authors.lastname: Brenner
authors.forename: Silke
authors.initials: S
authors.lastname: Besier
authors.forename: Volker
authors.initials: V
authors.lastname: Brade
authors.forename: Markus M
authors.initials: MM
authors.lastname: Simon
authors.forename: Christine
authors.initials: C
authors.lastname: Skerka
authors.forename: Pietro
authors.initials: P
authors.lastname: Roversi
authors.forename: Susan M
authors.initials: SM
authors.lastname: Lea
authors.forename: Brian
authors.initials: B
authors.lastname: Stevenson
authors.forename: Reinhard
authors.initials: R
authors.lastname: Wallich
authors.forename: Peter F
authors.initials: PF
authors.lastname: Zipfel
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D025065:Borrelia burgdorferi / Q000737:chemistry* / Q000235:genetics; D003180:Complement C3b Inactivator Proteins; D017242:Complement Factor H / Q000378:metabolism*; D004252:DNA Mutational Analysis; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins; C517621:CFHR1 protein, human; D003180:Complement C3b Inactivator Proteins; D008565:Membrane Proteins; C440651:complement regulator-acquiring surface proteins, Borrelia burgdorferi; D017242:Complement Factor H