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.
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.
Kraiczy
Peter
P
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
Hanssen-Hübner
Christa
C
Kitiratschky
Veronique
V
Brenner
Christiane
C
Besier
Silke
S
Brade
Volker
V
Simon
Markus M
MM
Skerka
Christine
C
Roversi
Pietro
P
Lea
Susan M
SM
Stevenson
Brian
B
Wallich
Reinhard
R
Zipfel
Peter F
PF
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
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