Immune evasion of Borrelia burgdorferi: mapping of a complement‐inhibitor factor H‐binding site of BbCRASP‐3, a novel member of the Erp protein family

Abstract

The causative agents of Lyme disease, Borrelia burgdorferi s.s., B. garinii, and B. afzelii, differ in their susceptibility to complement‐mediated lysis. This phenomenon apparently depends on the expression of proteins termed complement regulator‐acquiring surface proteins (CRASP) and their binding to the inhibitory plasma proteins factor H and FHL‐1. To characterize these bacterial proteins in more detail we have now isolated from a B. burgdorferi expression library a novel factor H‐binding protein. In accordance with our previous studies this protein was termed BbCRASP‐3 and represents a novel member of the polymorphic Erp (OspE/F‐related) protein family. On the basis of protease accessibility assays using intact spirochetes, BbCRASP‐3 isidentified as a surface‐exposed protein and binds the C‐terminal short consensus repeats of factor H. Applying deletion mutants of BbCRASP‐3, the factor H‐binding site was mapped to the nine‐amino‐acid motif LEVLKKNLK localized at the C‐terminal end of BbCRASP‐3. Factor H bound to BbCRASP‐3 maintains its cofactor activity in factor I‐mediated C3b inactivation. Binding of BbCRASP‐3 to factor H can be inhibited by heparin, a physiological ligand of the complement regulator factor H. Blocking of factor‐H‐binding by soluble BbCRASP‐3 leads to an increase of complement deposition on intermediate serum‐resistant strain ZS7. In conclusion, BbCRASP‐3 has been identified as a novel factor H‐binding protein on B. burgdorferi which by conferring complement resistance to the pathogen may contribute to its persistence in the mammalian host.

Borrelia burgdorferi complement regulator-acquiring surface proteins (BbCRASPs): Expression patterns during the mammal–tick infection cycle

“…Orthologous genes have been identified in all other Lyme disease spirochete genospecies, although it is not yet clear whether or not the encoded proteins bind factor H and FHL-1 (Rogers and Marconi, 2007, and our unpublished results). BbCRASP-3, -4, and -5 lipoproteins all belong to the Erp paralog family, and their respective genes are named erpP, erpC, and erpA, or, collectively, ospE (Stevenson et al, 1996Casjens et al, 2000;Hellwage et al, 2001;Alitalo et al, 2002Alitalo et al, ,2004Kraiczy et al, 2003Kraiczy et al, ,2004aMetts et al, 2003). erp loci are all located on borrelial prophages which replicate as circular episomes known as cp32s .…”

“…produces several different outer surface proteins collectively termed CRASPs (complement regulator-acquiring surface proteins). These lipoproteins share affinities for the host fluid phase negative regulators of complement factor H and/or FHL-1 (factor H-like protein 1) (Hellwage et al, 2001;Kraiczy et al, 2001Kraiczy et al, , 2003Kraiczy et al, , 2004aKraiczy et al, , 2004bAlitalo et al, 2002Alitalo et al, , 2005Stevenson et al, 2002;McDowell et al, 2003;Hartmann et al, 2006;Kraiczy and Würzner, 2006;Herzberger et al, 2007). Those two host proteins promote breakdown of C3b and inactivation of the alternative pathway C3 convertase (Janeway et al, 1999;Kraiczy and Würzner, 2006).…”

Complement Resistance of Borrelia burgdorferi Correlates with the Expression of BbCRASP-1, a Novel Linear Plasmid-encoded Surface Protein That Interacts with Human Factor H and FHL-1 and Is Unrelated to Erp Proteins

“…Our previous studies indicated that moderate or fully complement-resistant B. burgdorferi and Borrelia afzelii strains, but not complementsensitive Borrelia garinii strains, express up to five factor H-and FHL-1-binding surface molecules termed complement regulator-acquiring surface proteins (CRASPs) (13,34,35). According to their ability to differentially bind factor H and FHL-1, CRASPs of complement-resistant B. burgdorferi (BbCRASPs) and B. afzelii (BaCRASPs) strains are divided into three groups: factor H-and FHL-1-binding proteins (BbCRASP-1, BaCRASP-1, BbCRASP-2, and BaCRASP-2), FHL-1-binding proteins (BaCRASP-3), and factor H-binding proteins (BbCRASP-3-5, BaCRASP-4, and BaCRASP-5) (34,36).…”

“…According to their ability to differentially bind factor H and FHL-1, CRASPs of complement-resistant B. burgdorferi (BbCRASPs) and B. afzelii (BaCRASPs) strains are divided into three groups: factor H-and FHL-1-binding proteins (BbCRASP-1, BaCRASP-1, BbCRASP-2, and BaCRASP-2), FHL-1-binding proteins (BaCRASP-3), and factor H-binding proteins (BbCRASP-3-5, BaCRASP-4, and BaCRASP-5) (34,36). More recently, BbCRASP-3 has been characterized on a molecular level and identified as a novel member of the polymorphic Erp (OspE/F-related proteins) family (35). BbCRASP-3 and multiple homologous Erp proteins expressed by virulent B. burgdorferi strains were shown to bind factor H (12,(37)(38)(39)(40).…”

IgM cleavage by Streptococcus suis reduces IgM bound to the bacterial surface and is a novel complement evasion mechanism

“…Streptococcus pyogenes for example has been shown to use the C5a and C3 peptidase ScpA [21], M protein mediated C4BP binding [22] and the C5b-C9 inhibitory protein SIC [23] to circumvent complement. Gram negative Borrelia burgdorferi inhibits complement via multiple FH binding proteins [24] and enterohemorrhagic Escherichia coli can cleave C1-INH and thus enhance its complement inhibitory function [25]. For S. suis complement evasion has not been intensively studied and so far only the sialic acid containing capsule of certain serotypes and factor H binding molecules have been described as complement evasion factors [26,27].…”