burgdorferi surface lipoproteins have been identified that can bind the soluble host serum proteins factor H and/or factor H-like protein-1 (FH/FHL-1; Hellwage et al., 2001; Kraiczy et al., 2004; Hartmann et al., 2006). Given that FH-/FHL-1 are negative regulators of complement, it is thought that B. burgdorferi

can learn more evade complement mediated lysis by binding FH/FHL-1 on the bacterial cell surface. Binding of FH/FHL-1 on the B. burgdorferi surface promotes evasion of the alternative pathway of complement and thus promotes the survival of the organism in the mammalian host. Collectively, the FH/FHL-1 binding proteins expressed by B. burgdorferi are referred to as complement regulator-acquiring surface proteins (CRASPs), and these proteins include the OspE-related proteins, CspA and CspZ (Hellwage et al., 2001; Kraiczy et al., 2004; Hartmann et al., 2006). The first FH-binding protein identified was the surface lipoprotein OspE (Lam et al., 1994; Hellwage et al., 2001). Hellwage et al. (2001) made the initial observation that FH/FHL-1 could be detected on Ferrostatin-1 the B. burgdorferi cell surface and that the known outer surface lipoprotein OspE could interact with FH, which was demonstrated by surface plasmon resonance (Hellwage et al., 2001). The OspE-related proteins

have also been referred to as Erps and Crasp-3, -4, and -5 (Stevenson et al., 1996; Kraiczy et al., 2001). OspE expression is upregulated by elevated temperature in vitro and during tick feeding and mammalian infection (Stevenson et al., 1995; Hefty et al., 2001, 2002b). Many B. burgdorferi strains encode multiple OspE-related proteins that bind FH (Alitalo et al., 2002). For instance, the B. burgdorferi strain B31 encodes three OspE-related proteins. These proteins are encoded on different 32-kb circular plasmids (cp32s) by ORFs bbl39, bbp38, and bbn38 (Fraser et al., 1997; Casjens et al., 2000). bbl39 and bbp38 are 100% identical in nucleotide sequence and approximately 80% identical to bbn38 (Casjens et al., 2000).

The OspE lipoproteins bind the however C-terminal short consensus repeats (SCR) of FH (Alitalo et al., 2004); however, the OspE domain important in FH binding has not been fully elucidated. In fact, both N-terminal and C-terminal OspE truncations abolish FH binding, suggesting that binding to FH is discontinuous and likely dependent on a higher-ordered conformation of OspE (Alitalo et al., 2002; Metts et al., 2003; McDowell et al., 2004). In addition to FH binding, OspE also binds host plasminogen at a distinct site from the FH-binding region, and it has been suggested that this interaction may promote spirochete dissemination (Brissette et al., 2009). It is still unclear what role the binding activity of OspE may play in B. burgdorferi virulence and/or Lyme disease pathogenesis. CspA (previously referred to as CRASP-1) was first identified as a FH-binding protein when a B. burgdorferi genomic expression library was screened for clones that could bind FH/FHL-1 (Kraiczy et al.