CspA is a 27-kDa surface-localized lipoprotein encoded by ORF bba68 on lp54 (Fraser et al., 1997; Casjens et al., 2000;
Kraiczy et al., 2004; Brooks et al., 2005). CspA is downregulated or completely turned off in the mammalian host environment as shown by cultivation in dialysis membrane chambers and by incubation of B. burgdorferi in SCH772984 research buy the presence of human blood (Brooks et al., 2003; Tokarz et al., 2004). These observations also are consistent with the results of several studies showing that CspA is not expressed during mammalian infection (or is expressed at a dramatically low level; Brooks et al., 2003; Tokarz et al., 2004; McDowell et al., 2006; Bykowski et al., 2007). Therefore, CspA may be most relevant in serum resistance in the tick vector during the initial bloodmeal. The interaction between FH/FHL-1 and CspA has been mapped to SCR5-7 of FH/FHL-1 (Kraiczy et al., 2004). The
C-terminal 11 amino acids of CspA are required for binding to FH/FHL-1 (Kraiczy et al., 2004). Atezolizumab However, when the CspA crystal structure was solved, it was determined that CspA forms a homodimer and that the C-terminus is important in the interaction of the two CspA molecules (Cordes et al., 2005). Therefore, it is possible that the C-terminus plays an indirect role in FH/FHL-1 binding by stabilizing the homodimer. In fact, when the coiled coil domains of CspA are disrupted, CspA no longer binds FH/FHL-1, leading to the conclusion that binding of FH/FHL-1 to CspA requires tertiary or quaternary level folding (McDowell et al., 2005). When CspA was inactivated in B. burgdorferi, CspA was shown to be essential for serum resistance in vitro, for binding FH to the borrelial surface, and for evading deposition of complement proteins on the bacterial surface (Brooks et al.,
2005; Kenedy et al., 2009). While in vitro data suggest that CspA is relevant in survival of B. burgdorferi in the presence of serum, the role of CspA in the animal model of Lyme disease has not yet been elucidated. CspZ (previously referred to as CRASP-2) is a 27-kDa lipoprotein that has also been identified as a FH-binding protein (Hartmann et al., 2006). CspZ is encoded by ORF bbh06 on plasmid lp28-3. CspZ interacts with the SCR6-7 domain of FH/FHL-1 (Fraser et al., Arachidonate 15-lipoxygenase 1997; Casjens et al., 2000; Hartmann et al., 2006). Whether CspZ is located on the surface of B. burgdorferi is unclear. While CspZ has been detected on the borrelial surface by indirect immunofluorescence, digestion of surface proteins with proteinase K does not degrade CspZ (Hartmann et al., 2006; Coleman et al., 2008). When expressed in the serum-sensitive B. burgdorferi B313 strain, CspZ enhances resistance to serum (Hartmann et al., 2006). Animal studies indicate that CspZ is expressed during mammalian infection; however, CspZ is not essential for infection of mice via tick infestation (Coleman et al., 2008). To date, CspZ is the only B. burgdorferi FH-binding protein that has been investigated in vivo.