Contribution of the Infection-Associated Complement Regulator-Acquiring Surface Protein 4 (ErpC) to Complement Resistance ofBorrelia burgdorferi

Abstract

<jats:p><jats:italic>Borrelia burgdorferi</jats:italic>evades complement-mediated killing by interacting with complement regulators through distinct complement regulator-acquiring surface proteins (CRASPs). Here, we extend our analyses to the contribution of CRASP-4 in mediating complement resistance of<jats:italic>B. burgdorferi</jats:italic>and its interaction with human complement regulators. CRASP-4 (also known as ErpC) was immobilized onto magnetic beads and used to capture proteins from human serum. Following Western blotting, factor H (CFH), CFH-related protein 1 (CFHR1), CFHR2, and CFHR5 were identified as ligands of CRASP-4. To analyze the impact of native CRASP-4 on mediating survival of serum-sensitive cells in human serum, a<jats:italic>B. garinii</jats:italic>strain was generated that ectopically expresses CRASP-4. CRASP-4-producing bacteria bound CFHR1, CFHR2, and CFHR5 but not CFH. In addition, transformed spirochetes deposited significant amounts of lethal complement components on their surface and were susceptible to human serum, thus indicating that CRASP-4 plays a subordinate role in complement resistance of<jats:italic>B. burgdorferi</jats:italic>.</jats:p>

Versatile Roles of CspA Orthologs in Complement Inactivation of Serum-Resistant Lyme Disease Spirochetes

“…Regrettably, available molecular tools that were successfully engineered for gene inactivation in B. burgdorferi completely failed in B. afzelii and B. spielmanii. However, previous studies conclusively demonstrated that lipoproteins from B. burgdorferi retained their biological function and still interacted with various host proteins when ectopically produced in B. garinii G1 (13,14,47). Thus, we decided to employ this serum-sensitive B. garinii strain as a surrogate to overcome the aforementioned technical limitations and investigate CspA-mediated serum resistance of viable cells.…”

“…To confirm localization of native CspA orthologs on the spirochetal surface, protease accessibility assays using proteinase K (Sigma-Aldrich, Taufkirchen, Germany) were performed as previously described (11,13,47).…”

“…Deposition of activated complement components C3, C6, and C5b-9 (TCC) on the borrelial surface was detected by immunofluorescence microscopy after incubation of spirochetes with 25% active NHS as previously described (13,47).…”

BBA70 of Borrelia burgdorferi Is a Novel Plasminogen-binding Protein

“…For B. burgdorferi, a number of plasminogen-binding proteins have been reported, including OspA (31) and OspC (32), BPBP (30), and more recently B. burgdorferi enolase (34 -36). Of note, the functionally related but genetically heterologous complement regulator-acquiring surface proteins CspA, CspZ, ErpP, ErpC, and ErpA all bind plasminogen in addition to binding various host-derived complement regulators (28,29,(63)(64)(65)(66). Other pathogenic microorganisms have proteins that also bind both plasminogen and complement regulators, such as factor H, factor H-like protein 1, factor H-related protein-1, or C4b-binding protein (23,26,27,(67)(68)(69).…”

A Short-Term Borrelia burgdorferi Infection Model Identifies Tissue Tropisms and Bloodstream Survival Conferred by Adhesion Proteins

“…The differentially regulated B. burgdorferi surface protein CspA (32)(33)(34)(35) and some of the OspE-related protein family members, including ErpA (36,37), ErpP (37), and ErpC (38,39), all act similarly by recruitment of complement regulator factor H (FH) and factor H-like protein-1 (FHL-1) or complement factor H-related proteins (CFHR), presumably to the surface of the bacterium, although the majority of studies have been performed using recombinant protein. FH, FHL-1, and the CFHRs inhibit the alternative complement cascade by cleaving C3b.…”