Identification and Characterization of a Linear-Plasmid-Encoded Factor H-Binding Protein (FhbA) of the Relapsing Fever Spirochete Borrelia hermsii

Abstract

In North America, tick-borne relapsing fever (TBRF) is caused by the spirochete species Borrelia hermsii, Borrelia parkeri, and Borrelia turicatae. We previously demonstrated that some isolates of B. hermsii and B. parkeri are capable of binding factor H and that cell-bound factor H can participate in the factor I-mediated cleavage of C3b. Isolates that bound factor H expressed a factor H-binding protein (FHBP) that we estimated to be approximately 19 to 20 kDa in size and thus, pending further characterization, temporarily designated FHBP19. Until this report, none of the FHBPs of the TBRF spirochetes had been characterized. Here we have recovered the gene encoding the FHBP of B. hermsii YOR from a lambda ZAP II library and determined its sequence. The gene encodes a full-length protein of 22.7 kDa, which after processing is predicted to be 20.5 kDa. This protein, which we redesignate factor H-binding protein A (FhbA), is unique to B. hermsii. Two-dimensional pulsed-field gel electrophoresis and hybridization analyses revealed that the B. hermsii gene encoding FhbA is a single genetic locus that maps to a linear plasmid of approximately 220 kb. The general properties of FhbA were also assessed. The protein was found to be surface exposed and lipidated. Analysis of the antibody response to FhbA in infected mice revealed that it is antigenic during infection, indicating expression during infection. The identification and characterization of FhbA provides further insight into the molecular mechanisms of pathogenesis of the relapsing fever spirochetes.

Dual Binding Specificity of a Borrelia hermsii-Associated Complement Regulator-Acquiring Surface Protein for Factor H and Plasminogen Discloses a Putative Virulence Factor of Relapsing Fever Spirochetes

“…The previous findings that the relapsing fever spirochete B. hermsii expresses a receptor for FH, FhbA, and that surface-bound FH facilitates factor I-mediated cleavage of C3b suggest a suitable strategy of the pathogen to evade the first-line host defense via the complement system (18). FH binding has been reported for a number of bacterial species such as S. pyogenes (group A streptococcus) (50), Neisseria gonorrhoeae (10, 51), S. pneumoniae (11,13,52), B. burgdorferi (24), Borrelia afzelii (25), Borrelia recurrentis (53), Borrelia duttonii (53), Borrelia parkeri (17), and B. hermsii (18,19).…”

“…FH binding has been reported for a number of bacterial species such as S. pyogenes (group A streptococcus) (50), Neisseria gonorrhoeae (10, 51), S. pneumoniae (11,13,52), B. burgdorferi (24), Borrelia afzelii (25), Borrelia recurrentis (53), Borrelia duttonii (53), Borrelia parkeri (17), and B. hermsii (18,19). Moreover, for B. hermsii YOR it was found that it specifically binds both FH and FHL-1 via FhbA and that FH and FHL-1 interact with FhbA through the SCR domains 1-7 and SCR16 -20 (19).…”

“…In contrast to FH and FHL-1, the precise function(s) of the FHR proteins is currently unknown. For B. hermsii, surfacebound FH was shown to participate as a cofactor for factor I-mediated cleavage of C3b (17)(18)(19). Furthermore, for the closely related spirochete Borrelia burgdorferi, the causal agent of Lyme disease, a strong correlation between the serum resistance of a given isolate and its expression profile of FH-binding outer surface lipoproteins, termed complement regulator-acquiring surface proteins (CRASP), was reported (20 -28).…”

Complement Factor H-Binding Protein, a Putative Virulence Determinant of Borrelia hermsii, Is an Antigenic Target for Protective B1b Lymphocytes

“…PCR and ligation-independent cloning of FhbA were performed as described by Marconi and colleagues (6). Plasmids were transformed into Escherichia coli NovaBlue cells (Novagen), and sequence analysis of the inserts was performed by Thomas Jefferson University's Nucleic Acid Core Facility.…”

“…The random expression of different Vmps during infection results in the outgrowth of new serotypes and allows evasion of the adaptive immune response. Recently, a strategy by which B. hermsii also evades the innate immune system has been proposed (6). This is based on the ability of B. hermsii to bind factor H, a serum complement regulatory protein.…”