Open AccessMolecular Analyses of the Interaction ofBorrelia hermsiiFhbA with the Complement Regulatory Proteins Factor H and Factor H-Like Protein 1
Author(s) -
Kelley M. Hovis,
Janice P. Jones,
Tania Sadlon,
Gauri Raval,
David L. Gordon,
Richard T. Marconi
Publication year - 2006
Publication title -
infection and immunity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.508
H-Index - 220
eISSN - 1070-6313
pISSN - 0019-9567
DOI - 10.1128/iai.74.4.2007-2014.2006
Subject(s) - biology , borrelia , factor h , microbiology and biotechnology , complement (music) , bacterial protein , complement factor i , complement system , computational biology , genetics , bacteria , borrelia burgdorferi , gene , antibody , complementation , phenotype
Borrelia hermsii , the primary etiological agent of tick-borne relapsing fever in North America, binds the complement regulatory protein factor H (FH) as a means of evading opsonophagocytosis and the alternative complement pathway. The ability of FH-binding protein A (FhbA) to bind FH-like protein 1 (FHL-1) has not been assessed previously. In this study, using a whole-cell absorption assay, we demonstrated thatB. hermsii absorbs both FH and FHL-1 from human serum. Consistent with this, affinity ligand binding immunoblot analyses revealed that FH constructs spanning short consensus repeats 1 to 7 and 16 to 20 bind to FhbA. To investigate the molecular basis of the interaction of FhbA with FH/FHL-1, recombinant FhbA truncated proteins were generated and tested for FH/FHL-1 binding. Binding required determinants located in both the N- and C-terminal domains of FhbA, suggesting that long-range intramolecular interactions are involved in the formation and presentation of the FH/FHL-1-binding pocket. To identify specific FhbA residues involved in binding, random mutagenesis was performed. These analyses identified a loop region of FhbA that may serve as a contact point for FH/FHL-1. The data presented here expand our understanding of the pathogenic mechanisms of the relapsing fever spirochetes and of the molecular nature of the interaction between FH/FHL-1 and FhbA.