Molecular analyses of the interaction of Borrelia hermsii FhbA with the complement regulatory proteins factor H and factor H-like protein 1.
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 that B. 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.
Hovis
Kelley M
KM
Department of Microbiology and Immunology, Medical College of Virginia at Virginia Commonwealth University, Richmond, VA 23298-0678, USA.
Jones
Janice P
JP
Sadlon
Tania
T
Raval
Gauri
G
Gordon
David L
DL
Marconi
Richard T
RT
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D001898:Borrelia / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003180:Complement C3b Inactivator Proteins; D017242:Complement Factor H / Q000378:metabolism*; D016384:Consensus Sequence; D004252:DNA Mutational Analysis; D006801:Humans; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000235:genetics
D001426:Bacterial Proteins; C517621:CFHR1 protein, human; D002352:Carrier Proteins; D003180:Complement C3b Inactivator Proteins; C510009:FH-binding protein A, Borrelia hermsii; D017242:Complement Factor H