Selective binding of Borrelia burgdorferi OspE paralogs to factor H and serum proteins from diverse animals: possible expansion of the role of OspE in Lyme disease pathogenesis

Abstract

The binding of Borrelia burgdorferi OspE, OspF, and family 163 (Elp) proteins to factor H/factor H-like protein 1 (FHL-1) and other serum proteins from different animals was assessed. OspE paralogs bound factor H and unidentified serum proteins from a subset of animals, while OspF and Elp proteins did not. These data advance our understanding of factor H binding, the host range of the Lyme spirochetes, and the expanding role of OspE in pathogenesis.

FIG. 1.

Analysis of factor H/FHL-1 binding by the B. burgdorferi B31MI OspE, OspF, and Elp proteins. Recombinant S-tagged fusion proteins (the TIGR-assigned ORF designations are indicated above each lane) were generated, purified, separated by SDS-PAGE (15% Criterion precast gels), and immunoblotted. To assess expression and integrity of the recombinant proteins, a blot was screened with HRP-conjugated S protein (A). The proteins were then tested for factor H/FHL-1 binding by use of the ALBI assay (B), as described in the text. Molecular mass standards are indicated.

FIG.2.

“Reverse” ALBI analyses: analysis of the abilities of recombinant OspE, OspF, and Elp proteins to bind to immobilized serum proteins. Serum proteins from different animals (indicated in each panel) were separated by SDS-PAGE with either 7.5% or 12.5% Criterion precast gels under nonreducing conditions. The proteins were immunoblotted and incubated with individual recombinant S-tagged proteins (100 μg ml⁻¹), as indicated in each panel. Note that the blots shown in panels C and D were screened with BBO39 and BBN39, respectively. Identical results were obtained with BBM38, BBR42, BBO40, and BBP39 (data not shown). In all assays, bound recombinant protein was detected using HRP-conjugated (conj.) S protein. All methods were as described in the text. Purified human factor H (FH) was included as a positive control with all immunoblots. The location of factor H on the immunoblots presented in panels A and B is indicated by an arrow for reference. Note that in panel E the serum proteins were separated using reducing conditions and were screened with goat α-human factor H antiserum. With longer exposure, factor H was detected in all animals except duck, horse, rat, and chicken.