Structural Conservation of Neurotropism-associated VspA within the Variable Borrelia Vsp-OspC Lipoprotein Family

Abstract

Vsp surface lipoproteins are serotype-defining antigens of relapsing fever spirochetes that undergo multiphasic antigenic variation to avoid the immune response. One of these proteins, VspA of Borrelia turicatae, is also associated with neurotropism in infected mice. Vsp proteins are highly polymorphic in sequence, which may relate to their specific antibody reactivities and host cell interactions. To determine whether sequence variations affect protein structure, we compared B. turicatae VspA with three related proteins: VspB of B. turicatae, Vsp26 of the relapsing fever agent Borrelia hermsii, and OspC of the Lyme disease spirochete Borrelia burgdorferi. Recombinant non-lipidated proteins were purified by affinity or ion exchange chromatography. Circular dichroism spectra revealed similar, highly ␣-helical secondary structures for all four proteins. In vitro assays demonstrated proteaseresistant, thermostable Vsp cores starting at a conserved serine at position 34 (Ser 34 ). All proteins aggregate as dimers in solution. In situ trypsin treatment and surface protein cross-linking showed that the native lipoproteins also form protease-resistant dimers. These findings indicate that Vsp proteins have a common compact fold and that their established functions are based on localized polymorphisms. Two forms of VspA crystals suitable for structure determination by x-ray diffraction methods have been obtained.

Bacterial Lipoproteins Can Disseminate from the Periphery to Inflame the Brain

“…For this we injected intraperitoneally new groups of uninfected or Bt1-infected RAG1 Ϫ/Ϫ mice simultaneously with 100 g/kg of Eu-albumin and 100 g/kg of Sm-LVsp1 to determine whether the presence of Eu-LVsp1 increased the dissemination to the brain of Eu-albumin, which has a molecular weight three times larger than that of LVsp1. 21 The results showed that the dissemination of Eu-albumin to brain did not change in the presence of Eu-LVsp1 (Supplemental Figure 4, see http://ajp.amjpathol.org; P ϭ NS). We concluded that the increase in dissemination of LVsp1 to the brain as a result of infection was unlikely to be explained by nonspecific opening of the BBB.…”

“…The following proteins were used in this study: (1) LVsp1 and LVsp2, the major outer membrane lipoproteins of serotypes 1 (Bt1) and 2 (Bt2), respectively, of the relapsing fever spirochete B. turicatae; they were prepared by detergent extraction from cultures of Bt1 or Bt2 spirochetes as before 20 ; (2) rVsp1 was kindly provided by Wolfram Zuckert, PhD (University of Kansas Medical Center) 21 ; and (3) mouse albumin was purchased from Sigma (St. Louis, MO, category number A1056). Protein purity was confirmed by SDS-polyacrylamide gel electrophoresis (Supplemental Figure 1, see http://ajp.amjpathol.org) and by Western blot with monoclonal antibodies anti Vsp1 (1H12) or anti Vsp2 (5F12) 20,22 (not shown).…”

Crystal Structure of Lyme Disease Variable Surface Antigen VlsE of Borrelia burgdorferi

“…Analytical ultracentrifugation and gel filtration chromatography experiments were performed in our laboratories in analogy to analyses of other surface proteins (19) and indicate that recombinant VlsE1 is primarily monomeric in solution (data not shown). In the crystal structure, the interface between neighboring VlsE1 molecules in the asymmetric unit buries ϳ13% of the accessible surface area of each monomer (Fig.…”

Antigen polymorphism in Borrelia hermsii , a clonal pathogenic bacterium

“…The positions of the sequence motifs are approximately to scale and their order is according to occurrence in respective alleles. Also shown are the relative positions of predicted ␣-helices in the mature proteins (27). Two of the repeats, A and C, occur first in the sequence encoding the signal peptide.…”