Glycosphingolipid-binding protein of Borrelia burgdorferi sensu lato

The binding of Borrelia burgdorferi, the causative agent of Lyme disease, to glycosphingolipids present in various types of cells was examined. B. burgdorferi bound specifically to galactosylceramide (GalCer) and glucosylceramide (GlcCer) but not to other glycosphingolipids, as determined by a thin-layer chromatography (TLC) overlay assay. The binding specificity of B. burgdorferi to various glycosphingolipids suggested that the binding receptor in this species is ceramide monohexoside. The levels of binding of B. burgdorferi virulent strain 297 to GlcCer, sulfatide, lactosylceramide, and galactosylgloboside were 56.2, 1.6, 15.9, and 9.7%, respectively, relative to that to GalCer. Virulent low-passage strains of B. burgdorferi were serially subcultured in BSK II medium, and the resultant high-passage strains were not capable of infecting mice and did not induce footpad swelling. The levels of binding of the low-passage strains to GalCer on TLC plates and to CHO-K1 cells in vitro were threefold higher than those of high-passage strains. Binding was not affected by pretreatment of Borrelia with monospecific anti-outer surface protein C (OspC) antiserum. These results indicated that the binding of Borrelia to glycosphingolipid expressed on the cell surface plays an essential role in infection of mammalian hosts. However, OspC was not associated with binding. The necessity of the sugar and N-acyl moieties in GalCer for the binding of Borrelia was shown by a TLC overlay assay using chemically modified GalCer. Furthermore, three proteins, 67-kDa protein, 62-kDa Hsp60, and 41-kDa flagellin, were involved in binding of B. burgdorferi to GalCer, as shown by blotting assay using biotinylated GalCer as a probe.