Decorin-binding adhesins from Borrelia burgdorferi

Lyme disease is a tick-transmitted infection caused by the spirochete Borre lia burgdorferi. Ticks deposit B. burgdorferi into the dermis of the host, where they eventually become associated with collagen fibres. We demonstrat ed previously that B. burgdorferi is unable to bind collagen, but can bind the collagen-associated proteoglycan decorin and expresses decorin-binding proteins (Dbps). We have now cloned and sequenced two genes encoding the pr oteins, DbpA and DbpB, which have a similar structure, as revealed by circu lar dichroism (CD) spectroscopy of recombinant proteins. Competition experi ments revealed a difference in binding specificity between DbpA and DbpB. W estern blot analysis of proteinase K-treated intact B. burgdorferi and tran smission electron microscopy studies using antibodies raised against recomb inant Dbps demonstrated that these proteins are surface exposed. DbpA effec tively inhibits the attachment of B. burgdorferi to a decorin substrate, wh ereas DbpB had a marginal effect, suggesting a difference in substrate spec ificity between the two Dbps. Polystyrene beads coated with DbpA adhered to a decorin-containing extracellular matrix produced by cultured skin fibrob lasts, whereas beads coated with OspC did not. Taken together, these data s uggest that Dbps are adhesins of the MSCRAMM (microbial surface component-r ecognizing adhesive matrix molecule) family, which mediate B. burgdorferi a ttachment to the extracellular matrix of the host.