Structure of decorin binding protein B from Borrelia burgdorferi and its interactions with glycosaminoglycans.

Decorin-binding proteins (DBPs), DBPA and DBPB, are surface lipoproteins on Borrelia burgdorferi, the causative agent of Lyme disease. DBPs bind to the connective tissue proteoglycan decorin and facilitate tissue colonization by the bacterium. Although structural and biochemical properties of DBPA are well understood, little is known about DBPB. In current work, we determined the solution structure of DBPB from strain B31 of B. burgdorferi and characterized its interactions with glycosaminoglycans (GAGs). Our structure shows that DBPB adopts the same topology as DBPA, but possesses a much shorter terminal helix, resulting in a longer unstructured C-terminal tail, which is also rich in basic amino acids. Characterization of DBPB-GAG interactions reveals that, despite similar GAG affinities of DBPA and DBPB, the primary GAG-binding sites in DBPB are different from DBPA. In particular, our results indicate that lysines in the C-terminus of DBPB are vital to DBPB's ability to bind GAGs whereas C-terminal tail for DBPA from strain B31 only plays a minor role in facilitating GAG bindings. Furthermore, the traditional GAG-binding pocket important to DBPA-GAG interactions is only secondary to DBPB's GAG-binding ability.