Molecular basis of host-pathogen interactions: case study of Borrelia afzelii

Number of cases of Lyme disease (LD) increase steadily in Europe every year. Two main causative agents of this disease in European area are Borrelia afzelii and Borrelia garinii. It was shown that various Borrelia species exhibit different pathogenicity which has been shown to depend on the variations in the bacterial adhesins and their interactions with host molecules in the extracellular matrix. Two major representatives of those adhesins are Decorin binding proteins A (DbpA) and B (DbpB) which are able to bind (GAGs) glycosaminoglycans. Minor differences in the tertiary structure and dynamics of DbpA/B across Borrelia species in North America and Europe contribute to different binding patterns of individual GAGs. We will combine solution NMR spectroscopy with hydrogen deuterium exchange mass spectrometry (HDX MS) for a detailed study of interactions between DbpA, DbpB from B. afzelii and GAG, octamer of dermatan sulfate. In the NMR part we will utilize specialized experiments tailored for detection of lysine NH3 groups which are the most probable candidates for interactions with sulfate groups of dermatan. With NMR titration, we will define interacting atoms and use this knowledge for the design of mutant variations in DbpA and DbpB in order to mimic amino acid composition of binding sites in Dbps from other European strains. Since Dbp-GAG interactions are often mediated by flexible regions of Dbps HDX MS is well suited to provide additional information needed for detailed epitope mapping. This in-depth study of Dbpa and DbpB will fill the gap in the knowledge about their binding patterns in European Borrelia.