Multi-drug resistant (MDR) pathogens have become a high-profile threat to public health. Rapidly spreading worldwide, they are responsible for increased mortality in hospital-acquired infections. The “anti-adhesion” therapy is a new tactic to fight against bacterial infections. It aims to block the infectious process at its initial stage by preventing bacteria from adhering to host tissues via lectin-glycoconjugate interactions.
Burkholderia cenocepacia is a MDR, Gram-negative, opportunistic bacterium usually responsible for “Cepacia Syndrome”; a condition affecting cystic fibrosis patients in which rapid decline of respiratory function can lead to respiratory failure and even death. B. cenocepacia features a carbohydrate-binding protein with dual specificity: BC2L-C. The two distinct carbohydrate recognition domains (CRDs) presented by this superlectin play a role in cell-adhesion: while the LecB-like C-terminal domain specifically binds to bacterial mannosides, the N-terminal domain binds to human fucosides.[1,2] BC2L-C’s N-terminal domain is particularly interesting because of its affinity for human histo-blood group epitopes. Additionally, it presents a novel fucose binding site and a fold previously unseen in lectins.
In order to perform rational design of antagonists for BC2L-C-Nter, extensive structural study of its binding site is necessary. In turn, this required the production and purification of a new recombinant form of BC2L-C-Nter. Isothermal titration calorimetry (ITC) confirmed micromolar affinity for fucosylated oligosaccharides as well as millimolar affinity for monosaccharides, corroborating previous studies and thus, validating the new construct.
Additionally, it allowed co-crystallization with oligosaccharides for the first time. Crystal structures of the complexes with H-type 1 and H-type 3 blood-group antigens were solved by X-ray crystallography at 1.6 and 1.9 Å resolutions, respectively (see Figure 1). Analysis of the contributions of the additional glycan moieties offered insights at the atomic level on how the gain of affinity can be rationalized, leading the way towards high-affinity ligand design. Furthermore, the vicinity of the CRD was mapped and two potential binding pockets were identified. Thanks to this information, fragment screening provided a small library of ligand candidates for the two CRD-adjacent sites.
With experimental validation of the fragments under way, synthetic approaches are being tested to connect the monosaccharide core to fragments. Our latest results will be described in the communication.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 765581.
- Sulak, O.; Cioci, G.; Delia, M.; Lahmann, M.; Varrot, A.; Imberty, A.; Wimmerova, M. A TNF-like trimeric lectin domain from Burkholderia cenocepacia with specificity for fucosylated human histo-blood group antigens. Structure 2010, 18, 59–72.
- Sulak, O.; Cioci, G.; Lameignere, E.; Balloy, V.; Round, A.; Gutsche, I.; Malinovska, L. et al. Burkholderia cenocepacia BC2L-C is a super lectin with dual specificity and proinflammatory activity. PLoS Pathog. 2011, 7 (9), e1002238.
- Work performed by K. Lal as part of the collaboration between the present project and his PhD thesis: “Design of antagonists for bacterial lectin BC2L-C by molecular modeling”.