A fucose-binding superlectin from Enterobacter cloacae with high Lewis and ABO blood group antigen specificity
Bacteria frequently employ carbohydrate-binding proteins, so-called lectins, to colonize and persist in a host. Thus, bacterial lectins are attractive targets for the development of new antiinfectives. To find new potential targets for antiinfectives against pathogenic bacteria, we searched for homologs of Pseudomonas aeruginosa lectins and identified homologs of LecA in Enterobacter species. Here, we recombinantly produced and biophysically characterized a homolog that comprises one LecA domain and one additional novel protein domain. This protein was termed Enterobacter cloacae lectin A (EclA) and found to bind L-fucose. Glycan array analysis revealed a high specificity for the LewisA antigen and the type II H-antigen (blood group O) for EclA, while related antigens LewisX, Y, and B as well as blood group A or B were not bound. We developed a competitive binding assay to quantify blood group antigen binding specificity in solution. Finally, the crystal structure of EclA could be solved in complex with methyl -L-selenofucoside. It revealed the unexpected binding of the carbohydrate ligand to the second domain, which comprises a novel fold that dimerizes via strand-swapping resulting in an intertwined beta sheet.