Increasing the Affinity of an O-Antigen Polysaccharide Binding Site in Shigella Flexneri Bacteriophage Sf6 Tailspike Protein

We analysed the tailspike from bacteriophage Sf6 in complex with the O-polysaccharide of the pathogen Shigella flexneri. The conformational space populated by the polyrhamnose backbone of the S. flexneri O-polysaccharide as studied by an octasaccharide in complex with Sf6TSP could be well described with 2D 1H,1H-trNOESY NMR, utilizing a combination of methine-methine and methine-methyl correlations. The results are in good agreement with the conformations obtained from molecular dynamics (MD) simulations. To examine the impact of amino acid exchanges in the glycan binding site of Sf6TSP, MD simulations were used to predict increased O-polysaccharide binding affinities. We used surface plasmon resonance on S. flexneri O-polysaccharide surfaces to measure affinity increases in the obtained mutants.