title: Bacteriophage Tailspikes and Bacterial O-Antigens as a Model System to Study Weak-Affinity Protein-Polysaccharide Interactions.
abstract: Understanding interactions of bacterial surface polysaccharides with receptor protein scaffolds is important for the development of antibiotic therapies. The corresponding protein recognition domains frequently form low-affinity complexes with polysaccharides that are difficult to address with experimental techniques due to the conformational flexibility of the polysaccharide. In this work, we studied the tailspike protein (TSP) of the bacteriophage Sf6. Sf6TSP binds and hydrolyzes the high-rhamnose, serotype Y O-antigen polysaccharide of the Gram-negative bacterium Shigella flexneri (S. flexneri) as a first step of bacteriophage infection. Spectroscopic analyses and enzymatic cleavage assays confirmed that Sf6TSP binds long stretches of this polysaccharide. Crystal structure analysis and saturation transfer difference (STD) NMR spectroscopy using an enhanced method to interpret the data permitted the detailed description of affinity contributions and flexibility in an Sf6TSP-octasaccharide complex. Dodecasaccharide fragments corresponding to three repeating units of the O-antigen in complex with Sf6TSP were studied computationally by molecular dynamics simulations. They showed that distortion away from the low-energy solution conformation found in the octasaccharide complex is necessary for ligand binding. This is in agreement with a weak-affinity functional polysaccharide-protein contact that facilitates correct placement and thus hydrolysis of the polysaccharide close to the catalytic residues. Our simulations stress that the flexibility of glycan epitopes together with a small number of specific protein contacts provide the driving force for Sf6TSP-polysaccharide complex formation in an overall weak-affinity interaction system.
authors.affiliation: Max Planck Institute of Colloids and Interfaces , Am Mühlenberg 1, 14476 Potsdam, Germany.
authors.forename: Yu
authors.initials: Y
authors.lastname: Kang
authors.affiliation: Max-Delbrück-Centrum für Molekulare Medizin in der Helmholtz-Gemeinschaft , Robert-Rössle-Str. 10, 13125 Berlin, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Gohlke
authors.affiliation: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University , S-106 91 Stockholm, Sweden.
authors.forename: Olof
authors.initials: O
authors.lastname: Engström
authors.affiliation: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University , S-106 91 Stockholm, Sweden.
authors.forename: Christoffer
authors.initials: C
authors.lastname: Hamark
authors.affiliation: Physikalische Biochemie, Universität Potsdam , Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany.
authors.forename: Tom
authors.initials: T
authors.lastname: Scheidt
authors.affiliation: Physikalische Biochemie, Universität Potsdam , Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Kunstmann
authors.affiliation: Max-Delbrück-Centrum für Molekulare Medizin in der Helmholtz-Gemeinschaft , Robert-Rössle-Str. 10, 13125 Berlin, Germany.|Institut für Chemie und Biochemie, Freie Universität , Takustr. 6, 14195 Berlin, Germany.
authors.forename: Udo
authors.initials: U
authors.lastname: Heinemann
authors.affiliation: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University , S-106 91 Stockholm, Sweden.
authors.forename: Göran
authors.initials: G
authors.lastname: Widmalm
authors.affiliation: Max Planck Institute of Colloids and Interfaces , Am Mühlenberg 1, 14476 Potsdam, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Santer
authors.affiliation: Physikalische Biochemie, Universität Potsdam , Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Barbirz
mesh_terms: D001435:Bacteriophages; D001665:Binding Sites; D006026:Glycoside Hydrolases; D056004:Molecular Dynamics Simulation; D019081:O Antigens / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D012763:Shigella flexneri / Q000737:chemistry*; D017376:Viral Tail Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D019081:O Antigens; D017376:Viral Tail Proteins; D006026:Glycoside Hydrolases; C083268:tailspike protein, bacteriophage