title: Phage P22 tailspike protein: crystal structure of the head-binding domain at 2.3 A, fully refined structure of the endorhamnosidase at 1.56 A resolution, and the molecular basis of O-antigen recognition and cleavage.
abstract: The tailspike protein of Salmonella phage P22 is a viral adhesion protein with both receptor binding and destroying activities. It recognises the O-antigenic repeating units of cell surface lipopolysaccharide of serogroup A, B and D1 as receptor, but also inactivates its receptor by endoglycosidase (endorhamnosidase) activity. In the final step of bacteriophage P22 assembly six homotrimeric tailspike molecules are non-covalently attached to the DNA injection apparatus, mediated by their N-terminal, head-binding domains. We report the crystal structure of the head-binding domain of P22 tailspike protein at 2.3 A resolution, solved with a recombinant telluromethionine derivative and non-crystallographic symmetry averaging. The trimeric dome-like structure is formed by two perpendicular beta-sheets of five and three strands, respectively in each subunit and caps a three-helix bundle observed in the structure of the C-terminal receptor binding and cleaving fragment, reported here after full refinement at 1.56 A resolution. In the central part of the receptor binding fragment, three parallel beta-helices of 13 complete turns are associated side-by-side, while the three polypeptide strands merge into a single domain towards their C termini, with close interdigitation at the junction to the beta-helix part. Complex structures with receptor fragments from S. typhimurium, S. enteritidis and S. typhi253Ty determined at 1.8 A resolution are described in detail. Insertions into the beta-helix form the O-antigen binding groove, which also harbours the active site residues Asp392, Asp395 and Glu359. In the intact structure of the tailspike protein, head-binding and receptor-binding parts are probably linked by a flexible hinge whose function may be either to deal with shearing forces on the exposed, 150 A long tailspikes or to allow them to bend during the infection process.
authors.affiliation: Max-Planck-Institut für Biochemie, Abteilung für Strukturforschung, Martinsried, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Steinbacher
authors.forename: S
authors.initials: S
authors.lastname: Miller
authors.forename: U
authors.initials: U
authors.lastname: Baxa
authors.forename: N
authors.initials: N
authors.lastname: Budisa
authors.forename: A
authors.initials: A
authors.lastname: Weintraub
authors.forename: R
authors.initials: R
authors.lastname: Seckler
authors.forename: R
authors.initials: R
authors.lastname: Huber
mesh_terms: D000595:Amino Acid Sequence; D017100:Bacteriophage P22 / Q000737:chemistry* / Q000201:enzymology; D001665:Binding Sites; D002240:Carbohydrate Sequence; D018360:Crystallography, X-Ray; D006026:Glycoside Hydrolases / Q000737:chemistry* / Q000378:metabolism; D008715:Methionine / Q000031:analogs & derivatives / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019081:O Antigens / Q000378:metabolism*; D011487:Protein Conformation; D011991:Receptors, Virus / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D012475:Salmonella / Q000737:chemistry / Q000821:virology; D013691:Tellurium / Q000737:chemistry; D017376:Viral Tail Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D019081:O Antigens; D011991:Receptors, Virus; D011994:Recombinant Proteins; D017376:Viral Tail Proteins; C094617:telluromethionine; D008715:Methionine; D006026:Glycoside Hydrolases; C041312:endorhamnosidase; C083268:tailspike protein, bacteriophage; D013691:Tellurium