title: The tailspike protein of Shigella phage Sf6. A structural homolog of Salmonella phage P22 tailspike protein without sequence similarity in the beta-helix domain.
abstract: Bacteriophage Sf6 tailspike protein is functionally equivalent to the well characterized tailspike of Salmonella phage P22, mediating attachment of the viral particle to host cell-surface polysaccharide. However, there is significant sequence similarity between the two 70-kDa polypeptides only in the N-terminal putative capsid-binding domains. The major, central part of P22 tailspike protein, which forms a parallel beta-helix and is responsible for saccharide binding and hydrolysis, lacks detectable sequence homology to the Sf6 protein. After recombinant expression in Escherichia coli as a soluble protein, the Sf6 protein was purified to homogeneity. As shown by circular dichroism and Fourier transform infrared spectroscopy, the secondary structure contents of Sf6 and P22 tailspike proteins are very similar. Both tailspikes are thermostable homotrimers and resist denaturation by SDS at room temperature. The specific endorhamnosidase activities of Sf6 tailspike protein toward fluorescence-labeled dodeca-, deca-, and octasaccharide fragments of Shigella O-antigen suggest a similar active site topology of both proteins. Upon deletion of the N-terminal putative capsid-binding domain, the protein still forms a thermostable, SDS-resistant trimer that has been crystallized. The observations strongly suggest that the tailspike of phage Sf6 is a trimeric parallel beta-helix protein with high structural similarity to its functional homolog from phage P22.
authors.affiliation: Physikalische Biochemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Golm, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Freiberg
authors.forename: Renato
authors.initials: R
authors.lastname: Morona
authors.forename: Luisa
authors.initials: L
authors.lastname: Van den Bosch
authors.forename: Christiane
authors.initials: C
authors.lastname: Jung
authors.forename: Joachim
authors.initials: J
authors.lastname: Behlke
authors.forename: Nils
authors.initials: N
authors.lastname: Carlin
authors.forename: Robert
authors.initials: R
authors.lastname: Seckler
authors.forename: Ulrich
authors.initials: U
authors.lastname: Baxa
mesh_terms: D000595:Amino Acid Sequence; D017100:Bacteriophage P22 / Q000737:chemistry / Q000378:metabolism*; D001483:Base Sequence; D002942:Circular Dichroism; D003001:Cloning, Molecular; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D006026:Glycoside Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D012760:Shigella / Q000821:virology*; D017550:Spectroscopy, Fourier Transform Infrared; D017376:Viral Tail Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D017376:Viral Tail Proteins; D006026:Glycoside Hydrolases; C083268:tailspike protein, bacteriophage