The tailspike protein of Shigella phage Sf6. A structural homolog of Salmonella phage P22 tailspike protein without sequence similarity in the beta-helix domain.
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.
Freiberg
Alexander
A
Physikalische Biochemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Golm, Germany.
Morona
Renato
R
Van den Bosch
Luisa
L
Jung
Christiane
C
Behlke
Joachim
J
Carlin
Nils
N
Seckler
Robert
R
Baxa
Ulrich
U
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*
D017931:DNA Primers; D017376:Viral Tail Proteins; D006026:Glycoside Hydrolases; C083268:tailspike protein, bacteriophage