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Title
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Interactions of phage P22 tails with their cellular receptor, Salmonella O-antigen polysaccharide.
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Authors
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U.Baxa,
S.Steinbacher,
S.Miller,
A.Weintraub,
R.Huber,
R.Seckler.
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Ref.
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Biophys J, 1996,
71,
2040-2048.
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PubMed id
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Abstract
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Bacteriophage P22 binds to its cell surface receptor, the repetitive O-antigen
structure in Salmonella lipopolysaccharide, by its six homotrimeric tailspikes.
Receptor binding by soluble tailspikes and the receptor-inactivating
endorhamnosidase activity of the tailspike protein were studied using octa- and
dodecasaccharides comprising two and three O-antigen repeats of Salmonella
enteritidis and Salmonella typhimurium lipopolysaccharides. Wild-type tailspike
protein and three mutants (D392N, D395N, and E359Q) with defective
endorhamnosidase activity were used. Oligosaccharide binding to all three
subunits, measured by a tryptophan fluorescence quench or by fluorescence
depolarization of a coumarin label attached to the reducing end of the
dodecasaccharide, occurs independently. At 10 degrees C, the binding affinities
of all four proteins to oligosaccharides from both bacterial strains are
identical within experimental error, and the binding constants for octa- and
dodecasaccharides are 1 x 10(6) M(-1) and 2 x 10(6) M(-1), proving that two
O-antigen repeats are sufficient for lipopolysaccharide recognition by the
tailspike. Equilibration with the oligosaccharides occurs rapidly, but the
endorhamnosidase produces only one cleavage every 100 s at 10 degrees C or about
2 min(-1) at the bacterial growth temperature. Thus, movement of virions in the
lipopolysaccharide layer before DNA injection may involve the release and
rebinding of individual tailspikes rather than hydrolysis of the O-antigen.
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