Enzymic and Molecular Properties of Base-Plate Parts of Bacteriophage P22

Abstract

Using 14C-labeled Salmonella bacterial cells as the substrate, the enzymic and molecular properties of the base-plate parts of phage P22 were studied. The base-plate part consisted of a single protein species which cleaved extensively the O-antigen of S. typhimurium, S. schottmuelleri and with somewhat slower rate that of S. typhi, releasing oligosaccharide products with rhamnose at the reducing end. Much less cleavage was observed with a strain of S. typhimurium lysogenic for P22 and no significant reaction with S. anatum, S. newington and S. minneapolis. The base-plate part enzyme was a very heat-stable protein and only 10-20% loss was observed after treatment at 85.degree. C for 5 min. The pH optimum of the enzyme was around 7.5 and the glycosidase activity was not influenced by the ionic strength (25-250 mM) of the medium or the presence of Mg2+. The MW of the base-plate part was 320,000 by sedimentation equilibrium. Dodecylsulfate-acrylamide gel electrophoresis revealed a single band of MW 77,000, indicating that a single base-plate part corresponds to a tetramer of identical subunits. Circular dichroism spectra of P22 base-plate parts showed a major contribution of .beta. structure. The protein was rich in acidic amino acids, glycine and serine.