Autolytic Enzyme System of Streptococcus faecalis V. Nature of the Autolysin-Cell Wall Complex and Its Relationship to Properties of the Autolytic Enzyme of Streptococcus faecalis

Abstract

Cell walls from exponential-phase cultures of Streptococcus faecalis ATCC 9790 contain an autolysin (a β- N -acetylmuramide glycanhydrolase, E.C. 3.2.1.17) which has been isolated from trypsin-speeded wall autolysates. The autolysin, which was excluded from Bio-Gel P-60, was further fractionated by diethylaminoethyl (DEAE)-cellulose chromatography or filtration on Bio-Gel P-200. After DEAE-cellulose chromatography, which removed most of the wall polysaccharide, autolysin activity was extremely labile and was rapidly lost at −20 C, even in the presence of albumin. The P-60-excluded enzyme was rapidly bound by walls at both 37 C (50% bound in about 1 min) and 0 C (50% bound in less than 4 min). Wall-bound autolysin could not be removed by 1.0 m ammonium acetate ( p H 6.9). Autolysin was also bound by walls that had been extracted with 10% trichloroacetic acid or treated with 0.01 n periodate, suggesting that the nonpeptidoglycan wall polymers are not important for binding. Wall-bound autolysin was more stable than the soluble enzyme to proteinase digestion, acetone (40%), 8 m urea (at 0 C), or to inactivation at 56 C. Two bacterial neutral proteinases (which do not hydrolyze ester bonds) activated latent wall-bound autolysin, suggesting that activation results from the cleavage of one or more peptide bonds. The group A streptococcal proteinase activated latent autolysin but differed from the other proteinases in that it did not inactivate soluble autolysin. The results suggest that the autolysin is not covalently linked to the wall. The high affinity of the walls for the autolysin appears to be responsible for the firm, not easily reversed binding.