Release of soluble peptidoglycan from growing conococci: demonstration of anhydro-muramyl-containing fragments

Previous analysis of soluble peptidoglycan (PG) fragments released by exponentially growing gonococci implicated the combined action of both hexosaminidase and amidase activities in PG turnover. Current studies further characterized PG fragments which were labeled in the glycan with D-glucosamine and in the peptide moiety with meso-diaminopimelic acid of L- and D-alanine. Labeled PG fragments were isolated by gel filtration and characterized on the bases of (i) KD values, (ii) free amino group analysis using fluorodinitrobenzene, (iii) borohydride reduction, (iv) alkali-catalyzed beta-elimination, (v) paper chromatography in various solvents, (vi) electrophoretic mobility at various pH values, (vii) digestibility by Charonia lampas glycosidases, and (viii) content of labeled D- and L-alanine. A set of well-characterized PG fragments was used as standards. The monomer fraction (the major extracellular product) was found to contain two components. Most (about 80%) appeared to be N-acetylglucosaminyl-beta-1 leads to 4-1,6-anhydro-N-acetylmuramyl-L-ala-D-glu-meso-diaminopimelic acid; the remainder was the corresponding disaccharide tetrapeptide containing a C-terminal D-alanine. An unusual feature of these products was the presence of the anhydro-muramyl (non-reducing) ends, reflecting the activity of a gonococcal transglycosylase, and the near absence of products containing detectable reducing ends. Otherwise, the structures of the monomer fragments were typical of those expected for a gram-negative bacterium (chemotype I). The corresponding peptide-cross-linked dimer and the free disaccharide also contained nonreducing ends, exclusively. Free peptides (products of amidase activity) consisted of both tripeptide and tetrapeptide. In summary, all gonococci examined appear to possess an unusual transglycosylase activity which contributes to the release of soluble PG fragments containing nonreducing, anhydro-muramyl ends. The release of these fragments in vivo might be a unique aspect of gonococci-host interactions.