Evidence for N----O acetyl migration as the mechanism for O acetylation of peptidoglycan in Proteus mirabilis

Abstract

0-acetylated peptidoglycan was purified from Proteus mirabilis grown in the presence of specifically radiolabelled glucosamine derivatives, and the migration of the radiolabel was monitored. Mild-base hydrolysis of the isolated peptidoglycan (to release ester-linked acetate) from cells grown in the presence of 40 , Following the lysis of invading microorganisms, mammalian tissues clear cellular debris, including peptidoglycan (PG), very rapidly through the action of the hydrolytic enzymes of either phagocytic cells or serum. However, in some instances, large-molecular-weight fragments of PG have been observed to persist and circulate in the host organism. These large PG fragments have been shown to induce diverse pathobiological and pathophysiological effects, many of which have been recently reviewed (36). Some of these include the induction of slow-wave sleep, complement activation, pyrogenicity, modulation of blastogenesis, and arthritogenicity. In vivo studies with the pathogens Staphylococcus aureus and Neisseria gonorrhoeae indicated that the phenomenon of PG persistence is directly attributable to the presence of numerous O-acetyl substituents on the glycan backbone (5,15,24,34,40). 0-acetylated PG has been observed in a number of bacteria, including many pathogenic species, both gram positive (e.g., S. aureus [17,41]) and gram negative (e.g., N. gonorrhoeae [40] and Proteus mirabilis [14]). 0 acetylation of PG occurs at the C-6 hydroxyl group of N-acetylmuramyl residues, producing the corresponding 2,6-diacetylmuramyl derivative. This modification to PG inhibits the hydrolytic activity of lysozymes (reference 13 and references therein), presumably through steric hindrance since the C-6 hydroxyl moieties of the substrate directly participate in its binding to the active-site cleft of the enzyme (3, 23). The PG of some species of eubacteria has been reported to be 0 acetylated up to 70%, thereby conferring both intrinsic and complete resistance to lysozyme hydrolysis (30). (1, 7), and the biological significance of this modification was discerned soon after (6). Whereas its role in resistance to muramidases and the consequences of such have been well documented, very little is known concerning the biosynthetic process involved with the 0 acetylation of PG. There is evidence to suggest that 0 acetylation occurs after nascent PG strands have been both attached and cross-linked to the preexisting sacculus (10,18,(26)(27)(28)39). By pulse-chasing radiolabelled N-acetyl-D-glucosamine (GlcNAc) into the PG of P. mirabilis, Gmeiner and Kroll (18) revealed that only non-O-acetylated PG subunits are incorporated into the growing polymer. It has also been observed that the 0 acetylation of PG continues in a cell-free biosynthetic system of P. mirabilis PG (30). , using a similar experimental strategy, obtained analogous results with N. gonorrhoeae. Indeed, searches for lipid (bactoprenyl)-linked N-acetylglucosaminyl-N,O-diacetylmuramyl pentapeptide precursors in either the cytoplasm or the cytoplasmic membrane pro...

aarC, an essential gene involved in density-dependent regulation of the 2'-N-acetyltransferase in Providencia stuartii

“…Alternatively, aarC may regulate gene expression in response to other density-dependent signals such as oxygen and/or nutrient depletion or growth rate. The physiological significance of this regulation may be related the role of aac(2Ј)-Ia in the O acetylation of peptidoglycan, a modification which affects degradation by muramidases and thus may control autolytic activity (4)(5)(6)19). The decrease in aac(2Ј)-Ia at high density may occur in preparation for changes in cell morphology that occur during the transition to stationary phase.…”

The pgdA Gene Encodes for a PeptidoglycanN-Acetylglucosamine Deacetylase in Streptococcus pneumoniae

“…Putative Peptidoglycan Deacetylases in Other BacteriaNon-acetylated hexosamine residues have been reported to be present in the peptidoglycans of many bacteria, especially in Bacillus species, although no genes encoding for such an enzyme were identified (25)(26)(27)(28)(29). In searching the data bases for hypothetical proteins similar in sequence to the pneumococcal PgdA protein we found other putative peptidoglycan deacetylases in bacterial species having partially deacetylated peptidoglycan: three hypothetical proteins in Bacillus subtilis (GenBank TM accession numbers AAC46306, BAA23389, and CAA74511) and one NodB homolog protein in both Bacillus stearothermophilus (GenBank TM accession number B47692) and Bacillus cereus (GenBank TM accession number CAB40600).…”

Characterization and transcriptional regulation of the 2'-N-acetyltransferase gene from Providencia stuartii

“…The RimJ protein has also been implicated in the thermoregulation of Pap pilin expression (32). In Proteus spp., the presence of 0-acetylated peptidoglycan occurs from the action of an N-0-acetyltransferase, which transfers an acetyl group from the N-2 position to a hydroxyl group at the C-6 position of N-acetylmuramic acid (11). In addition, acetyltransferases are important in antibiotic resistance, in which resistance to both chloramphenicol and the aminoglycosides can be mediated by these proteins.…”