The negative regulator of β-lactamase induction AmpD is a N-acetyl-anhydromuramyl-L-alanine amidase

Abstract

Construction of a malE-ampD gene fusion allowed purification of biologically active fusion protein by affinity chromatography. The cloned malE-ampD gene fusion complemented a chromosomal ampD mutation. Purified MalE-AmpD fusion protein was found to have murein amidase activity with a pronounced specificity for 1,6-anhydromuropeptides, the characteristic murein turnover products in Escherichia coli. Being a N-acetyl-anhydromuranmyl-L-alanine amidase AmpD is likely to be involved in recycling of the turnover products. It is suggested that the negative regulatory effect of AmpD is due to the hydrolysis of anhydro-muropeptides which may function as signals for beta-lactamase induction.

Cell-wall recycling and synthesis in Escherichia coli and Pseudomonas aeruginosa – their role in the development of resistance

“…The first indication that this gene may play a critical role in cell-wall recycling stemmed from observations of its influence on blactamase induction [165]. Its specific role as an amidase in recycling was confirmed when it was noticed that the loss of ampD resulted in the accumulation of GlcNAc-anhMurNAc with peptide chains [163,164]. Subsequently, a major increase of anhydromuramyl tripeptides in ampD-deficient E. coli cells led to the identification of an LD-carboxypeptidase LdcA [166].…”

“…AmpD and LdcA E. coli AmpD cleaves the peptide chain exclusively attached to the 1,6-anhydromuramyl moieties [163,164]. The first indication that this gene may play a critical role in cell-wall recycling stemmed from observations of its influence on blactamase induction [165].…”

“…In the case of the peptide components of PG, AmpD amidase cleaves the peptide side chain from UDP-MurNAc resulting in the formation of free tri-, tetra-and pentapeptides (L-Ala-ɣ-D-Glu-meso-DAP-D-Ala-D-Ala) [164]. LdcA carboxypeptidase cleaves the terminal D-alanine from a tetrapeptide resulting in tripeptides [166].…”

Peptidoglycan structure of Salmonella typhimurium growing within cultured mammalian cells

“…Their physiological functions are still uncertain, although they have been implicated in autolysis and/or peptidoglycan recycling (Parquet et al, 1983;Kitano et al, 1986;Goodell and Higgins, 1987;Shockman and Hö ltje, 1994). The relevance of AmiA and AmiB in peptidoglycan recycling has been questioned by the recent finding in E. coli of a muropeptide-permease, AmpG, and a cytosolic N-acetyl-muramyl-L-alanine amidase, AmpD, which apparently mediate the main recycling pathway (Park, 1993;Hö ltje et al, 1994;Jacobs et al, 1994;. Incidentally, a DNA fragment with extensive homology to E. coli ampD has also been identified in S. typhimurium (Hughes et al, 1993).…”

The β-Lactamase Gene Regulator AmpR Is a Tetramer That Recognizes and Binds the d-Ala-d-Ala Motif of Its Repressor UDP-N-acetylmuramic Acid (MurNAc)-pentapeptide

“…In the cytosol, the nonreducing GlcNAc residue is removed from the fragments by the glycosidase NagZ (11)(12)(13) to yield a series of 1,6-anhydroMurNAc-tripeptides, -tetrapeptides, and -pentapeptides. The amidase AmpD cleaves the amide bond linking the remaining sugar, 1,6-anhydroMurNAc, to the peptide stems (14,15), and the resulting pool of monosaccharide and peptide catabolites are subsequently used to build UDP-MurNAc-pentapeptide, an essential anabolite of cell wall synthesis (5). In the absence of ␤-lactams, UDP-MurNAc-pentapeptide binds to AmpR and causes the repression of ampC transcription (16).…”