Subsystem: Recycling of Peptidoglycan Amino Acids
This subsystem's description is:
Bacteria break down and reuse over 60% of the peptidoglycan (PG)of their side wall each generation; recycling of newly made peptidoglycan during septum synthesis occurs at an even faster rate. Gram-negative bacteria living in the colon tend to have a complete repertoire of enzymes for recycling, whereas other organisms have a more limited arsenal.
PG degradation products released into the periplasm by endopeptidases, transglycosidases and amidases are available for uptake by AmpG permease and can enter the recycling pathway (right side of the accompanying Illustration). Recycling is not essential under laboratory conditions.
For more information, please check out the description and the additional notes tabs, below
| Literature References | How bacteria consume their own exoskeletons (turnover and recycling of cell wall peptidoglycan). Park JT Microbiology and molecular biology reviews : MMBR 2008 Jun | 18535144 |
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| Diagram | Functional Roles | Subsystem Spreadsheet | Description | Additional Notes | |||||||||
Bacteria break down and reuse over 60% of the peptidoglycan (PG)of their side wall each generation; recycling of newly made peptidoglycan during septum synthesis occurs at an even faster rate. Gram-negative bacteria living in the colon tend to have a complete repertoire of enzymes for recycling, whereas other organisms have a more limited arsenal. PG degradation products released into the periplasm by endopeptidases, transglycosidases and amidases are available for uptake by AmpG permease and can enter the recycling pathway (right side of the accompanying Illustration). Recycling is not essential under laboratory conditions. AmpG: the key permease is a membrane protein predicted to have 10 transmembrane segments. The ampG gene and yajG, coded upstream of ampG, form an operon. However, it has been shown that yajG, a putative lipoprotein, was not involved in either β-lactamase induction or the expression of AmpG. AmpG, which belongs to the major facilitator superfamily, transports relatively large molecules (MW 992). GlcNAc-anhMurNAc-peptides, the primary products of the action of lytic transglycosylases on PG, are the compounds imported by AmpG. AmpD: cleaves the anhMurNAc-L-Ala bond. AmpD functioning in the cytoplasm rapidly cleaves the anhMurNAc-peptides without destroying the UDP-MurNAc-pentapeptide needed for the synthesis of PG. It contains a zinc ion that was shown to be essential for activity. LdcA: the peptidase that removes D-Ala from L-Ala-{gamma}-D-Glu-meso-Dap-D-Ala (tetrapeptide), disaccharide-tetrapeptide, anh-disaccharide-tetrapeptide, MurNAc-tetrapeptide, and UDP-MurNAc-tetrapeptide. Among the 11 genes involved in recycling, a mutation in the ldcA gene is the only known mutation that produces a phenotype. MpaA: enzyme that cleaves the {gamma}-D-Glu-Dap bond. YcjG: converts L-Ala-D-Glu to L-Ala-L-Glu; belongs to the enolase superfamily. Mpl: UDP-N-Acetylmuramate:L-Alanyl-{gamma}-D-Glutamyl- meso-Diaminopimelate Ligase. AmiD: Outer Membrane Anhydro-N-Acetylmuramyl- L-Ala Amidase. In addition to AmpD, some organisms have a second enzyme with anhMurNAc-L-Ala amidase activity. The amiD gene product has a short signal sequence and a lipobox motif (L14AGC), followed by Ala, which suggested that AmiD is a lipoprotein destined for the outer membrane MppA: Periplasmic Murein Peptide-Binding Protein. All pertinent references are given in the Functional Roles page. | |||||||||||||
