Peptidoglycan+Amino+Acid+Recycling

=__Peptidoglycan Amino Acid Recycling__=

Peptidoglycan (murein) undergoes extensive degradation and resynthesis, during periods of normal bacterial growth. Indeed, it is estimated that 40% to 50% of peptidoglycan is broken down and reused each generation (Plumbridge, 2009).

During the last few decades, the pathways for recycling both the peptide and amino sugar components of peptidoglycan have been analysed, and genes involved in the process identified. In fact, most of the genes involved encode enzymes whose sole function is to recover and reuse the material produced during peptidoglycan turnover implying that this pathway serves an important function in the cell (Plumbridge, 2009). It has been hypothesised that when faced with a sudden loss of carbon, peptidoglycan recycling may provide enough nutrients to allow the cell to complete a round of cell divisions and enter stationary phase. Alternatively it is thought that the high levels of competition for food in the large intestine between bacteria may cause the ability to recycle peptidoglycan to infer a distinct survival advantage (Park and Uehara, 2008). However, it should be noted that peptidoglycan recycling is not crucial to cell survival under laboratory conditions, and with one exception mutations in the genes known to be involved in recycling yield no obvious phenotype (Park and Uehara, 2008).

Some of these enzymes responsible for peptidoglycan recycling also serve a subsidiary function in processes such as beta-lactamase induction (Plumbridge, 2009), and it is for this reason the peptidoglycan recycling pathways are of particular interest to us.

__**Peptide Recycling**__ Radiolabelling studies by Goodell in 1985 demonstrated that the tripeptide, tetrapeptide and dipeptide shed by E. coli from the murein sacculus could be reused by cells to synthesise murein. They showed that while the tripeptide may recycled directly by E. coli, the tetrapeptide lost its carboxy-terminal D-Ala before being used and the dipeptide was degraded to individual amino acids before uptake.

__**Specific Proteins involved in Amino Acid Recycling:**__
 * AmiD
 * AmpG
 * AmpD
 * LdcA
 * MpaA
 * MppA
 * Mpl
 * OppBCDF
 * PepD
 * YcjG