Fig 8. Model of DacA1’s role in balancing PG synthesis and degradation.

DacA1 removes the 5^th D-ala residue of the PG side stem and determines which side stem can be used as donor for transpeptidation. By removing the 5^th D-ala residue, DacA1 also allows ShyA to cleave crosslinks between strands by producing its preferred substrate, tetrapeptide-containing side stems. In the absence of DacA1, there is an increased amount of pentapeptides in the PG sacculus, hindering ShyA’s ability to cleave crosslinks. This reduction in endopeptidase activity disrupts the balance between PG synthesis and degradation.