Carlos Karan Gurnani Serrano and Matthias Winkle just published their manuscript on ActS.
The integrity of the cell envelope of E. coli relies on the concerted activity of multi‐protein machineries that synthesize the peptidoglycan (PG) and the outer membrane (OM).
Their previous work showed that the depletion of lipopolysaccharide (LPS) export to the OM induces an essential PG remodeling process involving LD‐transpeptidases (LDTs), the glycosyltransferase function of PBP1B and the carboxypeptidase PBP6a. Consequently, cells with defective OM biogenesis lyse if they lack any of these PG enzymes.
Now this research reports that the morphological defects and lysis associated with a ldtF mutant with impaired LPS transport, are alleviated by the loss of the predicted OM‐anchored lipoprotein ActS (formerly YgeR).
It was shown that ActS is an inactive member of LytM‐type peptidoglycan endopeptidases due to a degenerate catalytic domain. ActS is capable of activating all three main periplasmic peptidoglycan amidases, AmiA, AmiB and AmiC, which were previously reported to be activated only by EnvC and/or NlpD. They also suggest that in vivo ActS preferentially activates AmiC and that its function is linked to cell envelope stress.