An Alternative and Conserved Cell Wall Enzyme That Can Substitute for the Lipid II Synthase MurG.

The cell wall is a stress-bearing structure and a unifying trait in bacteria. Without exception, synthesis of the cell wall involves formation of the precursor molecule lipid II by the activity of the essential biosynthetic enzyme MurG, which is encoded in the division and cell wall synthesis () gene cluster. Here, we present the discovery of a cell wall enzyme that can substitute for MurG. A mutant of lacking a significant part of the cluster, including , surprisingly produced lipid II and wild-type peptidoglycan. Genomic analysis identified a distant homologue, which encodes a putative enzyme that shares only around 31% amino acid sequence identity with MurG. We show that this enzyme can replace the canonical MurG, and we therefore designated it MglA. Orthologues of are present in 38% of all genomes of and members of the sister genus CRISPR interference experiments showed that can also functionally replace in , thus validating its bioactivity and demonstrating that it is active in multiple genera. All together, these results identify MglA as a bona fide lipid II synthase, thus demonstrating plasticity in cell wall synthesis. Almost all bacteria are surrounded by a cell wall, which protects cells from environmental harm. Formation of the cell wall requires the precursor molecule lipid II, which in bacteria is universally synthesized by the conserved and essential lipid II synthase MurG. We here exploit the unique ability of an actinobacterial strain capable of growing with or without its cell wall to discover an alternative lipid II synthase, MglA. Although this enzyme bears only weak sequence similarity to MurG, it can functionally replace MurG and can even do so in organisms that naturally have only a canonical MurG. The observation that MglA proteins are found in many actinobacteria highlights the plasticity in cell wall synthesis in these bacteria and demonstrates that important new cell wall biosynthetic enzymes remain to be discovered.