Identification of the Amidotransferase AsnB1 as Being Responsible formeso-Diaminopimelic Acid Amidation in Lactobacillus plantarum Peptidoglycan
The peptidoglycan (PG) ofLactobacillus plantarumcontains amidatedmeso-diaminopimelic acid (mDAP). The functional role of this PG modification has never been characterized in any bacterial species, except for its impact on PG recognition by receptors of the innate immune system.In silicoanalysis of loci carrying PG biosynthesis genes in theL. plantarumgenome revealed the colocalization of themurEgene, which encodes the ligase catalyzing the addition of mDAP to UDP-N-muramoyl-d-glutamate PG precursors, withasnB1, which encodes a putative asparagine synthase with an N-terminal amidotransferase domain. By gene disruption and complementation experiments, we showed thatasnB1is the amidotransferase involved in mDAP amidation. PG structural analysis revealed that mDAP amidation plays a key role in the control of thel,d-carboxypeptidase DacB activity. In addition, a mutant strain with a defect in mDAP amidation is strongly affected in growth and cell morphology, with filamentation and cell chaining, while a DacB-negative strain displays a phenotype very similar to that of a wild-type strain. These results suggest that mDAP amidation may play a critical role in the control of the septation process.