A peptidoglycan N-deacetylase specific for anhydroMurNAc chain termini in Agrobacterium tumefaciens

Abstract

During growth, bacteria remodel and recycle their peptidoglycan. A key family of peptidoglycan degrading enzymes is the lytic transglycosylases, which produce anhydromuropeptides, a modification that caps the peptidoglycan chains and contributes to bacterial virulence. Previously it was reported that the polar-growing Gram-negative plant pathogen Agrobacterium tumefaciens lacks anhydromuropeptides. Here, we report the identification of an enzyme, MdaA, which specifically removes the acetyl group from anhydromuropeptide chain termini in A. tumefaciens, resolving this apparent anomaly. A. tumefaciens lacking MdaA accumulates canonical anhydromuropeptides, while MdaA was able to deacetylate anhydro-N-acetyl muramic acid in purified sacculi that lack this modification. As for other peptidoglycan deacetylases, MdaA belongs to the CE4 family of carbohydrate esterases but harbors an unusual Cys residue in its active site. MdaA is conserved in other polar-growing bacteria, suggesting a possible link between peptidoglycan chain terminus deacetylation and polar growth.