From Genome to Proteome to Elucidation of Reactions for All Eleven Known Lytic Transglycosylases from Pseudomonas aeruginosa

An enzyme superfamily, the lytic transglycosylases (LTs), occupies the space between the two membranes of Gram‐negative bacteria. LTs catalyze the non‐hydrolytic cleavage of the bacterial peptidoglycan cell‐wall polymer. This reaction is central to the growth of the cell wall, for excavating the cell wall for protein insertion, and for monitoring the cell wall so as to initiate resistance responses to cell‐wall‐acting antibiotics. The nefarious Gram‐negative pathogen Pseudomonas aeruginosa encodes eleven LTs. With few exceptions, their substrates and functions are unknown. Each P. aeruginosa LT was expressed as a soluble protein and evaluated with a panel of substrates (both simple and complex mimetics of their natural substrates). Thirty‐one distinct products distinguish these LTs with respect to substrate recognition, catalytic activity, and relative exolytic or endolytic ability. These properties are foundational to an understanding of the LTs as catalysts and as antibiotic targets. The lytic transglycosylases (LTs) are glycoside‐cleaving enzymes found in Gram‐negative bacteria. Their diversity of structure contrasts with a common substrate: the peptidoglycan of the bacterial cell wall. By the systematic evaluation of synthetic peptidoglycans and the polymeric peptidoglycan, 11 LTs of Pseudomonas aeruginosa are now characterized with respect to their substrate recognition, catalytic activity, and exolytic or endolytic preference.