Ivy Proteins as Guardians of Bacterial Cell Wall Integrity: Regulation of Lytic Transglycosylases Explored

Lytic transglycosylases (LTs) are bacterial enzymes involved in biosynthesis and maintenance of the peptidoglycan cell wall. LTs are reported to be regulated by two paralogs of Inhibitor of Vertebrate Lysozymes: Ivyp1 and Ivyp2. This study investigated the regulatory dynamics between the soluble LT (SltB1), and Ivy paralogs as putative regulators in Pseudomonas aeruginosa (PA). The secondary objective was to delineate the critical roles played by a glutamic acid at position 135 in SltB1 and a histidine at position 62 in Ivyp1 in governing their molecular interaction through site directed mutagenesis. Isolated SltB1 shows no lytic activity in our assay, in spite of the fact that it was correctly folded and pure, suggesting a potential dependency on a cofactor or coenzyme for activation. In addition, Biolayer Interferometry revealed that isolated SltB1 is not subject to regulation by either Ivyp1 or Ivyp2. These results challenge Ivy's characterization as a general inhibitor for all LTs suggesting that SltB1 is regulated by other factors.