Abstract
The proteinaceous inhibitor of vertebrate lysozymes (Ivy) is produced by a collection of Gram-negative bacteria as a stress response to damage to their essential cell wall component peptidoglycan. A paralog of Ivy, Ivyp2 is produced exclusively by a number of pseudomonads, including Pseudomonas aeruginosa, but this protein does not inhibit the lysozymes, and its function was unknown. In this study, we demonstrate that the production of Ivy (homologs of both Ivyp1 and Ivyp2) correlates with bacteria that do not O-acetylate their peptidoglycan, a modification that controls the activity of the lytic transglycosylases. Furthermore, we show that both Ivy proteins are potent inhibitors of the lytic transglycoslyases, enzymes involved in the biosynthesis and maintenance of peptidoglycan. These data suggest that the true physiological function of the Ivy proteins is to control the autolytic activity of lytic transglycosylases within the periplasm of Gram-negative bacteria that do not produce O-acetylated peptidoglycan and that the inhibition of exogenous lysozyme by Ivy is simply a fortuitous coincidence.
Highlights
The cell envelope represents the only major structural element in bacterial cells, and it extends from the cytoplasmic leaflet of the plasma membrane to the outer layer(s) of wall and capsular polymers
Despite their overall sequence similarity to Ivyc and Ivyp1, these inhibitor of vertebrate lysozymes (Ivy) paralogs do not inhibit lysozyme, and their function remained unknown. We demonstrate that both Ivyp1 and the paralog Ivyp2 inhibit membrane-bound lytic transglycosylase B (MltB) from P. aeruginosa and that the true physiological function of these periplasmic inhibitors may be to control autolysis in cells that do not O-acetylate their PG
The biochemical and structural analysis of the protein encoded by ykfE from E. coli was found to be a potent inhibitor of C-type lysozymes and renamed Ivyc for inhibitor of vertebrate lysozyme [10]
Summary
The cell envelope represents the only major structural element in bacterial cells, and it extends from the cytoplasmic leaflet of the plasma membrane to the outer layer(s) of wall and capsular polymers. Despite their overall sequence similarity to Ivyc and Ivyp1, these Ivy paralogs do not inhibit lysozyme, and their function remained unknown.
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