Abstract
Lipopolysaccharides (LPS) in the outer membrane of Gram-negative bacteria provide the first line of defense against antibiotics and other harmful compounds. LPS biosynthesis critically depends on LpxC catalyzing the first committed enzyme in this process. In Escherichia coli, the cellular concentration of LpxC is adjusted in a growth rate-dependent manner by the FtsH protease making sure that LPS biosynthesis is coordinated with the cellular demand. As a result, LpxC is stable in fast-growing cells and prone to degradation in slow-growing cells. One of the factors involved in this process is the alarmone guanosine tetraphosphate (ppGpp) but previous studies suggested the involvement of yet unknown factors in LpxC degradation. We established a quantitative proteomics approach aiming at the identification of proteins that are associated with LpxC and/or FtsH at high or low growth rates. The identification of known LpxC and FtsH interactors validated our approach. A number of proteins involved in fatty acid biosynthesis and degradation, including the central regulator FadR, were found in the LpxC and/or FtsH interactomes. Another protein associated with LpxC and FtsH was WaaH, a LPS-modifying enzyme. When overproduced, several members of the LpxC/FtsH interactomes were able to modulate LpxC proteolysis. Our results go beyond the previously established link between LPS and phospholipid biosynthesis and uncover a far-reaching network that controls LPS production by involving multiple enzymes in fatty acid metabolism, phospholipid biosynthesis and LPS modification.
Highlights
Gram-negative bacteria like Escherichia coli are protected from external threats by two membranes mainly composed of PL
Proteins associated with Strep-LpxC and maltose binding protein (MBP)-FtsH were identified from cells harvested at different growth rates
The spatial and temporal control of LPS biosynthesis is vitally important for Gram-negative bacteria and several enzymes in this process are essential in E. coli making them attractive antimicrobial targets
Summary
LPS consist of three parts, the membrane-anchor lipid A, the connecting core oligosaccharide and the O-antigen (Raetz and Whitfield, 2002; Bertani and Ruiz, 2018). FabZ catalyzes the first committed step of PL biosynthesis and competes with LpxA for the common precursor R-3hydroxymyristoyl-ACP. To maintain a healthy balance between LPS and PL biosynthesis and to prevent toxic LPS accumulation in the periplasm, the amount of the LpxC enzyme is tightly controlled by the FtsH protease (Ogura et al, 1999). This activity renders the protease essential in Escherichia coli. An ftsH deletion strain only survives in the presence of hyperactive FabZ that counter-balances the high LpxC levels and prevents LPS overproduction (Ogura et al, 1999)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have