Balanced biosynthesis of major membrane components through regulated degradation of the committed enzyme of lipid A biosynthesis by the AAA protease FtsH (HflB) in Escherichia coli

Abstract

SummaryThe suppressor mutation, named sfhC21, that allows Escherichia coli ftsH null mutant cells to survive was found to be an allele of fabZ encoding R-3-hydroxyacyl-ACP dehydrase, involved in a key step of fatty acid biosynthesis, and appears to upregulate the dehydrase. The ftsH1(Ts) mutation increased the amount of lipopolysaccharide at 42ЊC. This was accompanied by a dramatic increase in the amount of UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase [the lpxC (envA) gene product] involved in the committed step of lipid A biosynthesis. Pulse-chase experiments and in vitro assays with purified components showed that FtsH, the AAA-type membrane-bound metalloprotease, degrades the deacetylase. Genetic evidence also indicated that the FtsH protease activity for the deacetylase might be affected when acyl-ACP pools were altered. The biosynthesis of phospholipids and the lipid A moiety of lipopolysaccharide, both of which derive their fatty acyl chains from the same R-3-hydroxyacyl-ACP pool, is regulated by FtsH.

Crosstalk between the lipopolysaccharide and phospholipid pathways during outer membrane biogenesis in Escherichia coli

“…In the first scenario, due to the fact that LPS and phospholipids biosynthetic pathways both derive their precursor molecules from β-hydroxymyristoyl-ACP, it was accepted that competition for this common substrate influences the regulation of LpxC (11). In other words, LpxC degradation would help conserve substrates for phospholipids synthesis.…”

“…Briefly, the first reaction step catalyzed by LpxA is highly unfavorable, which makes the proceeding enzyme, LpxC, the first committed enzyme (10). LpxC is regulated by the protease FtsH (11,12), and we recently postulated that the negative feedback signal arises from lipid A disaccharide, the substrate for LpxK (9). Furthermore, FtsH regulates WaaA (formerly called KdtA), an enzyme downstream of LpxC (13).…”

“…Because both pathways are synchronized to ensure a proper balance of membrane components (11,14), studies underpinning the underlying mechanisms would appear valuable. There are a number of experimental findings that indicate the existence of strong links between both biosynthetic pathways (11,15,16). Thus, in the context of outer membrane biogenesis, the role involving phospholipids cannot be ignored in the study of LPS regulation.…”

Reconstitution of Membrane Proteolysis by FtsH

“…Our results indicate that the dislocation-accompanied proteolytic event can occur without involving other cellular factors such as the Sec translocation channel. (23) and ftsH3::kan (17) into CU141. AD1680 was used for purification of YccA-HA-His 6 -Myc and YccA11-HA-His 6 -Myc as the Prc (Tsp) protease was found to cleave the C-terminal periplasmic tails of these proteins in vivo (data not shown).…”

Region 2.1 of the Escherichia coli heat-shock sigma factor RpoH (σ 32) is necessary but not sufficient for degradation by the FtsH protease

“…Apart from general protein quality-control functions in degrading misfolded innermembrane proteins, the FtsH protease has important regulatory functions (reviewed by Ito & Akiyama, 2005). Its active site is oriented towards the cytoplasm and it degrades specifically a number of soluble proteins such as LpxC, the key enzyme in LPS biosynthesis (Führer et al, 2006;Ogura et al, 1999), phage l proteins cII, cIII and Xis (Herman et al, 1997;Kihara et al, 1997;Leffers & Gottesman, 1998;Shotland et al, 1997), and the sigma factor RpoH. It is still largely unknown how this repertoire of entirely unrelated substrates is recognized and processed by the FtsH protease.…”