Biosynthesis of osmoregulated periplasmic glucans in Escherichia coli: the membrane-bound and the soluble periplasmic phosphoglycerol transferases are encoded by the same gene

Abstract

In Escherichia coli, osmoregulated periplasmic glucans (OPGs) are highly substituted by phosphoglycerol, phosphoethanolamine and succinyl residues. A two-step model was proposed to account for phosphoglycerol substitution: first, the membrane-bound phosphoglycerol transferase I transfers residues from membrane phosphatidylglycerol to nascent OPG molecules; second, the periplasmic phosphoglycerol transferase II swaps residues from one OPG molecule to another. Gene opgB was reported to encode phosphoglycerol transferase I. In this study, we demonstrate that the periplasmic enzyme II is a soluble form of the membrane-bound enzyme I. In addition, timing of OPG substitution was investigated. OPG substitution by succinyl residues occurs rapidly, probably during the backbone polymerization, whereas phosphoglycerol addition is a very progressive process. Thus, both phosphoglycerol transferase activities appear biologically necessary for complete OPG substitution.

Proteolytic Cleavage Inactivates the Staphylococcus aureus Lipoteichoic Acid Synthase

“…MdoB catalyzes the transfer of GroP subunits from the membrane lipid PG onto periplasmic oligosaccharides under lowosmolarity conditions. Interestingly, similar to LtaS, MdoB consists of an N-terminal domain with multiple TM helices and a C-terminal extracellular enzymatic domain (31). The enzymatic domain of MdoB is also cleaved during bacterial growth, by an as yet unknown protease also speculated to be a signal peptidase and released from the membrane into the periplasmic space (31).…”

“…Interestingly, similar to LtaS, MdoB consists of an N-terminal domain with multiple TM helices and a C-terminal extracellular enzymatic domain (31). The enzymatic domain of MdoB is also cleaved during bacterial growth, by an as yet unknown protease also speculated to be a signal peptidase and released from the membrane into the periplasmic space (31). Recently, a model was proposed in which the full-length MdoB enzyme transfers GroP from the lipid PG onto nascent oligosaccharide molecules, while the cleaved protein is thought to swap GroP subunits from one oligosaccharide molecule to another (31).…”

Swarm and swim motilities of Salmonella enterica serovar Typhimurium and role of osmoregulated periplasmic glucans

“…100 mMos Mol -1 ) and their synthesis progressively diminishes at higher osmolarity growth conditions [3,5,6,28,33]. In spite of high levels of opgGH RNA transcripts (Figure 4), no OPG are detected in cells grown on regular LB broth media [5,6].…”

“…The central cytoplasmic region of OpgH shares strong structural identity with glucosyl-transferases in which several aspartic acid residues are needed for its catalytic activity [17,28,29]. A ligandbinding site ( 346 Dx 348 D, accession number cd04191) for OpgH has also been identified in the conserved domain structure database [30].…”

“…In order to maximize OPG synthesis, researchers have used nutrient sufficient but hypoosmotic conditions (i.e., LB with-out salts, ~100 mMos Mol -1 ) to grow E. coli, S. flexneri and Salmonella sp. [5,6,28]. Normalizing the opgGH transcript levels to LB-no salts growth conditions, we compared transcript levels from wild-type cells grown in LB containing up to 0.8 M NaCl.…”