Undecaprenyl Phosphate Synthesis

Area of Science:

• Bacterial cell envelope biogenesis
• Enzymology
• Membrane protein function

Background:

• Undecaprenyl phosphate (C55-P) is a vital lipid carrier for bacterial cell wall polymer synthesis.
• C55-P facilitates sugar transport across the plasma membrane for polymerization in the periplasm.
• The lipid carrier is released as undecaprenyl pyrophosphate (C55-PP), which requires dephosphorylation to C55-P for reuse.

Purpose of the Study:

• Investigate the roles of multiple phosphatases in C55-PP dephosphorylation and C55-P recycling.
• Elucidate the functional and structural characteristics of these essential enzymes.
• Understand the redundancy and specific functions of phosphatases like BacA, YbjG, LpxT, and PgpB in Escherichia coli.

Main Methods:

• Biochemical assays to characterize phosphatase activity.
• Genetic analysis, including gene inactivation studies.
• Structural biology techniques (e.g., X-ray crystallography) for apo- and halo-UppS structures.
• Subcellular localization studies of PAP2 enzymes.

Main Results:

• Four integral membrane proteins (BacA, YbjG, LpxT, PgpB) dephosphorylate C55-PP in E. coli.
• Simultaneous inactivation of bacA, ybjG, and pgpB leads to a lethal phenotype, indicating functional redundancy.
• LpxT specifically transfers a phosphate group from C55-PP to lipid A, forming lipid A 1-diphosphate.
• Active sites of LpxT, PgpB, and YbjG face the periplasm, suggesting their primary role in C55-PP recycling.

Conclusions:

• A redundant system of phosphatases ensures the efficient recycling of the undecaprenyl phosphate lipid carrier.
• PAP2 family members play crucial roles in maintaining the supply of C55-P for cell wall synthesis.
• LpxT has a dual role, participating in both C55-PP dephosphorylation and lipopolysaccharide modification.