UndPP

UndPP, short for undecaprenyl pyrophosphate, is a lipid carrier molecule critical to bacterial cell wall biosynthesis. It is a C55 isoprenoid chain with a pyrophosphate group that anchors in the inner membrane, serving as a transient carrier for peptidoglycan precursors.

In the cell wall assembly process, Und-PP participates in forming lipid I and lipid II, which carry peptidoglycan subunits across the cytoplasmic membrane to the exterior side where they are incorporated into the growing cell wall. The cycle begins when UDP-N-acetylmuramyl-pentapeptide is transferred to Und-PP to form Lipid I; addition of N-acetylglucosamine yields Lipid II. After delivery of the disaccharide-pentapeptide, the precursor is polymerized into the peptidoglycan, and Und-PP is regenerated from Und-PP to Und-P (undecaprenyl phosphate) by specific phosphatases, enabling reuse of the carrier.

Biosynthesis of Und-PP is carried out by the enzyme undecaprenyl pyrophosphate synthase (UppS), which builds the C55 chain. Recycling involves phosphatases such as UppP (also known as BacA) that dephosphorylate Und-PP to Und-P. The Und-PP cycle is essential in many bacteria and is a target for antibiotics.

Clinical relevance includes antibiotics that disrupt Und-PP functioning, notably bacitracin, which binds Und-PP and prevents regeneration to Und-P. Resistance can arise through mutations in UppP/BacA or alterations in the regulatory pathways of cell wall synthesis.