GO_REF:0000117

Electronic Gene Ontology annotations created by ARBA machine learning models.

ARBA supplies automated annotations that are useful but must be checked against direct gene evidence.

file:PSEPK/murU/murU-uniprot.txt

UniProtKB reviewed entry for murU

UniProt identifies murU as MurNAc-alpha-1-phosphate uridylyltransferase with EC 2.7.7.99 and peptidoglycan-recycling pathway placement.

GO_REF:0000041

Gene Ontology annotation based on UniPathway vocabulary mapping.

UniPathway mapping provides pathway annotations that should be retained only when the gene directly catalyzes or regulates that pathway step.

PMID:25767118

Crystal Structure of the N-Acetylmuramic Acid α-1-Phosphate (MurNAc-α1-P) Uridylyltransferase MurU, a Minimal Sugar Nucleotidyltransferase and Potential Drug Target Enzyme in Gram-negative Pathogens.

MurU structure and biochemistry support UTP, MurNAc-alpha-1-phosphate, and magnesium-dependent uridylyltransferase activity.

PMID:23831760

A cell wall recycling shortcut that bypasses peptidoglycan de novo biosynthesis.

A cell-wall recycling shortcut in P. putida uses AmgK and MurU to channel external MurNAc into peptidoglycan biosynthesis.

file:PSEPK/murU/murU-deep-research-falcon.md

Falcon deep research on murU (Edison Scientific Literature)

MurU is the MurNAc salvage/recycling uridylyltransferase that generates UDP-MurNAc, acting downstream of the anomeric MurNAc kinase AmgK in P. putida KT2440 (PP_0406).

"The UniProt target Q88QT2 is annotated as **MurU (murU; PP_0406)**, an **N-acetylmuramate α-1-phosphate uridylyltransferase** (EC 2.7.7.99) belonging to the **nucleotidyltransferase/MurU family** (GlmU-like NTP transferase fold). In the retrieved literature corpus, “MurU” is consistently used for the **MurNAc (N-acetylmuramic acid) salvage/recycling uridylyltransferase** that generates UDP-MurNAc downstream of an anomeric MurNAc kinase (AmgK)."
In vitro with the P. putida recycling enzymes, MurU acts after AmgK and converts MurNAc monophosphate intermediates into the corresponding UDP-MurNAc derivatives.

"Direct biochemical evidence in the retrieved corpus comes from work using the **P. putida cell-wall recycling enzymes AmgK and MurU** in vitro. In these experiments, MurU acts **after AmgK** (which generates a monophosphate MurNAc intermediate) and **converts MurNAc monophosphate intermediates into the corresponding UDP-sugars (UDP-MurNAc derivatives)**, as detected by high-resolution LC/MS."
MurU's product UDP-MurNAc is competent for entry into peptidoglycan precursor assembly, being accepted by downstream MurC-MurF ligases to make Park's nucleotide analogs.

"MurU’s product is functionally validated in the same experimental system because the resulting UDP-MurNAc derivatives were accepted by downstream **MurC–MurF** enzymes to generate Park’s nucleotide analogs, demonstrating that MurU’s product is competent for entry into PG precursor assembly."
MurU's physiological substrate is MurNAc-1P (generated by AmgK), though the enzyme tolerates several MurNAc substitutions, enabling bioorthogonal probe generation.

"**Interpretation for annotation:** MurU’s physiological substrate is MurNAc-1P (generated by AmgK from imported MurNAc/anhMurNAc-derived intermediates), but the enzyme exhibits practical tolerance for several substitutions on MurNAc, enabling probe generation."
The MurU salvage route provides an alternate path to UDP-MurNAc that bypasses the de novo MurA/MurB steps, relevant under fosfomycin-mediated MurA inhibition.

"The MurU salvage route is biologically important because it provides an **alternate route to UDP-MurNAc** that can **bypass dependence on the de novo MurA/MurB steps** under conditions where de novo synthesis is impaired (e.g., MurA inhibition by fosfomycin), a point emphasized in the labeling-and-rescue framework."
No direct localization experiment exists for P. putida MurU, but pathway context supports a cytosolic role generating the cytosolic precursor UDP-MurNAc for Mur ligases.

"However, pathway context strongly supports a **cytosolic localization**: Gram-negative PG fragments are described as being transported into the **cytoplasm** for recycling (e.g., via AmpG), and MurU generates **UDP-MurNAc**, which is a cytosolic precursor used by Mur ligases (MurC–MurF). Thus, MurU is best annotated as a **cytoplasmic enzyme** acting on MurNAc-phosphate intermediates arising from imported PG turnover products."