The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
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). (richter2026peptidoglycanrecyclingis pages 3-4, liang2018…labelingof pages 63-69)
Gram-negative bacteria remodel peptidoglycan (PG) continuously, releasing fragments (muropeptides) that can be imported and recycled; this recycling contributes to cell-wall homeostasis and can impact antibiotic responses. A common framework described in recent pathway-level work is: lytic enzymes release 1,6-anhydro-muropeptides, which are imported into the cytoplasm (often via AmpG), where sugar and peptide moieties are processed and re-enter precursor biosynthesis. (richter2026peptidoglycanrecyclingis pages 3-4)
Within this broader recycling landscape, some organisms (classically discussed for Pseudomonas spp.) use a MurU-dependent salvage route to channel MurNAc-derived intermediates back to UDP-MurNAc, rather than routing them through the MurQ etherase pathway that converts MurNAc-6P to GlcNAc-6P. This MurU route is often termed a “MurU shunt/shortcut” in the recycling literature. (richter2026peptidoglycanrecyclingis pages 3-4, richter2026peptidoglycanrecyclingis pages 4-5)
MurU is a uridylyltransferase that converts a MurNAc-phosphate (MurNAc-1P) intermediate into UDP-MurNAc, thereby regenerating the UDP-activated MurNAc precursor that feeds the canonical cytosolic Mur ligase steps (MurC–MurF) toward Park’s nucleotide and ultimately Lipid II. (liang2018…labelingof pages 63-69, liang2018…labelingof pages 10-14)
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. (liang2018…labelingof pages 63-69)
Although the text provided does not spell out the full stoichiometry, the standard biochemical interpretation consistent with the evidence is:
- MurNAc-α-1-phosphate + UTP → UDP-MurNAc + PPi
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. (liang2018…labelingof pages 57-63, liang2018…labelingof pages 63-69)
A key feature relevant to functional annotation is that the P. putida AmgK/MurU pair is promiscuous toward a panel of MurNAc analogs used for chemical biology. After AmgK phosphorylation, MurU converted monophosphate intermediates “1–8” to their respective UDP products by HRLC/MS; several intermediates (1, 3–5) were reportedly produced in >10 mg quantities and isolated for NMR characterization, implying robust acceptance by the enzymatic system. (liang2018…labelingof pages 63-69)
The substrate panel included MurNAc derivatives bearing bioorthogonal handles (e.g., azide/alkyne) and other functional groups; however, not all bulky derivatives were compatible across steps (e.g., some larger tags were not converted by MurU in the summarized table). (liang2018…labelingof pages 57-63, liang2018…labelingof pages 63-69)
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. (liang2018…labelingof pages 63-69)
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. (liang2018…labelingof pages 10-14, liang2018…labelingof pages 75-79)
No direct subcellular localization experiment (e.g., fractionation, tagging microscopy) for P. putida KT2440 MurU was present in the retrieved text.
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. (richter2026peptidoglycanrecyclingis pages 3-4, liang2018…labelingof pages 10-14)
A 2024 Methods in Molecular Biology chapter provides updated protocols and framing for exploiting AmgK + MurU as a MurNAc salvage module enabling bioorthogonal labeling of bacterial peptidoglycan using azido-MurNAc probes and click chemistry, including verification by mass spectrometry and microscopy workflows. Although the chapter’s primary organism is Tannerella forsythia, it explicitly defines MurU as NAM α-1-phosphate uridylyltransferase acting with AmgK in the salvage pathway and highlights the broader applicability of this enzymatic module as a tool for PG labeling and trafficking studies. Publication date: 2024 (final form available in PMC 2024-10-28). URL/DOI: https://doi.org/10.1007/978-1-0716-3491-2_1. (hyland2024bioorthogonallabelingand pages 1-3)
A 2023 study in Frontiers in Cellular and Infection Microbiology investigated deletions in PG recycling enzymes (AmpD, AnmK) in Acinetobacter baumannii and reported measurable impacts on phenotypes including biofilm formation and twitching motility (reported reductions ~76–78% in twitching in both mutants), along with broader discussion linking recycling pathway disruption to physiology and intrinsic fosfomycin resistance. While not MurU-specific and not in P. putida, this represents current (2023) experimental evidence that perturbing PG recycling enzymes can influence bacterial fitness/virulence traits—supporting the view that recycling pathways (including MurU shunts where present) are physiologically consequential and potential intervention points. Publication date: 2023-01. URL/DOI: https://doi.org/10.3389/fcimb.2022.1064053. (tajuelo2023roleofpeptidoglycan pages 7-9)
The P. putida AmgK/MurU salvage enzymes have been used as an enabling technology for metabolic labeling of the PG carbohydrate core. The approach described in the retrieved corpus uses the ability of AmgK/MurU to produce UDP-MurNAc (and UDP-MurNAc analogs) from exogenous MurNAc derivatives, which then feed into the normal biosynthetic machinery (MurC–MurF) and ultimately into PG. In engineered E. coli contexts expressing P. putida amgK/murU, supplementation with modified MurNAc sugars coupled with click chemistry permits fluorescence-based visualization of PG, including structured illumination microscopy (SIM) workflows and downstream applications (e.g., generation of labeled PG fragments). (liang2018…labelingof pages 10-14, liang2018…labelingof pages 75-79)
The MurU salvage route is conceptually important in antibiotic biology because it can provide a route to maintain UDP-MurNAc supply when MurA is inhibited by fosfomycin, motivating combination strategies that target recycling as a way to prevent bypass. In the retrieved experimental framework, engineered bacteria could sustain growth under fosfomycin when provided MurNAc analogs and the AmgK/MurU pathway. (liang2018…labelingof pages 75-79)
Kinetic characterization in the retrieved corpus reports for AmgK (the upstream kinase paired with MurU) with MurNAc:
- apparent Km = 30.41 ± 5.75 μM
- kcat = 6.58 ± 0.21 s⁻1
It further reports that for 2Az-NAM and 2Alk-NAM, AmgK shows ~10-fold lower catalytic efficiency than for MurNAc, with other bulky derivatives being ~100-fold less efficient. These kinetic values support the plausibility of substantial metabolic flux through the AmgK→MurU salvage module when native MurNAc is available, and also quantify the tradeoffs for probe analogs. (liang2018…labelingof pages 63-69)
In a cell-based assay (engineered E. coli ΔmurQ expressing P. putida AmgK/MurU), growth under 200 μg/mL fosfomycin could be restored by supplementation with 0.2% (w/v) MurNAc derivatives (including 2Az-NAM and 2Alk-NAM). This provides functional evidence that the salvage module can supply sufficient UDP-MurNAc equivalents to sustain PG synthesis and cell growth under MurA inhibition—an experimentally grounded demonstration of pathway capacity. (liang2018…labelingof pages 75-79)
In A. baumannii, deletion of recycling enzymes AmpD or AnmK led to large decreases in twitching motility (reported ~78% and ~76% reduction, respectively) under the study’s conditions, demonstrating that recycling pathway components can strongly influence surface-associated behaviors. (tajuelo2023roleofpeptidoglycan pages 7-9)
Across the retrieved sources, authors consistently frame MurU as a key node connecting cell wall turnover to precursor re-synthesis, and highlight two major implications:
1) Physiology and antibiotic response: recycling pathways can buffer or bypass inhibition of de novo steps (e.g., MurA), implying that recycling contributes to intrinsic or conditional antibiotic tolerance/resistance mechanisms. (liang2018…labelingof pages 75-79, richter2026peptidoglycanrecyclingis pages 3-4)
2) Tool development: enzymatic promiscuity of AmgK/MurU enables chemical biology probes and imaging of PG dynamics in bacteria and potentially in host-associated contexts (e.g., generating fluorescently labeled PG for trafficking studies). (liang2018…labelingof pages 63-69, hyland2024bioorthogonallabelingand pages 1-3)
The following table consolidates the key evidence supporting the functional annotation and uses only statements supported by the retrieved corpus.
| Topic | Key findings | Evidence source (author/year/title) | Publication date | URL/DOI when available | Citation ID(s) |
|---|---|---|---|---|---|
| Identity | UniProt Q88QT2 corresponds to murU / PP_0406 in Pseudomonas putida KT2440 and is described as N-acetylmuramate alpha-1-phosphate uridylyltransferase; pathway literature consistently uses MurU for the MurNAc salvage/MurU shunt enzyme. | Richter et al. 2026, Peptidoglycan recycling is critical for cell division, cell wall integrity, and β-lactam resistance in Caulobacter crescentus; Hyland et al. 2024, Bioorthogonal Labeling and Click-Chemistry-Based Visualization of the Tannerella forsythia Cell Wall | 2026 Apr; 2024 Oct | https://doi.org/10.7554/eLife.109465 ; https://doi.org/10.1007/978-1-0716-3491-2_1 | (richter2026peptidoglycanrecyclingis pages 4-5, hyland2024bioorthogonallabelingand pages 1-3) |
| Enzymatic reaction | MurU acts downstream of AmgK and converts MurNAc monophosphate intermediates to UDP-MurNAc products, i.e. the uridylyltransferase step that regenerates UDP-MurNAc for PG precursor synthesis. | Liang 2018 thesis, …labeling of the carbohydrate core in bacterial peptidoglycan via the Pseudomonas putida cell wall recycling enzymes AmgK and MurU and its applications | 2018 | Not available in snippet; cites Nat Commun 2017 in thesis | (liang2018…labelingof pages 63-69, liang2018…labelingof pages 57-63) |
| Substrate specificity | Purified P. putida AmgK/MurU accepted natural NAM and several modified NAM derivatives. MurU converted monophosphate intermediates 1–8 to UDP products; Table 4 indicates MurU accepted substrates generated from 2-azido-, 2-alkyne-, ketone-, and some photo-crosslinking derivatives, but not all bulky probes (e.g., streptavidin-affinity probes). | Liang 2018 thesis, …labeling of the carbohydrate core in bacterial peptidoglycan via the Pseudomonas putida cell wall recycling enzymes AmgK and MurU and its applications | 2018 | Not available in snippet | (liang2018…labelingof pages 57-63, liang2018…labelingof pages 63-69) |
| Pathway role | MurU is part of a MurNAc salvage / peptidoglycan recycling shortcut that provides another route to UDP-MurNAc from NAM, bypassing de novo MurA/B-dependent synthesis. In Gram-negative recycling, muropeptides are typically imported by AmpG, processed in the cytoplasm, and in MurU-pathway organisms the MurNAc-derived intermediate is returned to UDP-MurNAc. | Liang 2018 thesis, Figure 1.4 description and chapter text; Richter et al. 2026 eLife background | 2018; 2026 Apr | https://doi.org/10.7554/eLife.109465 | (liang2018…labelingof pages 10-14, richter2026peptidoglycanrecyclingis pages 3-4) |
| Localization inference | No direct localization experiment for P. putida MurU was present in the snippets, but pathway context supports a cytosolic role: recycled muropeptides are transported into the cytoplasm via AmpG, then separated/processed, and MurU uses MurNAc-phosphate intermediates to generate UDP-MurNAc for the cytoplasmic precursor pathway. | Richter et al. 2026, Peptidoglycan recycling is critical…; Liang 2018 thesis pathway context | 2026 Apr; 2018 | https://doi.org/10.7554/eLife.109465 | (richter2026peptidoglycanrecyclingis pages 3-4, liang2018…labelingof pages 10-14) |
| Applications | The P. putida AmgK/MurU system was exploited to generate UDP-MurNAc probes and to enable metabolic labeling of bacterial peptidoglycan with azido/alkyne NAM analogs, supporting fluorescence imaging, SIM/STORM, macrophage interaction studies, and production of labeled PG fragments. Related methods papers use heterologous AmgK/MurU expression to label PG in other organisms. | Liang 2018 thesis; Hyland et al. 2024, Bioorthogonal Labeling and Click-Chemistry-Based Visualization of the Tannerella forsythia Cell Wall | 2018; 2024 Oct | https://doi.org/10.1007/978-1-0716-3491-2_1 | (liang2018…labelingof pages 10-14, liang2018…labelingof pages 75-79, hyland2024bioorthogonallabelingand pages 1-3) |
| Quantitative data | For the partner kinase AmgK in the same P. putida pathway, reported kinetics with NAM were Km = 30.41 ± 5.75 μM and kcat = 6.58 ± 0.21 s^-1; 2Az-NAM and 2Alk-NAM showed about 10-fold lower efficiency than NAM. In cell assays, 0.2% (w/v) NAM analogs restored growth of engineered E. coli under 200 μg/mL fosfomycin. These data support flux through the AmgK→MurU salvage route, though MurU-specific kinetics were not given in the snippets. | Liang 2018 thesis, kinetic and growth sections | 2018 | Not available in snippet | (liang2018…labelingof pages 63-69, liang2018…labelingof pages 75-79) |
| Phenotype/pathway context | Pathway perturbation phenotypes in other bacteria support biological importance of MurU-shunt recycling. In A. baumannii, disrupting recycling enzymes increased fosfomycin susceptibility and altered fitness/virulence traits; under the reported conditions morphology was unchanged, interpreted as de novo synthesis still supplying UDP-MurNAc. | Tajuelo et al. 2023, Role of peptidoglycan recycling enzymes AmpD and AnmK in Acinetobacter baumannii virulence features | 2023 Jan | https://doi.org/10.3389/fcimb.2022.1064053 | (tajuelo2023roleofpeptidoglycan pages 7-9) |
Table: This table summarizes the key evidence supporting functional annotation of MurU (Q88QT2/PP_0406) in Pseudomonas putida KT2440, including its enzymatic role, pathway placement, inferred localization, applications, and available quantitative support. It is restricted to findings present in the provided evidence snippets.
view_images was attempted for pathway figures (e.g., the PG biosynthesis schematic describing the AmgK/MurU route), but the tool could not retrieve images from the thesis text chunks; therefore, this report cannot include figure-cropped image citations despite the attempt.murU (Q88QT2; PP_0406) encodes a cytosolic N-acetylmuramate-α-1-phosphate uridylyltransferase (MurU; EC 2.7.7.99) that converts MurNAc-1-phosphate to UDP-MurNAc in the MurNAc salvage (MurU shunt) arm of peptidoglycan recycling, acting downstream of AmgK and upstream of MurC–MurF to regenerate PG precursors; the P. putida AmgK/MurU system shows experimentally demonstrated promiscuity toward several MurNAc analogs enabling metabolic labeling and probe generation. (liang2018…labelingof pages 63-69, liang2018…labelingof pages 10-14)
References
(richter2026peptidoglycanrecyclingis pages 3-4): Pia Richter, Anna Merz, Jacob Biboy, Nicole Paczia, Timo Glatter, Jared Ng, Waldemar Vollmer, and Martin Thanbichler. Peptidoglycan recycling is critical for cell division, cell wall integrity, and β-lactam resistance in caulobacter crescentus. eLife, Apr 2026. URL: https://doi.org/10.7554/elife.109465, doi:10.7554/elife.109465. This article has 1 citations and is from a domain leading peer-reviewed journal.
(liang2018…labelingof pages 63-69): H Liang. … labeling of the carbohydrate core in bacterial peptidoglycan via the pseudomonas putida cell wall recycling enzymes amgk and muru and its applications. Unknown journal, 2018.
(richter2026peptidoglycanrecyclingis pages 4-5): Pia Richter, Anna Merz, Jacob Biboy, Nicole Paczia, Timo Glatter, Jared Ng, Waldemar Vollmer, and Martin Thanbichler. Peptidoglycan recycling is critical for cell division, cell wall integrity, and β-lactam resistance in caulobacter crescentus. eLife, Apr 2026. URL: https://doi.org/10.7554/elife.109465, doi:10.7554/elife.109465. This article has 1 citations and is from a domain leading peer-reviewed journal.
(liang2018…labelingof pages 10-14): H Liang. … labeling of the carbohydrate core in bacterial peptidoglycan via the pseudomonas putida cell wall recycling enzymes amgk and muru and its applications. Unknown journal, 2018.
(liang2018…labelingof pages 57-63): H Liang. … labeling of the carbohydrate core in bacterial peptidoglycan via the pseudomonas putida cell wall recycling enzymes amgk and muru and its applications. Unknown journal, 2018.
(liang2018…labelingof pages 75-79): H Liang. … labeling of the carbohydrate core in bacterial peptidoglycan via the pseudomonas putida cell wall recycling enzymes amgk and muru and its applications. Unknown journal, 2018.
(hyland2024bioorthogonallabelingand pages 1-3): Stephen N. Hyland, Sreedevi Chinthamani, Sushanta Ratna, Kimberly A. Wodzanowski, Liam-Michael D. Sandles, Kiyonobu Honma, Catherine Leimkuhler-Grimes, and Ashu Sharma. Bioorthogonal labeling and click-chemistry-based visualization of the tannerella forsythia cell wall. Methods in molecular biology, 2727:1-16, Oct 2024. URL: https://doi.org/10.1007/978-1-0716-3491-2_1, doi:10.1007/978-1-0716-3491-2_1. This article has 3 citations and is from a peer-reviewed journal.
(tajuelo2023roleofpeptidoglycan pages 7-9): Ana Tajuelo, María C. Terrón, Mireia López-Siles, and Michael J. McConnell. Role of peptidoglycan recycling enzymes ampd and anmk in acinetobacter baumannii virulence features. Frontiers in Cellular and Infection Microbiology, Jan 2023. URL: https://doi.org/10.3389/fcimb.2022.1064053, doi:10.3389/fcimb.2022.1064053. This article has 12 citations.