phaG encodes a PhaG-family acyltransferase that connects de novo fatty-acid synthesis to medium-chain-length polyhydroxyalkanoate (mcl-PHA) biosynthesis by routing ACP-bound (R)-3-hydroxyacyl intermediates toward PHA monomer supply. Purified PhaG transfers a 3-hydroxydecanoyl group between CoA and ACP in vitro, but the directionality and exact in vivo mechanism (direct ACP:CoA transacylation versus thioester hydrolysis coupled to an acyl-CoA ligase) remain debated. Deletion genetics in KT2440 show that PhaG is a contributory but non-essential, partially redundant node in monomer supply.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0042621 poly(3-hydroxyalkanoate) biosynthetic process | IMP PMID:9727022 A new metabolic link between fatty acid de novo synthesis an... | NEW | Summary: PhaG should be connected to poly(3-hydroxyalkanoate) biosynthesis. It acts on ACP-bound de novo fatty-acid-synthesis intermediates and is the originally described "metabolic link" between fatty acid de novo synthesis and PHA accumulation, although the precise route to the CoA-activated PhaC substrate remains unresolved. Deletion reduces but does not abolish PHA, so this involvement is genuine but contributory. Reason: Complementation in KT2440 directly linked phaG to PHA synthesis from gluconate, while the reviewed UniProt entry independently places PhaG in polyhydroxyalkanoate biosynthesis. PhaG is contributory rather than indispensable because alternative monomer-supply routes remain available. Supporting Evidence: PMID:9727022 phenotypic complementation of these mutants file:PSEPK/phaG/phaG-uniprot.txt PATHWAY: Polyester biosynthesis; polyhydroxyalkanoate biosynthesis file:PSEPK/phaG/phaG-uniprot.txt DR UniPathway; UPA00212 file:PSEPK/phaG/phaG-deep-research-falcon.md PhaG is consistently positioned as enabling flux from FAS to PHA precursors by acting on **ACP-bound (R)-3-hydroxyacyl** intermediates and supplying PHA monomers file:PSEPK/phaG/phaG-deep-research-falcon.md Additional **phaG deletion** caused a **further 1.8-fold decrease** in PHA content but **did not abolish** PHA accumulation |
| GO:0016747 acyltransferase activity, transferring groups other than amino-acyl groups | IDA PMID:9727022 A new metabolic link between fatty acid de novo synthesis an... | NEW | Summary: PhaG catalyzes transfer of a 3-hydroxydecanoyl acyl group between CoA and acyl carrier protein in vitro. Reason: GO lacks a PhaG-specific molecular-function term, but the demonstrated transfer of a non-amino-acyl 3-hydroxydecanoyl group supports GO:0016747 despite uncertainty about the dominant physiological direction and mechanism. Supporting Evidence: PMID:9727022 It catalyzes the transfer of the acyl moiety from in vitro synthesized 3-hydroxydecanoyl-CoA to acyl carrier protein, indicating that PhaG exhibits a 3-hydroxyacyl-CoA-acyl carrier protein transferase activity |
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Download this section (compressed HTML)Q: Is PhaG active on additional 3-hydroxyacyl chain lengths in KT2440, or is 3-hydroxydecanoyl the physiologically dominant donor?
Q: What is the dominant in vivo activity of KT2440 PhaG — direct ACP:CoA transacylation or thioesterase-mediated release of free 3-hydroxy fatty acids followed by acyl-CoA ligase (e.g., AlkK/PP_0763) activation — and does this differ between native KT2440 and heterologous hosts?
Experiment: Measure purified PhaG activity with a panel of 3-hydroxyacyl-ACP and 3-hydroxyacyl-CoA donors/acceptors to resolve directionality and chain-length specificity, and compare PHA monomer composition in a phaG knockout versus wild-type KT2440.
Type: enzyme substrate panel and PHA composition assay
Experiment: Reconstruct the FAS-to-PHA route in a thioesterase-minimized E. coli background with and without an acyl-CoA ligase to discriminate the transacylase versus thioesterase+ligase models for PhaG in vivo.
Type: heterologous pathway reconstruction with controlled thioesterase/ligase background
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