pckA encodes ATP-dependent phosphoenolpyruvate carboxykinase (PEPCK, EC 4.1.1.49), a Mn2+-requiring enzyme that catalyzes the conversion of oxaloacetate (OAA) to phosphoenolpyruvate (PEP) with concomitant decarboxylation and ATP hydrolysis. This enzyme is a key control point in gluconeogenesis, enabling the synthesis of carbohydrates from TCA cycle intermediates. In methylotrophs, pckA plays a critical role in connecting the serine cycle to biosynthetic pathways: carbon from the serine cycle flows through glycolysis to pyruvate and the TCA cycle, and pckA enables the reverse flow from oxaloacetate back to PEP for biosynthesis of sugars and other metabolites. The enzyme functions in the cytoplasm and binds one Mn2+ ion per subunit, which is essential for catalysis. Unlike the GTP-dependent PEPCK found in many eukaryotes, bacterial pckA uses ATP as the phosphate donor. This enzymatic activity represents a crucial anaplerotic/cataplerotic node that allows the organism to balance carbon flow between energy production (glycolysis/TCA) and biosynthesis (gluconeogenesis) during methylotrophic growth. PckA is essential for growth on C1 compounds as it enables the regeneration of biosynthetic precursors from central metabolism.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000166 nucleotide binding | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: This is a very general parent term that is correct but not informative. The more specific terms GO:0005524 (ATP binding) and GO:0017076 (purine nucleotide binding) provide better functional annotation. |
| GO:0004611 phosphoenolpyruvate carboxykinase activity | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: This is a general term for PEPCK activity. However, the more specific term GO:0004612 (phosphoenolpyruvate carboxykinase (ATP) activity) properly distinguishes the ATP-dependent bacterial enzyme from the GTP-dependent eukaryotic form. |
| GO:0004612 phosphoenolpyruvate carboxykinase (ATP) activity | IEA GO_REF:0000120 | ACCEPT | Summary: This is the primary and specific catalytic activity of bacterial PckA - the ATP-dependent decarboxylation/phosphorylation of oxaloacetate to phosphoenolpyruvate. UniProt assigns EC 4.1.1.49 (the ATP-dependent enzyme), distinguishing it from the GTP-dependent eukaryotic form (EC 4.1.1.32). The falcon deep-research review confirms this reaction chemistry and its central role in M. extorquens AM1 carbon metabolism, including in vivo fluxomic and Ξpck genetic evidence. Supporting Evidence: file:METEA/pckA/pckA-uniprot.txt oxaloacetate + ATP = phosphoenolpyruvate + ADP + CO2 file:METEA/pckA/pckA-deep-research-falcon.md ATP-dependent PEPCK catalyzes the reversible interconversion between oxaloacetate (OAA) and phosphoenolpyruvate (PEP) |
| GO:0005524 ATP binding | IEA GO_REF:0000120 | ACCEPT | Summary: PckA uses ATP as the phosphate donor for converting oxaloacetate to PEP; UniProt annotates multiple ATP-binding-site residues. ATP binding is essential for the enzymatic activity. The falcon review notes the mechanism proceeds via OAA decarboxylation to a stabilized enolate followed by phosphoryl transfer from the nucleotide. Supporting Evidence: file:METEA/pckA/pckA-uniprot.txt oxaloacetate + ATP = phosphoenolpyruvate + ADP + CO2 file:METEA/pckA/pckA-deep-research-falcon.md catalysis proceeds stepwise via OAA decarboxylation to a stabilized enolate intermediate, enabling phosphoryl transfer from the nucleotide |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: This is a general parent term of cytosol. While correct, the more specific term GO:0005829 (cytosol) provides better localization information. |
| GO:0005829 cytosol | IEA GO_REF:0000118 | ACCEPT | Summary: PckA is a soluble central-carbon metabolic enzyme localized to the cytosol, where it functions at the PEP-pyruvate-OAA node. UniProt annotates the cytoplasm; the falcon review notes no AM1-specific localization experiment exists but treats PEPCK as a cytosolic central-metabolism enzyme as a general principle, consistent with this annotation. Supporting Evidence: file:METEA/pckA/pckA-uniprot.txt Cytoplasm |
| GO:0006094 gluconeogenesis | IEA GO_REF:0000120 | ACCEPT | Summary: PckA catalyzes the gluconeogenic (OAA -> PEP) step, converting the TCA-cycle/anaplerotic intermediate oxaloacetate to PEP for biosynthesis. In M. extorquens AM1 this is a C4->C3 interconversion at the PEP-pyruvate-OAA node, linking the serine cycle, ethylmalonyl-CoA pathway, and TCA cycle. Genome-scale reconstruction and 13C-fluxomics show net PEPCK flux (OAA->PEP) during methylotrophic growth, and Ξpck mutants have reduced biomass yield - supporting the gluconeogenesis/biosynthetic-precursor role. Supporting Evidence: file:METEA/pckA/pckA-uniprot.txt Carbohydrate biosynthesis; gluconeogenesis file:METEA/pckA/pckA-deep-research-falcon.md at branching points connecting the serine cycle, the ethylmalonyl-CoA pathway (EMCP), the TCA cycle, and anaplerotic processes file:METEA/pckA/pckA-deep-research-falcon.md supports a model in which AM1 uses PEPCK substantially as an **OAA β PEP (C4βC3)** route under at least some methylotrophic conditions. |
| GO:0016829 lyase activity | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: This is a general parent term for enzymes that catalyze cleavage reactions. While technically correct (PckA is a carboxy-lyase), the more specific term GO:0016831 provides better annotation. |
| GO:0016831 carboxy-lyase activity | IEA GO_REF:0000043 | ACCEPT | Summary: This accurately describes the enzymatic mechanism - PckA catalyzes the decarboxylation (carboxy-lyase activity) of oxaloacetate with concomitant phosphorylation to form PEP, releasing CO2 as a product. The falcon review describes the stepwise mechanism (OAA decarboxylation to a stabilized enolate intermediate before phosphoryl transfer), supporting the carboxy-lyase characterization. Supporting Evidence: file:METEA/pckA/pckA-uniprot.txt oxaloacetate + ATP = phosphoenolpyruvate + ADP + CO2 file:METEA/pckA/pckA-deep-research-falcon.md catalysis proceeds stepwise via OAA decarboxylation to a stabilized enolate intermediate, enabling phosphoryl transfer from the nucleotide |
| GO:0017076 purine nucleotide binding | IEA GO_REF:0000002 | ACCEPT | Summary: PckA binds ATP (a purine nucleotide) as a substrate for the phosphorylation reaction. This is a valid supporting molecular function, though GO:0005524 (ATP binding) is more specific. |
| GO:0046872 metal ion binding | IEA GO_REF:0000043 | ACCEPT | Summary: This is a general parent term. PckA specifically requires Mn2+ for catalysis (binds 1 Mn2+ ion per subunit). A more specific manganese ion binding term would be more informative, but this general term is correct. [file:METEA/pckA/pckA-uniprot.txt, "Binds 1 Mn(2+) ion per subunit"] |
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