ahcY (PP_4976) encodes an NAD-dependent adenosylhomocysteinase that hydrolyzes S-adenosyl-L-homocysteine (SAH) to L-homocysteine and adenosine. The enzyme clears the inhibitory product of SAM-dependent methyltransferases and supplies homocysteine for remethylation, thereby linking transmethylation to methionine regeneration in the bacterial methionine cycle.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004013 adenosylhomocysteinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Adenosylhomocysteinase activity is the core AhcY molecular function. Reason: UniProt assigns EC 3.13.2.1 and RHEA:21708 for hydrolysis of SAH to L-homocysteine and adenosine, exactly matching GO:0004013. Supporting Evidence: file:PSEPK/ahcY/ahcY-uniprot.txt Reaction=S-adenosyl-L-homocysteine + H2O = L-homocysteine + adenosine file:PSEPK/ahcY/ahcY-uniprot.txt Xref=Rhea:RHEA:21708 |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: Cytoplasmic localization is correct but broader than the existing cytosol annotation. Reason: UniProt explicitly supports cytoplasmic localization. The annotation is valid but redundant with the more specific cytosol annotation already present from an independent source, so it is retained as non-core rather than replaced by a duplicate GO:0005829 annotation. Supporting Evidence: file:PSEPK/ahcY/ahcY-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0005829 cytosol | IEA GO_REF:0000118 | ACCEPT | Summary: Cytosol is an appropriate specific location for soluble AhcY. Reason: The protein is annotated as cytoplasmic in UniProt and lacks targeting or membrane features; GO:0005829 captures the soluble cytoplasmic compartment. Supporting Evidence: file:PSEPK/ahcY/ahcY-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0033353 L-methionine cycle | IEA GO_REF:0000118 | ACCEPT | Summary: AhcY is a central SAH-clearing step in the L-methionine cycle. Reason: SAH hydrolysis connects SAM-dependent methylation to homocysteine remethylation. This is the direct AhcY implementation of the bacterial methionine cycle. Supporting Evidence: file:PSEPK/ahcY/ahcY-uniprot.txt May play a key role in the regulation of the intracellular |
| GO:0071269 L-homocysteine biosynthetic process | IEA GO_REF:0000104 | ACCEPT | Summary: AhcY directly produces L-homocysteine from SAH. Reason: UniProt assigns the enzyme to the single-step route from SAH to L-homocysteine, so the process annotation is chemically and pathway appropriate even though homocysteine is subsequently remethylated. Supporting Evidence: file:PSEPK/ahcY/ahcY-uniprot.txt L-homocysteine from S-adenosyl-L-homocysteine: step 1/1 |
| GO:0051287 NAD binding | ISS file:PSEPK/ahcY/ahcY-uniprot.txt | NEW | Summary: AhcY binds one NAD(+) cofactor per subunit. Reason: UniProt assigns a stoichiometric NAD(+) cofactor and multiple conserved NAD-contacting residues. NAD binding is therefore a supported non-core molecular function complementing the defining hydrolase activity. Supporting Evidence: file:PSEPK/ahcY/ahcY-uniprot.txt Name=NAD(+); Xref=ChEBI:CHEBI:57540 file:PSEPK/ahcY/ahcY-uniprot.txt Note=Binds 1 NAD(+) per subunit. |
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Download this section (compressed HTML)Q: Does AhcY abundance or activity determine the SAM:SAH ratio during high methylation demand in KT2440?
Experiment: Combine conditional ahcY depletion with targeted SAM, SAH, homocysteine, adenosine, and methionine measurements and global methylation readouts.
Type: conditional genetics and metabolomics
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