NicF is a maleamate amidohydrolase in the aerobic nicotinate degradation pathway of Pseudomonas putida KT2440. It converts maleamate into maleate and ammonium, acting after NicD deformylation and before MaiA/NicE maleate isomerization to fumarate. NicF belongs to the isochorismatase-like hydrolase family, with a predicted cysteine-centered catalytic mechanism.
Definition: Catalysis of the reaction maleamate + H2O = maleate + NH4(+).
Justification: The substrate-specific reaction is experimentally established, whereas the existing GO parent groups many unrelated linear-amide hydrolases. QuickGO exact-substrate searches did not recover a matching molecular function.
Parent term: hydrolase activity, acting on carbon-nitrogen (but not peptide) bonds, in linear amides
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:1901848 nicotinate catabolic process | IDA PMID:18678916 Deciphering the genetic determinants for aerobic nicotinic a... | ACCEPT | Summary: nicF directly performs a lower-pathway chemical step in nicotinate catabolism. Reason: Recombinant NicF cell extracts hydrolyzed maleamate with reported specific activity 19.3 micromol/min/mg. This directly establishes catalysis of a pathway step; the paper does not report an individual nicF knockout. The glutamate-dehydrogenase/NADPH coupling measures released ammonium and does not make NADPH a NicF cofactor. The primary full text was inspected externally; the local cache is abstract-only. Supporting Evidence: file:PSEPK/nicF/nicF-uniprot.txt Reaction=maleamate + H2O = maleate + NH4(+); |
| GO:0016811 hydrolase activity, acting on carbon-nitrogen (but not peptide) bonds, in linear amides | IDA PMID:18678916 Deciphering the genetic determinants for aerobic nicotinic a... | MODIFY | Summary: Refine the broad linear-amide hydrolase activity to the characterized substrate-specific reaction. Reason: The linear-amide hydrolase parent is correct but less specific than the demonstrated maleamate amidohydrolase activity. No exact current GO term was recovered; the replacement corresponds to the supported proposed term. Family/conserved-residue analysis suggests a cysteine amidase mechanism, but it is not target-specific mutational proof of every catalytic residue or direct evidence of metal independence. Proposed replacements: maleamate amidohydrolase activity Supporting Evidence: file:PSEPK/nicF/nicF-uniprot.txt Reaction=maleamate + H2O = maleate + NH4(+); |
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Download this section (compressed HTML)Q: Can an exact GO molecular-function term be added for maleamate amidohydrolase activity?
Experiment: Test the predicted catalytic residues and metal dependence using purified KT2440 NicF rather than transferring detailed mechanism from a homolog.
Type: enzyme kinetics and mutagenesis
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