nicP (PP_3939) encodes a porin-like outer-membrane protein within the experimentally validated aerobic nicotinate (nicotinic acid, NA) degradation gene cluster of Pseudomonas putida KT2440 (cluster organization nicTPFEDCXRAB). Within this cluster nicP is annotated as a "potential porin" and nicT as a "permease", together forming the putative transport/access module that brings NA (or a related pathway metabolite) into the cell for the maleamate pathway. NicP belongs to the outer membrane porin (Opr; TC 1.B.25) family. Direct experimental characterization of NicP itself - substrate, transport kinetics, knockout phenotype, localization, or structure - has not been reported; its porin activity and outer-membrane localization are inferences from family/cluster context, and its specific transported substrate remains unproven.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0015288 porin activity | IEA GO_REF:0000120 | ACCEPT | Summary: Porin activity is appropriate for the porin-like NicP protein, consistent with its membership in the outer membrane porin (Opr) family and its annotation within the nic cluster as a "potential porin". Reason: UniProt names NicP as a porin-like protein and places it in the outer membrane porin (Opr; TC 1.B.25) family. Deep research confirms that within the experimentally validated KT2440 nic catabolic cluster, nicP is described as a "potential porin", consistent with a beta-barrel channel function. Note this remains an inference - NicP itself has not been assayed for transport - but porin activity is the best-supported molecular function term. Supporting Evidence: file:PSEPK/nicP/nicP-uniprot.txt Porin-like protein NicP file:PSEPK/nicP/nicP-uniprot.txt outer membrane porin file:PSEPK/nicP/nicP-deep-research-falcon.md nicP** is described as a **βpotential porinβ** and **nicT** as a **βpermeaseβ**, indicating a putative transport/access module for NA (or related compounds) into the cell |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: Generic membrane localization is correct but should be refined to cell outer membrane for this porin-like protein of a Gram-negative bacterium. Reason: NicP belongs to the outer membrane porin (Opr) family; GO:0009279 (cell outer membrane) is more specific than generic membrane for a Gram-negative bacterial porin. Deep research notes that a porin is an outer membrane beta-barrel and that the porin annotation implies an outer-membrane location, though no direct localization experiment for NicP was found, so this is an inference rather than experimentally demonstrated. Proposed replacements: cell outer membrane Supporting Evidence: file:PSEPK/nicP/nicP-uniprot.txt outer membrane porin file:PSEPK/nicP/nicP-deep-research-falcon.md A **porin** is typically an outer membrane Ξ²βbarrel protein forming a channel that facilitates diffusion of small molecules across the Gram-negative outer membrane |
| GO:0055085 transmembrane transport | IEA GO_REF:0000108 | ACCEPT | Summary: Transmembrane transport is the appropriate broad process for a porin. The substrate remains undefined, but the deep research supports a working role in importing nicotinate or a related pathway metabolite. Reason: Porin activity implies transport across a membrane. Deep research situates NicP within the nicTPFEDCXRAB transport/access module and proposes nicotinate (NA) uptake as the working hypothesis, though the specific substrate is unproven. Transmembrane transport is therefore the correct, suitably general process term; the more specific nicotinate catabolic process is added as a NEW biological-process annotation below. Supporting Evidence: file:PSEPK/nicP/nicP-uniprot.txt Probable transporter, possibly involved in the aerobic file:PSEPK/nicP/nicP-deep-research-falcon.md the common working hypothesis is that NicP participates in **NA (nicotinate) uptake** or uptake of a chemically related pathway substrate, but this remains **unproven** |
| GO:0009279 cell outer membrane | IC file:PSEPK/nicP/nicP-uniprot.txt | NEW | Summary: NicP should have a cell outer membrane location annotation, inferred from its porin activity and membership in the Gram-negative outer membrane porin (Opr) family. Reason: The current GOA fetch only has generic membrane, but UniProt identifies NicP as an outer membrane porin family protein; the inference is from the accepted porin activity annotation (GO:0015288) plus Gram-negative outer-membrane porin family context to cell outer membrane (GO:0009279). Deep research reinforces that a porin is an outer-membrane beta-barrel, while cautioning that no direct localization experiment for NicP was reported. Supporting Evidence: file:PSEPK/nicP/nicP-uniprot.txt outer membrane porin file:PSEPK/nicP/nicP-uniprot.txt Porin-like protein NicP |
| GO:1901848 nicotinate catabolic process | IC file:PSEPK/nicP/nicP-deep-research-falcon.md | NEW | Summary: NicP is a member of the experimentally validated KT2440 aerobic nicotinate degradation gene cluster and contributes to nicotinate catabolism by providing porin-mediated substrate access; a nicotinate catabolic process annotation captures this pathway role more specifically than generic transmembrane transport. Reason: Deep research establishes that nicP is part of the nicTPFEDCXRAB locus required for aerobic NA catabolism in KT2440 and is annotated as a potential porin within that locus, functioning as the cluster's transport/access module for nicotinate. GO:1901848 (nicotinate catabolic process) is the precise biological-process term for this pathway. IC is appropriate because the assignment is inferred from cluster membership and porin annotation rather than a direct nicP-specific assay. Supporting Evidence: file:PSEPK/nicP/nicP-deep-research-falcon.md NicP is part of the **nicTPFEDCXRAB** locus required for aerobic NA catabolism in KT2440, and is **annotated as a potential porin** within that locus file:PSEPK/nicP/nicP-deep-research-falcon.md nicP (PP_3939; UniProt Q88FY7) is best supported as a porin-like, transport-associated member of the KT2440 nicotinate degradation cluster**, likely contributing to substrate access for NA catabolism |
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Download this section (compressed HTML)Q: Does NicP transport nicotinate, 6-hydroxynicotinate, or another nicotinate-pathway intermediate?
Experiment: Measure nicotinate and 6-hydroxynicotinate uptake in nicP mutant and complemented strains, and test purified NicP channel selectivity in reconstituted membranes.
Type: transport substrate specificity assay
Experiment: Determine NicP subcellular localization by outer-membrane fractionation and proteomics to experimentally confirm the inferred outer-membrane localization.
Type: subcellular localization assay
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