PATB1 (Patatin-B1, UniProt P15476) is a member of the patatin glycoprotein family and one of the canonical potato (Solanum tuberosum) tuber patatins. It is a dual-function protein. First, it is the major soluble STORAGE protein of the potato tuber: patatin accounts for up to ~40% of total soluble tuber protein in mature/larger tubers and is widely interpreted as a nitrogen/carbon reserve. Second, it is a lipid acyl hydrolase (LAH) / phospholipase A-like serine hydrolase of the patatin (PNPLA) domain family, with broad deacylation activity toward glycerolipids - phospholipids (mono- and diacylphospholipids), galactolipids/galactosyl diglycerides and neutral mono- and diglycerides - plus measurable esterase activity on model chromogenic substrates. PATB1 is synthesized as a precursor with an N-terminal 23-residue signal peptide, is N-glycosylated, and is trafficked through the endomembrane system to be deposited in the vacuoles of tuber parenchyma cells; immunocytochemistry localizes patatin mainly to vacuoles and not to the apoplast/cell wall, consistent with the need to sequester a membrane-active lipid hydrolase away from cellular membranes. The patatin catalytic architecture is a Ca2+-independent serine hydrolase with a Ser-Asp dyad (PROSITE PNPLA domain; GXSXG nucleophile-elbow motif with the catalytic Ser77, and the DGA/G Asp215 proton acceptor) and a GGXR oxyanion hole. A defense/host-resistance role has been proposed (UniProt assigns the keywords "Plant defense" and notes the protein is "involved in host resistance"), but this role is INDIRECT: patatin LAH activity releases free fatty acids and lysolipids from membrane glycerolipids, supplying precursors for suberin/wax synthesis and generating antifungal/anti-insect fatty acids (e.g. against corn rootworm larvae and Phytophthora infestans). The defense interpretations are largely derived from broad patatin-family functional studies and mixed-isoform preparations rather than from PATB1-specific in planta pathogen experiments [file:SOLTU/PATB1/PATB1-deep-research-falcon.md; file:SOLTU/PATB1/PATB1-uniprot.txt].
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005773 vacuole | IEA GO_REF:0000044 | ACCEPT | Summary: IEA cellular-component annotation from the UniProt Swiss-Prot subcellular-location mapping (keyword "Vacuole"). Patatin is a vacuolar tuber protein, directly established by immunocytochemistry. Reason: Correct and strongly supported. The UniProt entry records SUBCELLULAR LOCATION: Vacuole, and primary immunocytochemistry (electron microscopy with protein-specific antibodies) localized patatin mainly to the vacuoles of tuber and induced leaf cells, with no detectable patatin in cell walls or intercellular spaces; esterase histochemistry co-localizes with patatin-containing parenchyma. Vacuolar compartmentation is the biologically meaningful location for a membrane-active LAH, sequestering it from cellular membranes. The term is at the appropriate level of specificity. Supporting Evidence: file:SOLTU/PATB1/PATB1-uniprot.txt SUBCELLULAR LOCATION: Vacuole file:SOLTU/PATB1/PATB1-deep-research-falcon.md Experimental immunocytochemistry localizes patatin predominantly to vacuoles (not apoplast), consistent with the need to sequester a membrane-active lipid hydrolase away from cellular membranes. file:SOLTU/PATB1/PATB1-deep-research-falcon.md Histochemical staining for esterase activity in tuber sections showed activity restricted to parenchyma cells, consistent with the tissue distribution of patatin. |
| GO:0006629 lipid metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: IEA biological-process annotation from InterPro (IPR002641, PNPLA domain). The essence is correct - patatin is a lipid-acting enzyme - but "lipid metabolic process" is the broad parent of the specific lipid-DEGRADATION process that patatin catalyzes. Reason: Patatin is a lipid acyl hydrolase: its activity is deacylation/breakdown of glycerolipids (release of free fatty acids and lysolipids), which is lipid CATABOLISM rather than generic lipid metabolism. The deep research describes patatin LAH activity as releasing fatty acids from polar and neutral glycerolipids, and UniProt assigns the keywords "Lipid degradation" and "Lipid metabolism". The hydrolytic, degradative direction is well established, so the more specific child term "lipid catabolic process" (GO:0016042) is the accurate process annotation - and it is exactly the term that the retired SPKW annotation (re-added below) used. Modifying the generic IEA up to the catabolic child consolidates the process annotation at the correct specificity. Proposed replacements: lipid catabolic process Supporting Evidence: file:SOLTU/PATB1/PATB1-deep-research-falcon.md Patatin/LAH activity releases fatty acids from glycerolipids (polar and neutral), generating **free fatty acids and lysolipids** file:SOLTU/PATB1/PATB1-deep-research-falcon.md The substrate range includes **mono- and diacylphospholipids, galactosyl diglycerides, mono- and diglycerides**. file:SOLTU/PATB1/PATB1-uniprot.txt Probable lipolytic acyl hydrolase (LAH), an activity which is |
| GO:0016298 lipase activity | IEA GO_REF:0000117 | MODIFY | Summary: IEA molecular-function annotation from an ARBA machine-learning model. Patatin is genuinely a lipid-hydrolyzing enzyme, but "lipase activity" is a broad parent; the patatin enzyme is more precisely a glycerophospholipase / phospholipase A-like acyl hydrolase. Reason: The core molecular function of patatin is well documented as a lipid acyl hydrolase (LAH) with phospholipase A-like behaviour: it hydrolyzes glycerophospholipids (mono- and diacylphospholipids) as well as galactolipids and neutral glycerolipids, acting at the sn-1 and sn-2 acyl positions in a Ca2+-independent manner via a Ser-Asp catalytic dyad. UniProt's IBA annotations for this protein already include "phospholipase activity" (GO:0004620). The generic "lipase activity" should be MODIFIED to the more informative "glycerophospholipase activity" (GO:0004620), which captures the documented phospholipid-deacylation function while remaining defensible given that PATB1-specific positional specificity (PLA1 vs PLA2) and kinetics are not uniquely resolved. (Note: PATB1 also acts on neutral and galacto-lipids, so the broad LAH character is real; "glycerophospholipase activity" is chosen as the most specific single MF strongly supported by both the family biochemistry and the existing IBA call.) Proposed replacements: glycerophospholipase activity Supporting Evidence: file:SOLTU/PATB1/PATB1-uniprot.txt Probable lipolytic acyl hydrolase (LAH), an activity which is file:SOLTU/PATB1/PATB1-deep-research-falcon.md the most defensible annotation here is a file:SOLTU/PATB1/PATB1-deep-research-falcon.md broad acyl-hydrolase / PLA-like file:SOLTU/PATB1/PATB1-deep-research-falcon.md The substrate range includes **mono- and diacylphospholipids, galactosyl diglycerides, mono- and diglycerides**. |
| GO:0045735 nutrient reservoir activity | IEA GO_REF:0000043 | ACCEPT | Summary: SPKW (GO_REF:0000043) annotation derived from the UniProt keyword "Storage protein"; snapshot-only, removed in the current GOA release. Patatin is THE major potato tuber storage protein (~40% of soluble tuber protein), so this is a correct and CORE molecular function. Reason: GOA's removal of this annotation was NOT justified - it was collateral damage from retiring the keyword pipeline, and it removed the single term capturing patatin's best-established biological role. Patatin is repeatedly described as the major soluble storage protein of potato tubers, accounting for up to ~40% of soluble tuber protein in larger tubers, and UniProt explicitly states patatin has "a dual role as a somatic storage protein and as an enzyme involved in host resistance" with the keyword "Storage protein". Critically, the current (2026) GOA release contains NO storage / nutrient-reservoir function term for PATB1 at all - the only molecular functions left are lipase/lipid-hydrolase terms - so removal of this SPKW annotation left the gene with no representation of its dominant tuber function. "Nutrient reservoir activity" (GO:0045735) should be re-asserted and treated as a core function. (This is the mixed-verdict storage arm: removal not justified; Tier C.) Supporting Evidence: file:SOLTU/PATB1/PATB1-uniprot.txt Patatin have a dual role as a somatic storage protein file:SOLTU/PATB1/PATB1-uniprot.txt represents approximately 40% of the total protein in mature tubers. file:SOLTU/PATB1/PATB1-deep-research-falcon.md Patatin is the **major soluble storage protein** of potato tubers and is widely interpreted as a **nitrogen/carbon reserve protein** in addition to its enzymatic activities. file:SOLTU/PATB1/PATB1-deep-research-falcon.md patatin levels scale with tuber size and that patatin forms about **40%** of total soluble protein in larger tubers |
| GO:0006952 defense response | IEA GO_REF:0000043 | MARK AS OVER ANNOTATED | Summary: SPKW (GO_REF:0000043) annotation derived from the UniProt keyword "Plant defense"; snapshot-only, removed in the current GOA release. Patatin's defense role is INDIRECT - mediated through its LAH enzymatic activity releasing antifungal/antinematode free fatty acids - so a direct biological-process "defense response" annotation over-states the evidence. Reason: GOA's removal of this annotation was JUSTIFIED. Patatin does not act as a defense effector in its own right; rather, its proposed defense/host-resistance contribution is a downstream consequence of its lipid acyl hydrolase activity, which releases free fatty acids and lysolipids that can be antimicrobial/anti-insect and can supply suberin/wax precursors. UniProt itself hedges, describing the LAH as "an activity which is thought to be involved in the response of tubers to pathogens" and patatin as "an enzyme involved in host resistance" - i.e. resistance is enacted via the enzyme, not via a dedicated defense-response program. The deep research is explicit that the defense interpretations are largely inferred from broad patatin-family studies and mixed-isoform preparations rather than from direct PATB1 pathogen experiments, and that the strongest direct PATB1 evidence is its localization and enzymatic capacity. A blanket process term "defense response" (GO:0006952) is therefore an over-annotation; the genuine biology is better captured by the molecular-function (glycerophospholipase / LAH) and lipid-catabolic-process terms. (This is the over-annotated arm: removal justified; Tier A.) Supporting Evidence: file:SOLTU/PATB1/PATB1-uniprot.txt thought to be involved in the response of tubers to pathogens. file:SOLTU/PATB1/PATB1-uniprot.txt as an enzyme involved in host resistance. This tuber protein file:SOLTU/PATB1/PATB1-deep-research-falcon.md patatin-mediated fatty-acid release may contribute to wound responses (e.g., suberin/wax precursor supply) and inhibit pests/pathogens. file:SOLTU/PATB1/PATB1-deep-research-falcon.md these defense roles are plausible but often derived from broader patatin-family functional studies or mixed-isoform preparations; the strongest direct evidence for PATB1 remains its localization and enzymatic capacity. |
| GO:0016042 lipid catabolic process | IEA GO_REF:0000043 | ACCEPT | Summary: SPKW (GO_REF:0000043) annotation derived from the UniProt keyword "Lipid degradation"; snapshot-only, removed in the current GOA release. Patatin's LAH activity hydrolyzes (deacylates) glycerolipids, so lipid catabolism is a correct and appropriately specific process term. Reason: GOA's removal of this annotation was NOT justified (or, at minimum, low-cost and undesirable). Patatin is a lipid acyl hydrolase that breaks down glycerolipids - releasing free fatty acids and lysolipids from mono- and diacylphospholipids, galactosyl diglycerides and neutral mono-/di-glycerides - which is precisely lipid catabolism. UniProt assigns the keyword "Lipid degradation" and the FUNCTION line "Probable lipolytic acyl hydrolase (LAH)". "Lipid catabolic process" (GO:0016042) is more specific and more accurate than the generic "lipid metabolic process" (GO:0006629) currently retained from InterPro; indeed the current GOA "lipid metabolic process" annotation is recommended above to be MODIFIED up to this catabolic child. Re-asserting the catabolic process term restores the correct process specificity. (This is the lipid-catabolic arm of the mixed verdict: removal not justified; Tier C.) Supporting Evidence: file:SOLTU/PATB1/PATB1-uniprot.txt Probable lipolytic acyl hydrolase (LAH), an activity which is file:SOLTU/PATB1/PATB1-deep-research-falcon.md Patatin/LAH activity releases fatty acids from glycerolipids (polar and neutral), generating **free fatty acids and lysolipids** file:SOLTU/PATB1/PATB1-deep-research-falcon.md The substrate range includes **mono- and diacylphospholipids, galactosyl diglycerides, mono- and diglycerides**. |
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Download this section (compressed HTML)Q: Does the PATB1 isoform specifically (as opposed to mixed-isoform patatin preparations) act as a phospholipase A1, A2 or B, and what are its kinetic constants and chain-position specificity on phospholipids versus galacto- and neutral lipids?
Suggested experts: P. R. Shewry
Q: Is the proposed defense/host-resistance role of PATB1 a direct in planta pathogen-resistance contribution, or solely a downstream consequence of free-fatty-acid release by its lipid acyl hydrolase activity?
Q: What is the relative metabolic importance of PATB1's storage (nitrogen/carbon reserve) function versus its lipid-hydrolase function during tuber dormancy, sprouting and wound/pathogen response?
Experiment: Express and purify recombinant PATB1 (P15476) alone and assay lipid acyl hydrolase activity against defined substrates - phosphatidylcholine and phosphatidylethanolamine (with sn-1 vs sn-2 positional reporters), monogalactosyl- and digalactosyl-diacylglycerol, and mono-/di-acylglycerols - to determine PATB1-specific substrate preference, positional specificity and kinetics.
Hypothesis: PATB1 is a broad-specificity, Ca2+-independent lipid acyl hydrolase that deacylates both phospholipids (at sn-1 and sn-2) and neutral/galacto-glycerolipids, consistent with patatin-family PLA-like behaviour.
Type: in vitro enzyme kinetics / substrate-specificity assay
Experiment: Generate PATB1-specific knockdown/knockout potato lines (e.g. RNAi or CRISPR targeting the class I patatin tuber gene) and challenge tubers with Phytophthora infestans and insect herbivores, measuring free-fatty-acid/oxylipin release and disease/pest outcomes alongside total tuber storage-protein content.
Hypothesis: Loss of PATB1 reduces tuber free-fatty-acid release upon wounding/infection and modestly impairs resistance, while substantially reducing tuber storage-protein content - dissociating the storage role from the indirect, enzyme-mediated defense role.
Type: reverse-genetics / pathogen-and-pest challenge
Experiment: Use catalytic-site mutants (Ser77Ala nucleophile; Asp215 proton acceptor) of PATB1 expressed in tubers to separate the storage (nutrient-reservoir) function from the lipid-hydrolase function, and assess whether storage accumulation is independent of catalytic activity.
Hypothesis: The storage/nutrient-reservoir function of PATB1 is independent of its catalytic LAH activity, so catalytically dead PATB1 still accumulates as a tuber reserve protein but abolishes lipid catabolism and the indirect defense contribution.
Type: structure-function / site-directed mutagenesis in planta
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