TaTFP is a thiocyanate-forming protein of field pennycress, an iron(II)-dependent specifier protein in the glucosinolate-myrosinase chemical defense system. It is a Kelch-repeat, six-bladed beta-propeller protein that acts as a homodimer. Rather than hydrolyzing intact glucosinolates, it captures the unstable aglucone generated by myrosinase upon tissue damage and redirects its rearrangement away from the default isothiocyanate, catalyzing formation of organic thiocyanates (e.g. allylthiocyanate), epithionitriles, and simple nitriles. The protein is curated as a carbon-sulfur lyase (sulfolyase, EC 4.8.1.8) and is expressed constitutively across plant tissues.
The preferred accession for this review is G1FNI6. These relationships are manually assessed.
REFERENCE PROTEOME EQUIVALENT Β· Reviewed 2026-10-19
Reference proteome: UP000836841
Retain G1FNI6 as the primary Swiss-Prot accession. The leading reference sequence has 97.13% global identity, full target coverage and a short terminal difference, and is separated from other specifier-family hits. This supports a qualified sequence-based counterpart. Its generic epithiospecifier annotation does not independently establish thiocyanate-forming specificity, so functional annotation transfer still requires review.
MMseqs2 searched 26,379 sequences across UP000836841 at E <= 1e-5 and sensitivity 7.5, returning 28 hits. Every returned sequence was globally aligned using BLOSUM62 with gap-open -10 and extension -0.5. Scores and sequences for all 28 returned candidates are retained, with 10 detailed alignment files. The heuristic search does not establish genomic absence or unique locus identity.
file:THLAR/TFP/TFP-record-evidence.yaml
target_sequence_count: 26379
file:THLAR/TFP/TFP-record-evidence.yaml
candidate_count: 28
A0AAU9R9U8: 338 identities across 348 global-alignment columns (97.1264% identity including gaps), 2 substitutions and 8 gap columns. Query coverage is 97.7011%; target coverage is 100.0%. Sequence similarity is interpreted in the manual rationale. Identity over paired residues is 99.4118% (338/340); gap columns are excluded from this denominator.
file:THLAR/TFP/TFP-record-evidence.yaml
query_length: 348 target_length: 340 alignment_columns: 348 identities: 338 mismatches: 2 gap_columns: 8 identity_percent: 97.1264 query_coverage_percent: 97.7011 target_coverage_percent: 100.0
The primary accession is outside every searched exact-taxon reference proteome. Current UniProt records place A0AAU9R9U8 in UP000836841 and give it the same taxon as the primary.
file:THLAR/TFP/TFP-record-evidence.yaml
primary_in_any_reference_proteome: false
file:THLAR/TFP/TFP-record-evidence.yaml
alternative_in_reference_proteome: true
file:THLAR/TFP/TFP-record-evidence.yaml
same_taxon: true
Sampled UniSave observations: 11-NOV-2015, entry version 12.: no Proteomes cross-reference; 11-DEC-2019, entry version 25.: no Proteomes cross-reference; 27-NOV-2024, entry version 36.: no Proteomes cross-reference. These dated observations do not establish uninterrupted membership/absence, the exact change date, or UniProt's motivation.
file:THLAR/TFP/TFP-record-evidence.yaml
entry_date: 11-NOV-2015, entry version 12. proteomes: []
file:THLAR/TFP/TFP-record-evidence.yaml
entry_date: 11-DEC-2019, entry version 25. proteomes: []
file:THLAR/TFP/TFP-record-evidence.yaml
entry_date: 27-NOV-2024, entry version 36. proteomes: []
Definition: A carbon-sulfur lyase activity that eliminates sulfate from a glucosinolate aglucone to yield an organic thiocyanate (EC 4.8.1.8). No GO molecular-function term currently captures this specific specifier-protein activity; carbon-sulfur lyase activity (GO:0016846) is the closest available parent.
Justification: The reaction is curated in UniProt (EC 4.8.1.8) and structurally characterized, but the existing GO MF granularity stops at the carbon-sulfur lyase parent, leaving specifier-protein catalysis under-described.
Parent term: carbon-sulfur lyase activity
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005634 nucleus | IEA GO_REF:0000118 | UNDECIDED | Summary: The propagated nuclear localization of TaTFP is not resolved. Reason: Arabidopsis ESP has conditional WRKY53-dependent nuclear recruitment; that observation neither demonstrates nor excludes a nuclear pool of pennycress TFP. Direct TaTFP structural and coupled-enzyme evidence does not establish this compartment. Do not call the original localization disproven by the absence of a known nuclear role. |
| GO:0005829 cytosol | IEA GO_REF:0000118 | ACCEPT | Summary: Plausible and consistent with function. Specifier proteins act in the cytosol where myrosinase-released glucosinolate aglucones become available. Direct subcellular localization of TaTFP has not been experimentally established, but the cytosol is the expected site of action. Supporting Evidence: file:THLAR/TFP/TFP-deep-research-falcon.md broader glucosinolate-system reviews/localization studies discuss cytoplasmic organization for specifier proteins and compartmented myrosinases |
| GO:0019760 glucosinolate metabolic process | IEA GO_REF:0000117 | MODIFY | Summary: Correct, but the generic metabolic-process parent should be specialized to the catabolic child, consistent with the experimentally supported breakdown role of TaTFP downstream of myrosinase. Proposed replacements: glucosinolate catabolic process |
| GO:0030234 enzyme regulator activity | IEA GO_REF:0000118 | MODIFY | Summary: Outdated molecular-function framing. Specifier proteins were historically viewed as accessory factors that "regulate" myrosinase product outcome, but TaTFP is now established as a catalyst in its own right - an Fe(2+)-dependent carbon-sulfur lyase (sulfolyase, EC 4.8.1.8) that eliminates sulfate from the glucosinolate aglucone to form thiocyanates and nitriles. The activity should be captured as a lyase, not as enzyme regulator activity. [PMID:30900313 "specifier proteins act as Fe(2+)-dependent lyases"] Proposed replacements: carbon-sulfur lyase activity Supporting Evidence: PMID:30900313 Structural diversification during glucosinolate breakdown: mechanisms of thiocyanate, epithionitrile and simple nitrile formation PMID:21783213 A thiocyanate-forming protein generates multiple products upon allylglucosinolate breakdown in Thlaspi arvense. PMID:23999604 Molecular models and mutational analyses of plant specifier proteins suggest active site residues and reaction mechanism |
| GO:0080028 nitrile biosynthetic process | IEA GO_REF:0000118 | ACCEPT | Summary: Correct. TaTFP generates simple nitriles and epithionitriles (e.g. 3,4-epithiobutanenitrile) from glucosinolate aglucones, in addition to organic thiocyanates. [PMID:21783213; PMID:30900313] Supporting Evidence: PMID:21783213 A thiocyanate-forming protein generates multiple products upon allylglucosinolate breakdown in Thlaspi arvense. PMID:30900313 mechanisms of thiocyanate, epithionitrile and simple nitrile formation |
| GO:0019760 glucosinolate metabolic process | IDA PMID:26260516 The crystal structure of the thiocyanate-forming protein fro... | MODIFY | Summary: Experimentally supported but can be made more precise. TaTFP acts in the breakdown (catabolism) of glucosinolates downstream of myrosinase, so the catabolic child term is more informative than the generic metabolic-process parent. [PMID:26260516 "a kelch protein involved in glucosinolate breakdown"] Proposed replacements: glucosinolate catabolic process Supporting Evidence: PMID:26260516 The crystal structure of the thiocyanate-forming protein from Thlaspi arvense, a kelch protein involved in glucosinolate breakdown |
| GO:0042802 identical protein binding | IDA PMID:26260516 The crystal structure of the thiocyanate-forming protein fro... | KEEP AS NON CORE | Summary: Reflects the homodimeric quaternary state demonstrated in the crystal structure. Real but structural rather than the catalytic core function; retained as non-core. The homodimerization-activity annotation below is the more specific of the two. Supporting Evidence: PMID:26260516 crystal structure of the thiocyanate-forming protein from Thlaspi arvense |
| GO:0042803 protein homodimerization activity | IDA PMID:26260516 The crystal structure of the thiocyanate-forming protein fro... | KEEP AS NON CORE | Summary: Supported by the crystal structure, which shows TaTFP is a homodimer. A genuine structural property of the protein, retained as non-core relative to its catalytic lyase activity. [PMID:26260516] Supporting Evidence: PMID:26260516 TaTFP crystallized as homodimer. |
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Experiment: Determine TaTFP subcellular localization by fluorescent-protein fusion or immunolocalization in Thlaspi arvense, and test co-compartmentalization with myrosinase to define where aglucone capture occurs in vivo.
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