AOP2 (ALKENYL HYDROXALKYL PRODUCING 2; At4g03060) is an Fe(II)- and 2-oxoglutarate-dependent dioxygenase (2-ODD) that catalyzes a side-chain modification in methionine-derived (aliphatic) glucosinolate biosynthesis, converting methylsulfinylalkyl glucosinolates into alkenyl glucosinolates (e.g. 3-methylsulfinylpropyl to allyl/2-propenyl glucosinolate, and 4-methylsulfinylbutyl glucoraphanin to 3-butenyl glucosinolate). It underlies the GS-ALK locus. AOP2 arose by tandem duplication with AOP3, which instead forms hydroxyalkyl glucosinolates, and the two are expressed in a mutually exclusive manner across accessions. This entry is the functional allele from the Cape Verde Islands (Cvi) accession (432 aa, AOP2-1); the Columbia allele carries a 5-bp deletion causing a frameshift and a non-functional truncated protein, so Col-0 accumulates methylsulfinylalkyl glucosinolates. AOP2 is expressed most strongly in leaves and stems in a light-dependent manner, and its activity shapes the glucosinolate profile and thus the isothiocyanate breakdown products that mediate defense against herbivores.
The preferred accession for this review is Q945B5. These relationships are manually assessed.
REFERENCE PROTEOME LOCUS COUNTERPART · Reviewed 2026-10-19
Reference proteome: UP000006548
Retain Q945B5 as the primary Swiss-Prot accession. UniProt explicitly identifies Q9ZTA2 as the Columbia AOP2 allele with a 5-bp deletion leading to a non-functional protein, contrasting the functional Cvi allele Q945B5. The observed sequence differences and length loss are consistent with that curated distinction. Record same-locus correspondence, not equivalent catalytic function.
MMseqs2 searched 39,272 sequences across UP000006548 at E <= 1e-5 and sensitivity 7.5, returning 106 hits. Every returned sequence was globally aligned using BLOSUM62 with gap-open -10 and extension -0.5. Scores and sequences for all 106 returned candidates are retained, with 10 detailed alignment files. The heuristic search does not establish genomic absence or unique locus identity.
file:ARATH/AOP2/AOP2-record-evidence.yaml
target_sequence_count: 39272
file:ARATH/AOP2/AOP2-record-evidence.yaml
candidate_count: 106
Q9ZTA2: 390 identities across 432 global-alignment columns (90.2778% identity including gaps), 9 substitutions and 33 gap columns. Query coverage is 92.3611%; target coverage is 100.0%. Sequence similarity is interpreted in the manual rationale. Identity over paired residues is 97.7444% (390/399); gap columns are excluded from this denominator.
file:ARATH/AOP2/AOP2-record-evidence.yaml
query_length: 432 target_length: 399 alignment_columns: 432 identities: 390 mismatches: 9 gap_columns: 33 identity_percent: 90.2778 query_coverage_percent: 92.3611 target_coverage_percent: 100.0
The primary accession is outside every searched exact-taxon reference proteome. Current UniProt records place Q9ZTA2 in UP000006548 and give it the same taxon as the primary.
file:ARATH/AOP2/AOP2-record-evidence.yaml
primary_in_any_reference_proteome: false
file:ARATH/AOP2/AOP2-record-evidence.yaml
alternative_in_reference_proteome: true
file:ARATH/AOP2/AOP2-record-evidence.yaml
same_taxon: true
Sampled UniSave observations: 24-JUN-2015, entry version 46.: no Proteomes cross-reference; 26-FEB-2020, entry version 59.: no Proteomes cross-reference; 27-NOV-2024, entry version 68.: no Proteomes cross-reference. These dated observations do not establish uninterrupted membership/absence, the exact change date, or UniProt's motivation.
file:ARATH/AOP2/AOP2-record-evidence.yaml
entry_date: 24-JUN-2015, entry version 46. proteomes: []
file:ARATH/AOP2/AOP2-record-evidence.yaml
entry_date: 26-FEB-2020, entry version 59. proteomes: []
file:ARATH/AOP2/AOP2-record-evidence.yaml
entry_date: 27-NOV-2024, entry version 68. proteomes: []
UniProt directly identifies the Columbia AOP2 deletion allele and the functional Cvi counterpart.
file:ARATH/AOP2/AOP2-record-evidence.yaml
5-bp deletion that leads to a non-functional protein
file:ARATH/AOP2/AOP2-record-evidence.yaml
functional and expressed alleles for AOP2 (AC Q945B5)
Definition: Catalysis of the Fe(II)- and 2-oxoglutarate-dependent conversion of an omega-(methylsulfinyl)alkyl glucosinolate to the corresponding omega-alkenyl glucosinolate with loss of the methylsulfinyl group, e.g. 3-methylsulfinylpropyl glucosinolate to allyl (2-propenyl) glucosinolate, or 4-methylsulfinylbutyl glucosinolate (glucoraphanin) to 3-butenyl glucosinolate (gluconapin).
Justification: AOP2 (GS-ALK) has a biochemically demonstrated, substrate-defined activity that determines alkenyl glucosinolate accumulation across Arabidopsis accessions and Brassica crops (BoGSL-ALK), but GO only offers the generic class term GO:0016706. The paralog AOP3 forms hydroxyalkyl glucosinolates from the same substrates, so a specific term would distinguish these neofunctionalized duplicates. Should be placed under 2-oxoglutarate-dependent dioxygenase activity (GO:0016706).
Parent term: 2-oxoglutarate-dependent dioxygenase activity
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016706 2-oxoglutarate-dependent dioxygenase activity | IDA PMID:11251105 Gene duplication in the diversification of secondary metabol... | ACCEPT | Summary: Heterologously expressed AOP2 (thioredoxin fusion in E. coli), assayed with 2-oxoglutarate and ascorbate, converted 3-methylsulfinylpropyl and 4-methylsulfinylbutyl glucosinolates to allyl and 3-butenyl glucosinolates. Reason: Correct and experimentally supported. GO has no specific term for the alkenyl glucosinolate-forming reaction, so the 2-oxoglutarate-dependent dioxygenase activity class term is the most specific existing MF term; a more precise new term is proposed (see proposed_new_terms). The assay included 2-oxoglutarate, and the protein contains the conserved Fe(II)/2OG-binding residues of the 2OG-FeII oxygenase domain. Supporting Evidence: PMID:11251105 induced AOP2 bacterial extracts catalyzed the conversion of the 3-methylsulfinylpropyl to the allyl glucosinolate and the 4-methylsulfinylbutyl to the 3-butenyl glucosinolate PMID:11251105 with the addition of 200 mM sucrose and the use of 10 mM oxoglutarate and 10 mM ascorbate instead of 40 mM of each of these |
| GO:0016706 2-oxoglutarate-dependent dioxygenase activity | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA machine-learning rule assigns 2-oxoglutarate-dependent dioxygenase activity based on the 2OG-FeII oxygenase domain. Reason: Consistent with the experimental IDA annotation and the domain architecture (DIOX_N and 2OG-FeII_Oxy Pfam domains; Fe-binding His/Asp and 2OG-binding Arg residues). Supporting Evidence: PMID:11251105 we report the identification of genes encoding two 2-oxoglutarate--dependent dioxygenases that are responsible for this variation |
| GO:0019761 glucosinolate biosynthetic process | IDA PMID:11251105 Gene duplication in the diversification of secondary metabol... | ACCEPT | Summary: AOP2 catalyzes the formation of alkenyl glucosinolates from methylsulfinylalkyl glucosinolate precursors, a secondary side-chain modification step of aliphatic glucosinolate biosynthesis. Reason: AOP2 directly catalyzes a biosynthetic step (enzyme assay), and in planta overexpression of a functional AOP2 allele in Col-0 converts methylsulfinylalkyl glucosinolates to 2-propenyl and 3-butenyl glucosinolates. Core process. Supporting Evidence: PMID:11251105 we show that AOP2 catalyzes the conversion of methylsulfinylalkyl glucosinolates to alkenyl glucosinolates PMID:20699011 The over-expression of a functional AOP2 allele was found to successfully convert the precursor methylsulfinyl alkyl glucosinolate into the alkenyl form. |
| GO:0019761 glucosinolate biosynthetic process | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA rule assigns glucosinolate biosynthetic process, consistent with the experimental evidence. Reason: Matches the experimentally established role of AOP2 in aliphatic glucosinolate side-chain modification. Supporting Evidence: PMID:20699011 In Arabidopsis the AOP2 gene plays a role in the secondary modification of aliphatic (methionine-derived) glucosinolates, namely the conversion of methylsulfinylalkyl glucosinolates to form alkenyl glucosinolates |
Loading supporting content…
Download this section (compressed HTML)Q: What is the chemical mechanism and by-product of AOP2-catalyzed alkenyl formation (loss of methanesulfenic acid?), and does AOP2 retain the canonical hydroxylation chemistry of 2-ODDs as a cryptic activity?
Q: Which active-site residues distinguish AOP2 (alkenyl-forming) from AOP3 (hydroxyalkyl-forming), given that the two arose by recent tandem duplication?
Q: AOP2 expression raises MYB28/MYB29 transcripts and alters jasmonate signaling independently of MYB28/MYB29 (PMID:25758208), and AOP2 alters flowering time in a background-dependent way (PMID:26442014). Are these effects mediated by alkenyl glucosinolates or their breakdown products, or by the AOP2 protein itself?
Experiment: Purify recombinant AOP2 and AOP3 and perform steady-state kinetics with C3-C8 methylsulfinylalkyl glucosinolates, including product and by-product identification by LC-MS, to define specificity and mechanism.
Experiment: Swap residues between AOP2 and AOP3 guided by homology models or crystal structures to identify determinants of alkenylation versus hydroxylation.
Experiment: Complement a Col-0 background (non-functional AOP2) with catalytically dead AOP2 (Fe-binding His mutants) versus wild-type AOP2 to separate enzymatic from possible non-enzymatic effects on glucosinolate accumulation and downstream traits.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)