SOT18 (AtSOT18, AtST5b, At1g74090) is a cytosolic PAPS-dependent sulfotransferase that catalyzes the final step of core glucosinolate structure formation, sulfating desulfoglucosinolates with 3'-phosphoadenosine 5'-phosphosulfate to produce glucosinolates and adenosine 3',5'-bisphosphate. Like its paralogs SOT16 (ST5a) and SOT17 (ST5c) it accepts a broad range of desulfoglucosinolates in vitro, with the C24 enzyme preferring long-chain methionine-derived substrates such as 7-methylthioheptyl and 8-methylthiooctyl desulfoglucosinolates. Natural allelic variation between accessions (two amino-acid differences between the C24 and Col-0 proteins) alters its substrate specificity, making SOT18 a candidate contributor to accession differences in aliphatic glucosinolate profiles. It is inhibited by the reaction product PAP.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | EXP PMID:16367753 The three desulfoglucosinolate sulfotransferase proteins in ... | ACCEPT | Summary: GFP fusion constructs of AtSOT16, AtSOT17 and AtSOT18 transiently expressed in Arabidopsis protoplasts localized to the cytoplasm. Reason: Direct experimental localization; the cytoplasm (cytosol) is where desulfoglucosinolate sulfation takes place. Supporting Evidence: PMID:16367753 All three desulfoglucosinolate AtSOT proteins are localized in the cytoplasm, as demonstrated by transient expression of fusion constructs with the green fluorescent protein in Arabidopsis protoplasts. |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of cytoplasmic activity for the cytosolic sulfotransferase family; consistent with GFP localization of AtSOT16-18. Reason: Experimentally supported by GFP fusion localization of all three desulfoglucosinolate SOTs in protoplasts. Supporting Evidence: PMID:16367753 All three desulfoglucosinolate AtSOT proteins are localized in the cytoplasm, as demonstrated by transient expression of fusion constructs with the green fluorescent protein in Arabidopsis protoplasts. |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping to cytoplasm, based on the experimental GFP data. Reason: Consistent with direct experimental localization. Supporting Evidence: PMID:16367753 All three desulfoglucosinolate AtSOT proteins are localized in the cytoplasm, as demonstrated by transient expression of fusion constructs with the green fluorescent protein in Arabidopsis protoplasts. |
| GO:0005737 cytoplasm | ISM GO_REF:0000122 | ACCEPT | Summary: AtSubP predicted cytoplasmic localization. Reason: Consistent with direct experimental localization. Supporting Evidence: PMID:16367753 All three desulfoglucosinolate AtSOT proteins are localized in the cytoplasm, as demonstrated by transient expression of fusion constructs with the green fluorescent protein in Arabidopsis protoplasts. |
| GO:0008146 sulfotransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: The enzyme sulfates both aromatic and aliphatic desulfoglucosinolates. Reason: Replace broad sulfotransferase activity with both supported substrate-class activities already present, rather than selecting one and discarding demonstrated breadth. Substrate preferences vary between enzymes and, for SOT18, between C24 and Col-0 alleles. |
| GO:0019761 glucosinolate biosynthetic process | IDA PMID:15358770 Desulfoglucosinolate sulfotransferases from Arabidopsis thal... | ACCEPT | Summary: Recombinant SOT18 (AtST5b) catalyzes sulfation of desulfoglucosinolates, the final step of core glucosinolate structure formation. Reason: The enzyme catalyzes a biosynthetic step of the glucosinolate core pathway (direct participation), so this process is a core annotation. Supporting Evidence: PMID:15358770 The three enzymes were shown to catalyze the final step in the biosynthesis of the glucosinolate (GS) core structure, the sulfation of desulfoglucosinolates (dsGSs). They accept a broad range of dsGSs as substrates. |
| GO:0019761 glucosinolate biosynthetic process | IDA PMID:19077143 Kinetics and substrate specificities of desulfo-glucosinolat... | ACCEPT | Summary: Purified recombinant AtSOT18 sulfates desulfoglucosinolates, the last step of glucosinolate core structure biosynthesis, with a preference for long-chain methionine-derived substrates. Reason: Direct catalytic participation in glucosinolate biosynthesis. Supporting Evidence: PMID:19077143 three SOTs were identified to catalyze the last step of glucosinolate (Gl) core structure biosynthesis called AtSOT16, 17 and 18 PMID:19077143 AtSOT18 preferred the long-chain ds-Gl, 7-methylthioheptyl and 8-methylthiooctyl, derived from methionine |
| GO:0047364 aromatic desulfoglucosinolate sulfotransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT propagation of desulfoglucosinolate sulfotransferase activity within the Arabidopsis SOT16/17/18 clade (PTN004305968); the target is among the experimentally characterized donors, which is expected. Reason: SOT18 has direct in vitro activity with aromatic desulfobenzylglucosinolate as well as aliphatic substrates; all three clade members accept a broad range of desulfoglucosinolates. Supporting Evidence: PMID:15358770 The three enzymes were shown to catalyze the final step in the biosynthesis of the glucosinolate (GS) core structure, the sulfation of desulfoglucosinolates (dsGSs). They accept a broad range of dsGSs as substrates. |
| GO:0047364 aromatic desulfoglucosinolate sulfotransferase activity | IDA PMID:15358770 Desulfoglucosinolate sulfotransferases from Arabidopsis thal... | ACCEPT | Summary: Purified His-tagged SOT18 sulfated a broad range of desulfoglucosinolates, including aromatic (phenylalanine-derived) substrates, although it prefers long-chain methionine-derived substrates in competition. Reason: GO:0047364 is defined by conversion of desulfoglucotropaeolin (desulfobenzylglucosinolate) and indolylmethyl desulfoglucosinolate; the enzyme is active with these substrates, although aliphatic desulfoglucosinolates are its preferred physiological substrates. Supporting Evidence: PMID:15358770 The three enzymes were shown to catalyze the final step in the biosynthesis of the glucosinolate (GS) core structure, the sulfation of desulfoglucosinolates (dsGSs). They accept a broad range of dsGSs as substrates. PMID:15358770 long chain dsGSs derived from methionine are the preferred substrates of AtST5b and AtST5c |
| GO:0047364 aromatic desulfoglucosinolate sulfotransferase activity | IDA PMID:19077143 Kinetics and substrate specificities of desulfo-glucosinolat... | ACCEPT | Summary: Kinetic characterization of recombinant AtSOT18 (C24 and Col-0 alleles) with multiple desulfoglucosinolates, including aromatic substrates (activity on indolic substrates is not stated in the cached abstract). Reason: Activity on aromatic desulfoglucosinolates is demonstrated in vitro, although the enzyme prefers long-chain aliphatic substrates. Supporting Evidence: PMID:19077143 Recombinant proteins were used to determine substrate specificities to investigate whether each of the three desulfo (ds)-Gl SOTs might influence the Gl pattern of Arabidopsis differently. |
| GO:0051923 sulfation | IBA GO_REF:0000033 | ACCEPT | Summary: Sulfation (addition of a sulfate group to a molecule) propagated across the cytosolic sulfotransferase family. Reason: SOT18 transfers the sulfate group from PAPS to desulfoglucosinolates, so it directly performs sulfation; the process is general, with glucosinolate biosynthesis being the specific biological context. Supporting Evidence: PMID:16367753 Sulfotransferases (SOTs) catalyse the transfer of a sulfate group from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to an appropriate hydroxy group of various substrates PMID:16367753 Three of them, AtSOT16, AtSOT17 and AtSOT18, catalyse the sulfation of desulfoglucosinolates. |
| GO:0120527 aliphatic desulfoglucosinolate sulfotransferase activity | EXP PMID:16367753 The three desulfoglucosinolate sulfotransferase proteins in ... | ACCEPT | Summary: Enzyme kinetics with purified recombinant AtSOT18 on desulfo-3-methylthiopropyl, -4-methylthiobutyl and other aliphatic desulfoglucosinolates. Reason: Core molecular function with direct experimental support. Supporting Evidence: PMID:16367753 Three of them, AtSOT16, AtSOT17 and AtSOT18, catalyse the sulfation of desulfoglucosinolates. PMID:16367753 They show different maximum velocities with several desulfoglucosinolates as substrates and differ in their affinity for desulfobenzylglucosinolate and PAPS. |
| GO:0120527 aliphatic desulfoglucosinolate sulfotransferase activity | IDA PMID:19077143 Kinetics and substrate specificities of desulfo-glucosinolat... | ACCEPT | Summary: AtSOT18 prefers the long-chain methionine-derived desulfoglucosinolates 7-methylthioheptyl and 8-methylthiooctyl in vitro. Reason: Core molecular function; aliphatic desulfoglucosinolates are the preferred substrates. Supporting Evidence: PMID:19077143 AtSOT18 preferred the long-chain ds-Gl, 7-methylthioheptyl and 8-methylthiooctyl, derived from methionine |
| GO:0120527 aliphatic desulfoglucosinolate sulfotransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Rhea/EC-based electronic annotation (RHEA:52724, EC 2.8.2.38) to aliphatic desulfoglucosinolate sulfotransferase activity. Reason: Core molecular function; experimentally supported by in vitro kinetics showing preference for long-chain methionine-derived aliphatic desulfoglucosinolates. Supporting Evidence: PMID:15358770 long chain dsGSs derived from methionine are the preferred substrates of AtST5b and AtST5c PMID:19077143 AtSOT18 preferred the long-chain ds-Gl, 7-methylthioheptyl and 8-methylthiooctyl, derived from methionine |
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Download this section (compressed HTML)Q: Does the C24 versus Col-0 SOT18 allelic difference contribute to natural variation in long-chain aliphatic glucosinolate accumulation between accessions?
Q: How redundant are SOT18 and SOT17 for long-chain aliphatic desulfoglucosinolate sulfation in planta?
Experiment: Swap the C24 and Col-0 SOT18 alleles in a sot18 background and measure 7-methylthioheptyl and 8-methylthiooctyl glucosinolate levels to test the in vivo impact of the specificity-altering residues.
Experiment: Profile desulfoglucosinolates in sot17 sot18 double mutants to determine whether these SOTs are rate-limiting for long-chain aliphatic glucosinolate formation.
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