THI20 (YOL055C) encodes the major hydroxymethylpyrimidine (HMP)/HMP-phosphate kinase of Saccharomyces cerevisiae, a ThiD-TenA fusion protein of the THI20/THI21/THI22 family. Its N-terminal ThiD-like ribokinase domain phosphorylates HMP-P to HMP-PP (EC 2.7.4.7), the activated pyrimidine that Thi6 couples to the thiazole to make thiamine monophosphate, and also phosphorylates HMP to HMP-P (EC 2.7.1.49), allowing salvage of free HMP. Its C-terminal TenA-like domain has thiaminase II activity in vitro, hydrolysing thiamine to HMP and 4-methyl-5-(2-hydroxyethyl)thiazole, making Thi20 trifunctional with both biosynthetic and degradative activity; the physiological role of the thiaminase activity (thiamine recycling/salvage) is not established. Thi20 is cytosolic, induced by thiamine starvation as part of the THI regulon, and is functionally redundant with THI21 for HMP-P kinase activity.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005829 cytosol | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from the ThiD HMP-P kinase family node (PTN000466159) with E. coli ThiD and yeast Thi20 as donors. Cytosolic location is also shown directly for Thi20 (IDA below). Supporting Evidence: PMID:16850348 Our analysis helps to further define the THI regulon and hence the spectrum of genes/proteins involved in the ThDP homeostasis. |
| GO:0005829 cytosol | IDA PMID:16850348 Pdc2 coordinates expression of the THI regulon in the yeast ... | ACCEPT | Summary: Mojzita & Hohmann 2006 analysed THI-regulon proteins including localisation; the SGD curator recorded cytosolic Thi20 from this work (abstract-only cache; deferring to curator). Consistent with absence of targeting signals. Supporting Evidence: PMID:16850348 Our analysis helps to further define the THI regulon and hence the spectrum of genes/proteins involved in the ThDP homeostasis. |
| GO:0005829 cytosol | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways PWY3O-17 cytosolic step assignment; consistent with the IDA. Supporting Evidence: file:yeast/THI20/THI20-uniprot.txt amino-2-methyl-5-diphosphomethylpyrimidine from 5-amino-1-(5-phospho-D- |
| GO:0006772 thiamine metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro IPR027574 (thiaminase II) mapping to the general thiamine metabolic process. Correct but uninformative; Thi20 is better described by its specific biosynthetic (HMP-P kinase) and degradative (thiaminase) processes, both annotated separately. Proposed replacements: thiamine biosynthetic process Supporting Evidence: PMID:15967475 This demonstrates that Thi20 is a trifunctional protein with thiamin biosynthetic and degradative activity. |
| GO:0008902 hydroxymethylpyrimidine kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA for HMP kinase from the ThiD node (E. coli ThiD donor; Thi20 and Thi21 appear in with/from because of their own experimental annotations). Thi20 is within the clade and the activity is directly demonstrated. Supporting Evidence: PMID:15967475 Incubation of Thi20 with thiamin reveals that it has thiaminase II activity, in addition, incubation of Thi20 with HMP (4-amino-2-methyl-5-hydroxymethylpyrimidine) and ATP reveals that it has HMP kinase and HMP-P (4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate) kinase activity. |
| GO:0008902 hydroxymethylpyrimidine kinase activity | IDA PMID:15614489 Biosynthesis of hydroxymethylpyrimidine pyrophosphate in Sac... | ACCEPT | Summary: Kawasaki et al. 2005 showed with partially purified protein that Thi20 converts HMP to HMP-PP (HMP kinase plus HMP-P kinase), Thi20 being much more efficient than Thi21. Supporting Evidence: PMID:15614489 we demonstrate that both Thi20p and Thi21p proteins also have HMP kinase activity. PMID:15614489 Although each isoform independently can synthesize HMP pyrophosphate (HMP-PP) from HMP, there is a marked difference in efficiency between the two proteins. |
| GO:0008902 hydroxymethylpyrimidine kinase activity | IDA PMID:15967475 Thi20, a remarkable enzyme from Saccharomyces cerevisiae wit... | ACCEPT | Summary: Haas et al. 2005 incubated recombinant Thi20 with HMP and ATP and detected HMP kinase activity. Supporting Evidence: PMID:15967475 Incubation of Thi20 with thiamin reveals that it has thiaminase II activity, in addition, incubation of Thi20 with HMP (4-amino-2-methyl-5-hydroxymethylpyrimidine) and ATP reveals that it has HMP kinase and HMP-P (4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate) kinase activity. |
| GO:0008902 hydroxymethylpyrimidine kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (RHEA:23096, EC 2.7.1.49). Correct for Thi20 and matches the experimental data. Supporting Evidence: PMID:15967475 Incubation of Thi20 with thiamin reveals that it has thiaminase II activity, in addition, incubation of Thi20 with HMP (4-amino-2-methyl-5-hydroxymethylpyrimidine) and ATP reveals that it has HMP kinase and HMP-P (4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate) kinase activity. |
| GO:0008902 hydroxymethylpyrimidine kinase activity | IGI PMID:15614489 Biosynthesis of hydroxymethylpyrimidine pyrophosphate in Sac... | ACCEPT | Summary: IGI with E. coli thiC (P30136): Kawasaki et al. used complementation of E. coli thiamine mutants; THI20 restored HMP-dependent thiamine synthesis. Abstract-only record; deferring to curator, consistent with biochemistry. Supporting Evidence: PMID:15614489 we demonstrate that both Thi20p and Thi21p proteins also have HMP kinase activity. |
| GO:0008902 hydroxymethylpyrimidine kinase activity | IGI PMID:15614489 Biosynthesis of hydroxymethylpyrimidine pyrophosphate in Sac... | ACCEPT | Summary: IGI with E. coli pdxK (P40191, a B6 kinase that can also phosphorylate HMP); same complementation system. Accepted, deferring to the curator who read the full text. Supporting Evidence: PMID:15614489 we demonstrate that both Thi20p and Thi21p proteins also have HMP kinase activity. |
| GO:0008902 hydroxymethylpyrimidine kinase activity | IGI PMID:15614489 Biosynthesis of hydroxymethylpyrimidine pyrophosphate in Sac... | ACCEPT | Summary: IGI with E. coli thiD (P76422): Thi20 complements the HMP/HMP-P kinase deficiency. Supporting Evidence: PMID:15614489 we demonstrate that both Thi20p and Thi21p proteins also have HMP kinase activity. |
| GO:0008902 hydroxymethylpyrimidine kinase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA assigning Thi20 to the ATP + HMP -> HMP-P step (EC 2.7.1.49). Correct for Thi20, though Kawasaki et al. note HMP may not be an intermediate of de novo synthesis in yeast (THI5-family enzymes make HMP-P directly), so this step mainly serves HMP salvage. Supporting Evidence: PMID:15967475 Incubation of Thi20 with thiamin reveals that it has thiaminase II activity, in addition, incubation of Thi20 with HMP (4-amino-2-methyl-5-hydroxymethylpyrimidine) and ATP reveals that it has HMP kinase and HMP-P (4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate) kinase activity. PMID:15614489 We discuss the possibility that HMP is not involved in the pathway of de novo thiamin synthesis in S. cerevisiae. |
| GO:0008972 phosphomethylpyrimidine kinase activity | EXP PMID:15967475 Thi20, a remarkable enzyme from Saccharomyces cerevisiae wit... | ACCEPT | Summary: Haas et al. 2005 directly assayed recombinant Thi20 HMP-P kinase activity. Core activity. Supporting Evidence: PMID:15967475 Incubation of Thi20 with thiamin reveals that it has thiaminase II activity, in addition, incubation of Thi20 with HMP (4-amino-2-methyl-5-hydroxymethylpyrimidine) and ATP reveals that it has HMP kinase and HMP-P (4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate) kinase activity. |
| GO:0008972 phosphomethylpyrimidine kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from ThiD HMP-P kinase node; Thi20 within clade and experimentally validated. Supporting Evidence: PMID:15967475 Incubation of Thi20 with thiamin reveals that it has thiaminase II activity, in addition, incubation of Thi20 with HMP (4-amino-2-methyl-5-hydroxymethylpyrimidine) and ATP reveals that it has HMP kinase and HMP-P (4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate) kinase activity. |
| GO:0008972 phosphomethylpyrimidine kinase activity | IDA PMID:15614489 Biosynthesis of hydroxymethylpyrimidine pyrophosphate in Sac... | ACCEPT | Summary: Kawasaki et al. 2005 reconstitution: Thi20 synthesises HMP-PP from HMP-P. Supporting Evidence: PMID:15614489 Two redundant genes, THI20 and THI21, of Saccharomyces cerevisiae encode a 2-methyl-4-amino-5-hydroxymethylpyrimidine monophosphate (HMP-P) kinase required for thiamin biosynthesis. PMID:15614489 Although each isoform independently can synthesize HMP pyrophosphate (HMP-PP) from HMP, there is a marked difference in efficiency between the two proteins. |
| GO:0008972 phosphomethylpyrimidine kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (InterPro IPR004399, RHEA:19893, EC 2.7.4.7). Correct; the central activity of Thi20. Supporting Evidence: PMID:15967475 Incubation of Thi20 with thiamin reveals that it has thiaminase II activity, in addition, incubation of Thi20 with HMP (4-amino-2-methyl-5-hydroxymethylpyrimidine) and ATP reveals that it has HMP kinase and HMP-P (4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate) kinase activity. |
| GO:0008972 phosphomethylpyrimidine kinase activity | IGI PMID:10383756 Genetic redundancy and gene fusion in the genome of the Bake... | ACCEPT | Summary: IGI with E. coli thiD (P76422): Llorente et al. 1999 showed THI20/THI21 complement HMP-P kinase deficiency and that two family members are isofunctional HMP-P kinases. Supporting Evidence: PMID:10383756 We demonstrate that two members are isofunctional and encode a hydroxymethylpyrimidine phosphate (HMP-P) kinase (EC 2.7.4.7), an activity required for the final steps of thiamine biosynthesis, whose genes were not previously known in yeast. |
| GO:0008972 phosphomethylpyrimidine kinase activity | IGI PMID:15614489 Biosynthesis of hydroxymethylpyrimidine pyrophosphate in Sac... | ACCEPT | Summary: IGI with E. coli thiC (P30136) from the Kawasaki complementation system. Accepted; deferring to curator. Supporting Evidence: PMID:15614489 Two redundant genes, THI20 and THI21, of Saccharomyces cerevisiae encode a 2-methyl-4-amino-5-hydroxymethylpyrimidine monophosphate (HMP-P) kinase required for thiamin biosynthesis. |
| GO:0008972 phosphomethylpyrimidine kinase activity | IGI PMID:15614489 Biosynthesis of hydroxymethylpyrimidine pyrophosphate in Sac... | ACCEPT | Summary: IGI with E. coli pdxK (P40191) from the Kawasaki complementation system. Accepted; deferring to curator. Supporting Evidence: PMID:15614489 Two redundant genes, THI20 and THI21, of Saccharomyces cerevisiae encode a 2-methyl-4-amino-5-hydroxymethylpyrimidine monophosphate (HMP-P) kinase required for thiamin biosynthesis. |
| GO:0008972 phosphomethylpyrimidine kinase activity | IGI PMID:15614489 Biosynthesis of hydroxymethylpyrimidine pyrophosphate in Sac... | ACCEPT | Summary: IGI with E. coli thiD (P76422) from Kawasaki et al.; consistent with HMP-P kinase function. Supporting Evidence: PMID:15614489 Two redundant genes, THI20 and THI21, of Saccharomyces cerevisiae encode a 2-methyl-4-amino-5-hydroxymethylpyrimidine monophosphate (HMP-P) kinase required for thiamin biosynthesis. |
| GO:0008972 phosphomethylpyrimidine kinase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA for HMP-P + ATP -> HMP-PP (EC 2.7.4.7). Correct and core. Supporting Evidence: file:yeast/THI20/THI20-uniprot.txt amino-2-methyl-5-diphosphomethylpyrimidine from 5-amino-1-(5-phospho-D- |
| GO:0009228 thiamine biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from ThiD family node (E. coli ThiD, Arabidopsis TH1, Aspergillus, yeast Thi20/21/22 donors). Correct inherited role. Supporting Evidence: PMID:10383756 We demonstrate that two members are isofunctional and encode a hydroxymethylpyrimidine phosphate (HMP-P) kinase (EC 2.7.4.7), an activity required for the final steps of thiamine biosynthesis, whose genes were not previously known in yeast. |
| GO:0009228 thiamine biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (ARBA, InterPro IPR004399). Correct. Supporting Evidence: PMID:10383756 We demonstrate that two members are isofunctional and encode a hydroxymethylpyrimidine phosphate (HMP-P) kinase (EC 2.7.4.7), an activity required for the final steps of thiamine biosynthesis, whose genes were not previously known in yeast. |
| GO:0009228 thiamine biosynthetic process | IMP PMID:10383756 Genetic redundancy and gene fusion in the genome of the Bake... | ACCEPT | Summary: Llorente et al. 1999 deletion analysis showed THI20/THI21 required (redundantly) for thiamine biosynthesis via HMP-P kinase. Abstract-only cache; accepted per curator. Supporting Evidence: PMID:10383756 We demonstrate that two members are isofunctional and encode a hydroxymethylpyrimidine phosphate (HMP-P) kinase (EC 2.7.4.7), an activity required for the final steps of thiamine biosynthesis, whose genes were not previously known in yeast. |
| GO:0009228 thiamine biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways PWY3O-17 membership; correct. Supporting Evidence: file:yeast/THI20/THI20-uniprot.txt amino-2-methyl-5-diphosphomethylpyrimidine from 5-amino-1-(5-phospho-D- |
| GO:0009229 thiamine diphosphate biosynthetic process | IEA GO_REF:0000041 | ACCEPT | Summary: UniPathway UPA00060 mapping; HMP-PP formation is part of de novo TPP synthesis. Acceptable. Supporting Evidence: file:yeast/THI20/THI20-uniprot.txt amino-2-methyl-5-diphosphomethylpyrimidine from 5-amino-1-(5-phospho-D- |
| GO:0009230 thiamine catabolic process | IDA PMID:15967475 Thi20, a remarkable enzyme from Saccharomyces cerevisiae wit... | KEEP AS NON CORE | Summary: Based on the in vitro thiaminase II activity of Thi20 (Haas et al. 2005). The activity is real, but whether Thi20 degrades thiamine in vivo, as opposed to salvaging degraded precursors, is not established; non-core. Supporting Evidence: PMID:15967475 Incubation of Thi20 with thiamin reveals that it has thiaminase II activity, in addition, incubation of Thi20 with HMP (4-amino-2-methyl-5-hydroxymethylpyrimidine) and ATP reveals that it has HMP kinase and HMP-P (4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate) kinase activity. PMID:15967475 This demonstrates that Thi20 is a trifunctional protein with thiamin biosynthetic and degradative activity. |
| GO:0050334 thiaminase activity | IDA PMID:15967475 Thi20, a remarkable enzyme from Saccharomyces cerevisiae wit... | KEEP AS NON CORE | Summary: Haas et al. 2005 showed thiaminase II activity of recombinant Thi20 (C-terminal TenA domain). Directly demonstrated, but a secondary activity whose physiological role is unknown. Supporting Evidence: PMID:15967475 Incubation of Thi20 with thiamin reveals that it has thiaminase II activity, in addition, incubation of Thi20 with HMP (4-amino-2-methyl-5-hydroxymethylpyrimidine) and ATP reveals that it has HMP kinase and HMP-P (4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate) kinase activity. |
| GO:0050334 thiaminase activity | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: Combined IEA (InterPro IPR027574, RHEA:17509, EC 3.5.99.2) for thiaminase. Correct for Thi20 (experimentally confirmed); secondary activity. Supporting Evidence: PMID:15967475 Incubation of Thi20 with thiamin reveals that it has thiaminase II activity, in addition, incubation of Thi20 with HMP (4-amino-2-methyl-5-hydroxymethylpyrimidine) and ATP reveals that it has HMP kinase and HMP-P (4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate) kinase activity. |
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Download this section (compressed HTML)Q: Does the TenA-like thiaminase II domain of Thi20 act in vivo to degrade thiamine or to salvage base-degraded thiamine products (as bacterial TenA does), and is it relevant under thiamine-replete or stress conditions?
Experiment: Introduce a catalytic-site mutation into the Thi20 TenA domain (leaving the ThiD domain intact) and measure intracellular thiamine/HMP pools and growth on thiamine degradation products.
Trifunctional enzyme of thiamine biosynthesis, degradation and salvage; has hydroxymethylpyrimidine (HMP) kinase, HMP-phosphate (HMP-P) kinase and thiaminase activities; member of a gene family with THI21 and THI22; HMP and HMP-P kinase activity redundant with Thi21p
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