moaD (PP_1293) encodes the small sulfur-carrier subunit of molybdopterin synthase, a ubiquitin-like beta-grasp protein ending in the conserved Gly-Gly motif. By orthology with Escherichia coli MoaD, its C-terminal glycine is adenylated by MoeB and converted to a thiocarboxylate; two sulfur-loaded MoaD subunits, bound to the MoaE catalytic subunits of the MoaD2-MoaE2 synthase, then donate the dithiolene sulfurs that convert cyclic pyranopterin monophosphate into molybdopterin during molybdenum cofactor biosynthesis.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0006777 Mo-molybdopterin cofactor biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: MoaD is the sulfur carrier required for molybdopterin formation. Reason: Q88NB9 is in the MoaD family (NCBIfam TIGR01682, PANTHER PTHR33359:SF1 with E. coli MoaD). The E. coli ortholog donates the dithiolene sulfurs to precursor Z (PMID:17223713), so the protein does work in the process. Same action as genes/ECOLI/moaD. Supporting Evidence: file:PSEPK/moaD/moaD-deep-research-openscientist.md The gene **moaD** (UniProt **Q88NB9**; ordered locus **PP_1293**) of *Pseudomonas putida* strain KT2440 encodes the **small sulfur-carrier subunit of molybdopterin (MPT) synthase**, the enzyme that catalyzes the **second of the four conserved steps of molybdenum cofactor (Moco) biosynthesis**. PMID:17223713 In Escherichia coli, the MoaD protein plays a central role in the conversion of precursor Z to molybdopterin (MPT) during molybdenum cofactor biosynthesis. |
| GO:1990133 molybdopterin adenylyltransferase complex | IEA GO_REF:0000118 | ACCEPT | Summary: MoaD participates in the transient MoeB-MoaD adenylyltransferase complex during carrier activation. Reason: The GO definition of GO:1990133 names MoeB and MoaD as its E. coli subunits. The complex evidence is ortholog evidence: crystal structures of the Escherichia coli MoeB-MoaD complex in apo, ATP-bound and MoaD-adenylate forms (PMID:11713534). Q88NB9 is placed in the MoaD family by the NCBIfam TIGR01682 moaD model; no KT2440 complex has been isolated. Same action as genes/ECOLI/moaD. Supporting Evidence: PMID:11713534 Here we present the crystal structures of the MoeB-MoaD complex in its apo, ATP-bound, and MoaD-adenylate forms file:PSEPK/moaD/moaD-uniprot.txt DR NCBIfam; TIGR01682; moaD; 1. |
| GO:0097163 sulfur carrier activity | ISS file:interpro/panther/PTHR33359/PTHR33359-entries.csv | NEW | Summary: Q88NB9 is the molybdopterin-synthase sulfur carrier. Reason: Q88NB9 and the reviewed E. coli MoaD P30748 are in the same PANTHER subfamily (PTHR33359:SF1) and the MoaD NCBIfam family. GO:0097163 is defined as "Covalently binding to sulfur and delivering it to an acceptor molecule"; E. coli MoaD carries a transferable C-terminal thiocarboxylate that donates sulfur to precursor Z. Same NEW term as genes/ECOLI/moaD. Supporting Evidence: file:PSEPK/moaD/moaD-uniprot.txt DR PANTHER; PTHR33359:SF1; MOLYBDOPTERIN SYNTHASE SULFUR CARRIER SUBUNIT; 1. file:interpro/panther/PTHR33359/PTHR33359-entries.csv P30748,Molybdopterin synthase sulfur carrier subunit,protein,83333,Escherichia coli (strain K12),Escherichia coli (strain K12),moaD,81,PTHR33359:SF1,MOLYBDOPTERIN SYNTHASE SULFUR CARRIER SUBUNIT,True PMID:17223713 MoaD has a fold similar to that of ubiquitin and contains a highly conserved C-terminal Gly-Gly motif, which in its active form contains a transferrable sulfur in the form of a thiocarboxylate group. |
| GO:1990140 molybdopterin synthase complex | ISS file:interpro/panther/PTHR33359/PTHR33359-entries.csv | NEW | Summary: Q88NB9 is proposed as a component of the MoaD-MoaE molybdopterin synthase complex. Reason: Q88NB9 and Escherichia coli MoaD P30748 occupy the same PTHR33359:SF1 sulfur-carrier subfamily, and Q88NB9 is encoded directly beside its MoaE partner. The E. coli MoaD2-MoaE2 heterotetramer is established structurally, so GO:1990140 is supported by sequence similarity rather than direct KT2440 complex measurement. Supporting Evidence: file:ECOLI/moaD/moaD-uniprot.txt SUBUNIT: Heterotetramer of 2 MoaD subunits and 2 MoaE subunits. file:PSEPK/moaD/moaD-deep-research-openscientist.md Mechanistically, MoaD operates within a **MoaD₂–MoaE₂ heterotetramer**. Each MoaD subunit inserts its reactive C-terminus deep into a MoaE catalytic subunit, positioning the C-terminal Gly-thiocarboxylate adjacent to the substrate **cyclic pyranopterin monophosphate (cPMP / precursor Z)**. file:interpro/panther/PTHR33359/PTHR33359-entries.csv P30748,Molybdopterin synthase sulfur carrier subunit,protein,83333,Escherichia coli (strain K12),Escherichia coli (strain K12),moaD,81,PTHR33359:SF1,MOLYBDOPTERIN SYNTHASE SULFUR CARRIER SUBUNIT,True |
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Download this section (compressed HTML)Q: Which KT2440 sulfur-donor system converts adenylated MoaD to the active thiocarboxylate under physiological conditions?
Experiment: Reconstitute Q88NB9 activation and thiocarboxylation with MoeB and candidate sulfur-donor proteins, then assay molybdopterin formation with MoaE.
Type: biochemical pathway reconstitution
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