XdhB is the molybdopterin-cofactor catalytic subunit of the two-subunit XdhAB xanthine dehydrogenase. It houses the purine-base oxidation center and works with the FAD/[2Fe-2S] electron-transfer subunit XdhA to convert hypoxanthine to xanthine and xanthine to urate. These reactions have not been measured directly for the KT2440 complex and are inferred from subunit-specific domain architecture and homologous bacterial XDH biochemistry.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004854 xanthine dehydrogenase activity | IEA GO_REF:0000003 | MODIFY | Summary: XdhB contains the molybdenum catalytic center but requires XdhA to form the complete xanthine dehydrogenase. Reason: Replace the EC-derived enables relation with contributes_to because XdhB supplies only the molybdopterin catalytic module of the assembled XdhAB electron-transfer system. Proposed replacements: xanthine dehydrogenase activity Supporting Evidence: file:PSEPK/xdhB/xdhB-uniprot.txt DR InterPro; IPR014309; Xanthine_DH_Mopterin-bd_su. PMID:11341925 XDH from P. putida 86 consists of 91.0 kDa and 46.2 kDa file:PSEPK/xdhB/xdhB-deep-research-openscientist.md encodes the **large molybdenum-cofactor (molybdopterin)-binding catalytic subunit of a two-subunit bacterial xanthine dehydrogenase** |
| GO:0005506 iron ion binding | IEA GO_REF:0000002 | REMOVE | Summary: The XdhB sequence is assigned to the molybdopterin-binding catalytic subunit rather than the Fe-S-bearing subunit. Reason: XdhB contains the xanthine-dehydrogenase molybdopterin-binding architecture; the complementary XdhA subunit carries the ferredoxin-type [2Fe-2S] domains. The broad InterPro iron mapping appears to have crossed the multi-subunit enzyme boundary. Supporting Evidence: file:PSEPK/xdhB/xdhB-uniprot.txt DR InterPro; IPR014309; Xanthine_DH_Mopterin-bd_su. file:PSEPK/xdhA/xdhA-uniprot.txt DR InterPro; IPR006058; 2Fe2S_fd_BS. file:PSEPK/xdhB/xdhB-deep-research-openscientist.md with no FAD- or iron-sulfur-binding regions |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000120 | ACCEPT | Summary: XdhB houses the molybdenum center at which substrate oxidation occurs. Reason: This broad intrinsic redox function is appropriate for the catalytic subunit, while the substrate-specific complete activities are represented separately with contributes_to relations. Supporting Evidence: file:PSEPK/xdhB/xdhB-uniprot.txt DR InterPro; IPR014309; Xanthine_DH_Mopterin-bd_su. |
| GO:0030151 molybdenum ion binding | IEA GO_REF:0000002 | MODIFY | Summary: XdhB binds molybdenum as part of an organic molybdopterin cofactor rather than as a free ion. Reason: GO:0043546 describes the biologically relevant cofactor-binding state more accurately. Proposed replacements: molybdopterin cofactor binding Supporting Evidence: file:PSEPK/xdhB/xdhB-uniprot.txt DR InterPro; IPR008274; AldOxase/xan_DH_MoCoBD1. |
| GO:0043546 molybdopterin cofactor binding | ISS | NEW | Summary: XdhB is the molybdopterin-binding subunit of bacterial XDH. Reason: The subunit-specific InterPro architecture supports the cofactor-level replacement for free molybdenum binding. Supporting Evidence: file:PSEPK/xdhB/xdhB-uniprot.txt DR InterPro; IPR014309; Xanthine_DH_Mopterin-bd_su. |
| GO:0070674 hypoxanthine dehydrogenase activity | ISS | NEW | Summary: XdhB contributes the molybdenum catalytic subunit to XdhAB oxidation of hypoxanthine to xanthine. Reason: The characterized P. putida strain-86 homolog oxidizes hypoxanthine, while the exact KT2440 sequence identifies the corresponding XdhB subunit architecture. Supporting Evidence: PMID:11341925 oxidation of hypoxanthine, xanthine, purine, and some aromatic aldehydes, using file:PSEPK/xdhB/xdhB-uniprot.txt SubName: Full=Xanthine dehydrogenase subunit XdhB |
| GO:0009114 hypoxanthine catabolic process | ISS | NEW | Summary: XdhB contributes the catalytic center for the XdhAB hypoxanthine-to-xanthine step. Reason: This is the immediate process for the first purine-base reaction of the homologous two-subunit enzyme. Supporting Evidence: PMID:11341925 oxidation of hypoxanthine, xanthine, purine, and some aromatic aldehydes, using |
| GO:0009115 xanthine catabolic process | ISS | NEW | Summary: XdhB contributes the catalytic center for XdhAB oxidation of xanthine to urate. Reason: Xanthine oxidation is the defining reaction of the homologous P. putida strain-86 XDH. Supporting Evidence: PMID:11341925 oxidation of hypoxanthine, xanthine, purine, and some aromatic aldehydes, using |
| GO:0034418 urate biosynthetic process | ISS | NEW | Summary: The XdhAB xanthine oxidation step directly produces urate. Reason: This process annotation follows from the inferred xanthine dehydrogenase reaction of the assembled KT2440 complex. Supporting Evidence: PMID:11341925 oxidation of hypoxanthine, xanthine, purine, and some aromatic aldehydes, using |
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Download this section (compressed HTML)Q: Does Q88F20 bind mature molybdopterin cofactor and support both XdhAB purine-base reactions in KT2440?
Suggested experts: bacterial molybdenum-enzyme experts
Experiment: Reconstitute mature KT2440 XdhAB, verify molybdenum-cofactor incorporation into XdhB, and assay hypoxanthine- and xanthine-dependent NAD+ reduction.
Type: enzyme reconstitution assay
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