Putative NAD(P)H-dependent FMN reductase SsuE (VPARA_09290, A0A0H2M6H0; EC 1.5.1.38) in Variovorax paradoxus strain TBEA6 is a 194-amino-acid cytosolic flavin reductase (NCBIfam TIGR03567, InterPro IPR020048, PANTHER PTHR43408:SF1, Pfam PF03358 residues 1-142) of the two-component alkanesulfonate monooxygenase system. Encoded on genomic contig JZWI01000005 (EMBL KLN57918.1) at the 3' end of the aliphatic sulfonate uptake and desulfonation gene cluster alongside the ABC importer subunits ssuB2 (VPARA_09230, KLN57912.1), ssuC5 (VPARA_09240, KLN57913.1), and ssuA2 (VPARA_09270, KLN57916.1) and the alkanesulfonate monooxygenase ssuD (VPARA_09250, KLN57914.1), SsuE catalyzes the NAD(P)H-dependent reduction of oxidized FMN to reduced FMN (FMNH2) and supplies the reduced flavin cosubstrate required by SsuD for oxygenolytic carbon-sulfur bond cleavage of aliphatic sulfonates to sulfite and the corresponding aldehyde.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0008752 FMN reductase [NAD(P)H] activity | IEA GO_REF:0000002 | ACCEPT | Summary: Core catalytic activity of SsuE (NCBIfam TIGR03567, InterPro IPR020048, PANTHER PTHR43408:SF1), which reduces FMN using NAD(P)H to provide reduced flavin to the partner alkanesulfonate monooxygenase SsuD. Reason: VPARA_09290 belongs to the SsuE family of two-component FMN reductases (NCBIfam TIGR03567, InterPro IPR020048, PANTHER PTHR43408:SF1, Pfam PF03358) and is co-localized in the contig JZWI01000005 ssu cluster with ssuD (VPARA_09250, UniProtKB:A0A0H2MCI3). Because SsuE homologs vary in nicotinamide cofactor preference across bacteriaβPseudomonas putida S-313 SsuE prefers NADPH (PMID:10781557) whereas E. coli SsuE utilizes both NADPH and NADH (PMID:10480865)βand VPARA_09290 has not been biochemically assayed, GO:0008752 (FMN reductase [NAD(P)H] activity) is accepted at the warranted level of cofactor specificity. Supporting Evidence: file:VARPD/ssuE/ssuE-uniprot.txt DR NCBIfam; TIGR03567; FMN_reduc_SsuE; 1. PMID:10480865 SsuE is the FMN reducing enzyme providing SsuD with FMNH(2). PMID:10781557 SsuE revealed NADPH-dependent FMN reductase activity and lower levels of FAD reductase activity (32% of the value with FMN). No activity was observed with NADH. |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: True but uninformative parent molecular function already entailed by the accepted specific child term GO:0008752 (FMN reductase [NAD(P)H] activity). Reason: GO:0016491 (oxidoreductase activity) is a broad ancestor term that adds no specificity beyond GO:0008752 (FMN reductase [NAD(P)H] activity) already accepted in this review. Supporting Evidence: file:VARPD/ssuE/ssuE-uniprot.txt FT DOMAIN 1..142 FT /note="NADPH-dependent FMN reductase-like" FT /evidence="ECO:0000259|Pfam:PF03358" |
| GO:0046306 alkanesulfonate catabolic process | IEA GO_REF:0000002 | ACCEPT | Summary: Core pathway process in which SsuE supplies reduced FMN (FMNH2) to the co-encoded alkanesulfonate monooxygenase SsuD (VPARA_09250) for oxidative desulfonation of aliphatic sulfonates. Reason: SsuE (VPARA_09290, KLN57918.1) belongs to the SsuE family (NCBIfam TIGR03567, InterPro IPR020048) and is co-encoded in the contig JZWI01000005 ssuB2-ssuC5-ssuD-...-ssuA2-...-ssuE gene cluster alongside ssuB2 (VPARA_09230, UniProtKB:A0A0H2MBB8), ssuC5 (VPARA_09240, UniProtKB:A0A0H2M6G6), ssuD (VPARA_09250, UniProtKB:A0A0H2MCI3), and ssuA2 (VPARA_09270, UniProtKB:A0A0H2M784), where it serves as the reduced-flavin supplier for SsuD during alkanesulfonate catabolism (PMID:10480865, PMID:26634408). Supporting Evidence: file:VARPD/ssuE/ssuE-uniprot.txt DR NCBIfam; TIGR03567; FMN_reduc_SsuE; 1. PMID:10480865 SsuD catalysis was absolutely dependent on FMNH(2) and oxygen |
| GO:0052873 FMN reductase (NADPH) activity | IEA GO_REF:0000003 | MARK AS OVER ANNOTATED | Summary: Over-specific nicotinamide cofactor assignment from EC:1.5.1.38 mapping; NADPH vs NADH preference has not been experimentally assayed in Variovorax paradoxus SsuE, and GO:0008752 (FMN reductase [NAD(P)H] activity) is accepted instead. Reason: EC:1.5.1.38 maps automatically to GO:0052873 (FMN reductase (NADPH) activity). While Pseudomonas putida S-313 SsuE uses NADPH specifically in extract assays (PMID:10781557), E. coli SsuE utilizes both NADPH and NADH (PMID:10480865), and the nicotinamide cofactor preference of Variovorax paradoxus TBEA6 SsuE (VPARA_09290) has not been biochemically determined; the parent term GO:0008752 (FMN reductase [NAD(P)H] activity) is accepted as the core molecular function. Supporting Evidence: file:VARPD/ssuE/ssuE-uniprot.txt DR NCBIfam; TIGR03567; FMN_reduc_SsuE; 1. PMID:10480865 SsuE is the FMN reducing enzyme providing SsuD with FMNH(2). PMID:10781557 SsuE revealed NADPH-dependent FMN reductase activity and lower levels of FAD reductase activity (32% of the value with FMN). No activity was observed with NADH. |
| GO:0005829 cytosol | IC PMID:10480865 Characterization of a two-component alkanesulfonate monooxyg... | NEW | Summary: Core subcellular localization of this soluble 194-aa intracellular flavin reductase that supplies reduced FMN to cytosolic SsuD. Reason: Inferred by curator (IC) because SsuE (VPARA_09290) is a 194-residue soluble cytoplasmic flavin reductase (Pfam PF03358, residues 1-142) lacking signal peptides or transmembrane helices that transfers reduced FMN to the cytosolic monooxygenase SsuD (VPARA_09250, UniProtKB:A0A0H2MCI3) in the cytosol (GO:0005829; PMID:10480865). Supporting Evidence: file:VARPD/ssuE/ssuE-uniprot.txt FT DOMAIN 1..142 FT /note="NADPH-dependent FMN reductase-like" FT /evidence="ECO:0000259|Pfam:PF03358" PMID:10480865 SsuE is the FMN reducing enzyme providing SsuD with FMNH(2). |
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Download this section (compressed HTML)Q: Does Variovorax paradoxus TBEA6 SsuE (VPARA_09290) exhibit strict NADPH preference like Pseudomonas putida S-313 SsuE or dual NADH/NADPH activity like Escherichia coli SsuE, and can alternative flavin reductases in TBEA6 support SsuD (VPARA_09250) activity in a ΞssuE background?
Suggested experts: Ellis HR, Kertesz MA
Experiment: Purify recombinant Variovorax paradoxus SsuE (A0A0H2M6H0) and measure steady-state kinetic parameters (kcat, Km) with NADPH versus NADH and FMN versus FAD, as well as coupled desulfonation of octanesulfonate with purified V. paradoxus SsuD (A0A0H2MCI3).
Hypothesis: V. paradoxus SsuE efficiently reduces FMN and couples with SsuD (VPARA_09250) to drive stoichiometric sulfite release from linear alkanesulfonates.
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