Periplasmic aliphatic sulfonate-binding protein SsuA2 (VPARA_09270, A0A0H2M784) in Variovorax paradoxus strain TBEA6 is a 319-amino-acid substrate-recognition subunit (NCBIfam TIGR01728, InterPro IPR010067, PANTHER PTHR30024:SF42) of the SsuABC ATP-binding cassette (ABC) importer complex. Encoded on genomic contig JZWI01000005 (EMBL KLN57916.1) within the aliphatic sulfonate uptake and desulfonation gene cluster alongside the ATPase ssuB2 (VPARA_09230, KLN57912.1), the transmembrane permease ssuC5 (VPARA_09240, KLN57913.1), the alkanesulfonate monooxygenase ssuD (VPARA_09250, KLN57914.1), and the FMN reductase ssuE (VPARA_09290, KLN57918.1), SsuA2 carries an N-terminal twin-arginine translocation (Tat) signal peptide (PROSITE PS51318, residues 1-29, containing the Arg8-Arg9-Arg10 motif) that directs export of the mature periplasmic solute-binding domain (residues 30-319) to capture extracellular aliphatic sulfonates and present them to the inner-membrane SsuC5-SsuB2 translocon.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016020 membrane | IEA GO_REF:0000002 | REMOVE | Summary: Incorrect InterPro2GO propagation from IPR010067; mature SsuA2 (residues 30-319) is a soluble periplasmic solute-binding protein lacking transmembrane helices. Reason: InterPro2GO maps IPR010067 (ABC_SsuA_sub-bd) to GO:0016020 (membrane) because SsuA operates with the inner-membrane SsuBC complex. However, SsuA2 possesses a cleaved N-terminal signal peptide (residues 1-29) and a soluble periplasmic binding protein-like II domain (residues 35-257, SMART SM00062) with no transmembrane segments, localizing to the outer membrane-bounded periplasmic space (GO:0030288) rather than being an integral or lipid-anchored membrane protein (GO:0016020); its association with the inner-membrane SsuC5-SsuB2 translocon as a soluble periplasmic docking subunit is captured separately via part_of GO:0055052 (ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing). Supporting Evidence: file:VARPD/ssuA2/ssuA2-uniprot.txt FT SIGNAL 1..29 FT /evidence="ECO:0000256|SAM:SignalP" file:VARPD/ssuA2/ssuA2-uniprot.txt CC -!- PTM: Predicted to be exported by the Tat system. The position of the CC signal peptide cleavage has not been experimentally proven. CC {ECO:0000256|PROSITE-ProRule:PRU00648}. |
| GO:0042597 periplasmic space | IEA GO_REF:0000044 | MODIFY | Summary: Correct but general cellular component; refine to GO:0030288 (outer membrane-bounded periplasmic space) for this Gram-negative betaproteobacterial periplasmic binding protein. Reason: SsuA2 possesses a canonical N-terminal twin-arginine translocation (Tat) signal peptide (PROSITE PS51318, PROSITE-ProRule PRU00648, residues 1-29, containing the Arg8-Arg9-Arg10 motif within 1-MTSISVPRRRLLQGAAAAAIALPSFAALA-29) followed by a soluble periplasmic binding protein-like II domain (residues 30-319, NCBIfam TIGR01728). Because Variovorax paradoxus is a diderm Gram-negative bacterium, GO:0042597 (periplasmic space) is refined to its more specific descendant GO:0030288 (outer membrane-bounded periplasmic space). Proposed replacements: outer membrane-bounded periplasmic space Supporting Evidence: file:VARPD/ssuA2/ssuA2-uniprot.txt FT SIGNAL 1..29 FT /evidence="ECO:0000256|SAM:SignalP" file:VARPD/ssuA2/ssuA2-uniprot.txt CC -!- PTM: Predicted to be exported by the Tat system. The position of the CC signal peptide cleavage has not been experimentally proven. CC {ECO:0000256|PROSITE-ProRule:PRU00648}. |
| GO:0042626 ATPase-coupled transmembrane transporter activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Over-annotated on the isolated periplasmic binding subunit; GO:0042626 describes the ATP-driven transmembrane transport activity of the intact SsuABC complex rather than the soluble SsuA2 subunit alone. Reason: InterPro2GO maps IPR010067 (ABC_SsuA_sub-bd) to GO:0042626 (ATPase-coupled transmembrane transporter activity). Because SsuA2 is a soluble periplasmic substrate-binding protein lacking transmembrane pore or ATPase domains, it cannot catalyze ATP-coupled transmembrane transport on its own; its contribution to complex-level GO:0042959 (ABC-type alkanesulfonate transporter transporter activity) is recorded via contributes_to_molecular_function in core_functions. Supporting Evidence: file:VARPD/ssuA2/ssuA2-uniprot.txt DR NCBIfam; TIGR01728; SsuA_fam; 1. PMID:10781557 The first group consists of ssuA , ssuB , and ssuC , which are the genes for a putative ATP-binding cassette (ABC)-type transport system. |
| GO:0055085 transmembrane transport | IEA GO_REF:0000108 | MODIFY | Summary: Correct but general biological process; refine to GO:0042918 (alkanesulfonate transmembrane transport) based on NCBIfam TIGR01728, PANTHER PTHR30024:SF42, and syntenic clustering in the ssu operon. Reason: GO:0055085 (transmembrane transport) is true of SsuA2 but overly general. SsuA2 belongs to the SsuA aliphatic sulfonates-binding protein family (NCBIfam TIGR01728, InterPro IPR010067, PANTHER PTHR30024:SF42) and is co-encoded in the contig JZWI01000005 ssu cluster with ssuB2 (VPARA_09230, UniProtKB:A0A0H2MBB8), ssuC5 (VPARA_09240, UniProtKB:A0A0H2M6G6), ssuD (VPARA_09250, UniProtKB:A0A0H2MCI3), and ssuE (VPARA_09290, UniProtKB:A0A0H2M6H0) to mediate alkanesulfonate transmembrane transport (GO:0042918; PMID:10781534, PMID:10781557). Proposed replacements: alkanesulfonate transmembrane transport Supporting Evidence: file:VARPD/ssuA2/ssuA2-uniprot.txt DR PANTHER; PTHR30024:SF42; ALIPHATIC SULFONATES-BINDING PROTEIN-RELATED; 1. PMID:10781534 The Escherichia coli tauABCD and ssuEADCB gene clusters are required for the utilization of taurine and alkanesulfonates as sulfur sources and are expressed only under conditions of sulfate or cysteine starvation. |
| GO:0055052 ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing | IC PMID:10781557 The ssu locus plays a key role in organosulfur metabolism in... | NEW | Summary: Periplasmic substrate-binding subunit of the tripartite SsuA2-SsuB2-SsuC5 ABC alkanesulfonate importer complex. Reason: Inferred by curator (IC) because SsuA2 (VPARA_09270, KLN57916.1) is a periplasmic substrate-binding protein (NCBIfam TIGR01728) encoded in the same contig JZWI01000005 sulfonate-utilization cluster as the ATPase subunit ssuB2 (VPARA_09230, UniProtKB:A0A0H2MBB8, KLN57912.1) and the permease subunit ssuC5 (VPARA_09240, UniProtKB:A0A0H2M6G6, KLN57913.1), functioning as part of the substrate-binding-subunit-containing ABC importer complex (GO:0055052; PMID:10781534, PMID:10781557). Supporting Evidence: file:VARPD/ssuA2/ssuA2-uniprot.txt DR EMBL; JZWI01000005; KLN57916.1; -; Genomic_DNA. PMID:10781557 The first group consists of ssuA , ssuB , and ssuC , which are the genes for a putative ATP-binding cassette (ABC)-type transport system. |
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Download this section (compressed HTML)Q: What is the substrate binding spectrum of Variovorax paradoxus SsuA2 (VPARA_09270) across linear C2-C10 alkanesulfonates, sulfonated buffers (HEPES, MOPS), and aromatic sulfonates compared with paralogous ssuA genes in V. paradoxus TBEA6?
Suggested experts: Kertesz MA, Leisinger T, Ellis HR
Experiment: Purify mature recombinant Variovorax paradoxus SsuA2 (residues 30-319, lacking the N-terminal Tat signal peptide) and determine dissociation constants for ethanesulfonate, pentanesulfonate, octanesulfonate, and taurine by isothermal titration calorimetry and intrinsic tryptophan fluorescence quenching.
Hypothesis: Mature SsuA2 binds aliphatic C2-C8 alkanesulfonates with sub-micromolar to low-micromolar affinity while discriminating against taurine and inorganic sulfate.
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