Taurine-binding periplasmic protein TauA (VPARA_03650, A0A0H2M727) in Variovorax paradoxus strain TBEA6 is a 340-amino-acid periplasmic solute-binding subunit (NCBIfam TIGR01729, InterPro IPR010068, PANTHER PTHR30024:SF47) of the TauABC ATP-binding cassette (ABC) taurine importer complex. Encoded at the 5' end of the syntenic tauA-tauB1-tauC (VPARA_03650-VPARA_03670) operon on genomic contig JZWI01000003 (consecutive EMBL CDS accessions KLN58254.1-KLN58256.1) immediately upstream of the ATPase subunit tauB1 (VPARA_03660, KLN58255.1) and the transmembrane permease tauC (VPARA_03670, KLN58256.1), TauA possesses an N-terminal signal peptide (residues 1-30) that directs export of the mature periplasmic ligand-binding domain (residues 31-340) to capture extracellular taurine (2-aminoethanesulfonate) with high specificity and deliver it to the inner-membrane TauC-TauB1 translocon for cytoplasmic desulfonation by TauD1 (VPARA_23370).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0042597 periplasmic space | IEA GO_REF:0000120 | 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: TauA contains a SignalP-predicted N-terminal signal peptide (residues 1-30, PROSITE PS51318, PROSITE-ProRule PRU00648) and a soluble periplasmic binding protein-like II domain (residues 31-340, NCBIfam TIGR01729, InterPro IPR010068). 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; PMID:8808933, PMID:17203388). Proposed replacements: outer membrane-bounded periplasmic space Supporting Evidence: file:VARPD/tauA/tauA-uniprot.txt FT SIGNAL 1..30 FT /evidence="ECO:0000256|SAM:SignalP" PMID:8808933 The TauA protein contained a putative signal peptide for transport into the periplasm; the TauB and TauC proteins showed sequence similarity to ATP-binding proteins and membrane proteins, respectively, of ABC-type transport systems |
| GO:0042918 alkanesulfonate transmembrane transport | IEA GO_REF:0000118 | MODIFY | Summary: Correct but general parent process; refine to the specific child term GO:0015734 (taurine transmembrane transport) based on NCBIfam TIGR01729, PANTHER PTHR30024:SF47, and syntenic placement in the tauA-tauB1-tauC operon. Reason: TreeGrafter (PTN001246836) annotates GO:0042918 (alkanesulfonate transmembrane transport) from the broader SsuA/TauA parent clade. TauA belongs specifically to the periplasmic taurine-binding protein family (NCBIfam TIGR01729 taurine_ABC_bnd, InterPro IPR010068, PANTHER PTHR30024:SF47 TAURINE-BINDING PERIPLASMIC PROTEIN) and is encoded at the 5' end of the tauA-tauB1-tauC (VPARA_03650-VPARA_03670) operon on contig JZWI01000003, supporting refinement to the more specific descendant term GO:0015734 (taurine transmembrane transport; PMID:8808933, PMID:10781534, PMID:17203388). Proposed replacements: taurine transmembrane transport Supporting Evidence: file:VARPD/tauA/tauA-uniprot.txt DR PANTHER; PTHR30024:SF47; TAURINE-BINDING PERIPLASMIC PROTEIN; 1. PMID:8808933 We therefore suggest that the proteins encoded by tauABC constitute an uptake system for taurine and that the product of tauD is involved in the oxygenolytic release of sulfite from taurine. |
| GO:0030977 taurine binding | ISS PMID:17203388 Functional characteristics of TauA binding protein from TauA... | NEW | Summary: Intrinsic molecular function capturing high-affinity periplasmic binding of taurine (2-aminoethanesulfonate). Reason: Purified bacterial TauA (NCBIfam TIGR01729, InterPro IPR010068, PANTHER PTHR30024:SF47) binds taurine with high affinity (Kd = 11.3 nM) and specificity at a single periplasmic ligand-binding site (PMID:17203388); GO:0030977 (taurine binding) captures TauA's intrinsic ligand-binding activity while its complex-level contribution to GO:0015411 (ABC-type taurine transporter transporter activity) is recorded via contributes_to_molecular_function in core_functions. Supporting Evidence: file:VARPD/tauA/tauA-uniprot.txt DR NCBIfam; TIGR01729; taurine_ABC_bnd; 1. PMID:17203388 Measurement of K (d) value (mean 11.3 nM) by binding/dialysis studies revealed high affinity and specificity with taurine and also indicated that TauA possessed a unique binding site for its ligand. |
| GO:0055052 ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing | IC PMID:8808933 Identification of sulfate starvation-regulated genes in Esch... | NEW | Summary: Periplasmic substrate-binding subunit of the tripartite TauA-TauB1-TauC ABC taurine importer complex. Reason: Inferred by curator (IC) because TauA (VPARA_03650, KLN58254.1) is encoded immediately upstream of the ATPase subunit tauB1 (VPARA_03660, UniProtKB:A0A0H2MNF8, KLN58255.1) and the transmembrane permease tauC (VPARA_03670, UniProtKB:A0A0H2M7Y1, KLN58256.1) on contig JZWI01000003, assembling into the substrate-binding-subunit-containing TauABC importer complex (GO:0055052; PMID:8808933, PMID:10781534). Supporting Evidence: file:VARPD/tauA/tauA-uniprot.txt DR EMBL; JZWI01000003; KLN58254.1; -; Genomic_DNA. PMID:8808933 We therefore suggest that the proteins encoded by tauABC constitute an uptake system for taurine and that the product of tauD is involved in the oxygenolytic release of sulfite from taurine. |
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Download this section (compressed HTML)Q: Does Variovorax paradoxus TauA (VPARA_03650) bind hypotaurine or isethionate in addition to taurine, and is the unlinked tauA-tauB1-tauC (VPARA_03650-VPARA_03670) operon co-regulated by CysB with the unlinked taurine dioxygenase tauD1 (VPARA_23370) under sulfate starvation?
Suggested experts: Kertesz MA, Leisinger T
Experiment: Purify mature Variovorax paradoxus TauA (residues 31-340) and measure its binding affinity for taurine, hypotaurine, and ethanesulfonate by isothermal titration calorimetry.
Hypothesis: Mature V. paradoxus TauA binds taurine with nanomolar affinity at a single binding site and strongly discriminates against unsubstituted alkanesulfonates.
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