Curation Notes for tauB1 (VPARA_03660, A0A0H2MNF8) in Variovorax paradoxus TBEA6

1. Gene & Protein Overview

• UniProtKB Accession: A0A0H2MNF8 (A0A0H2MNF8_VARPD, unreviewed, 262 aa, 28,284 Da)
• Gene Symbol / Locus Tag: tauB1 / VPARA_03660 (EMBL:KLN58255.1 on genomic contig JZWI01000003, RefSeq:WP_021006826.1)
• Organism: Variovorax paradoxus strain TBEA6 (NCBITaxon:34073)
• Genomic Context: Encoded as the middle gene of the three-gene tauA-tauB1-tauC (VPARA_03650-VPARA_03670) taurine ABC importer operon on contig JZWI01000003 (KLN58254.1, KLN58255.1, KLN58256.1).
• Domain Architecture & Key Motifs:
• ABC transporter ATP-binding domain (PROSITE:PS50893, Pfam:PF00005, InterPro:IPR003439, residues 6..235).
• Specific subfamily: PANTHER:PTHR42788:SF18 (TAURINE IMPORT ATP-BINDING PROTEIN TAUB), InterPro:IPR005889 (TauB).
• Conserved Walker A / P-loop ATP-binding motif at residues 40..47 (40-GASGCGKT-47, FT BINDING 40..47 /ligand="ATP").

2. Literature & Comparative Evidence

• PMID:8808933(https://pubmed.ncbi.nlm.nih.gov/8808933/) (van der Ploeg et al. 1996, J Bacteriol 178:5438-5446): Identified tauB within the E. coli tauABCD operon as the ATP-binding subunit of the taurine ABC uptake system required for utilizing taurine as a sulfur source.
• PMID:10781534(https://pubmed.ncbi.nlm.nih.gov/10781534/) (Eichhorn, van der Ploeg & Leisinger 2000, J Bacteriol 182:2687-2695): In-frame deletion and complementation analysis in E. coli confirmed that tauABC is required for taurine uptake and its subunits cannot form functional hybrid transporters with ssuABC.

3. Review of Existing GOA Annotations (3 IEA rows)

1. GO:0005524 (ATP binding, enables, IEA GO_REF:0000120 from PROSITE-ProRule:PRU00434, InterPro:IPR003439, UniRule:UR000078649) -> ACCEPT:
2. Core nucleotide-binding activity of the ABC ATPase domain (PROSITE:PS50893, residues 6..235), anchored by the Walker A motif 40-GASGCGKT-47 (FT BINDING 40..47).
3. GO:0016887 (ATP hydrolysis activity, enables, IEA GO_REF:0000120 from InterPro:IPR003439, PANTHER:PTN002531845, UniRule:UR000078649) -> ACCEPT:
4. Core intrinsic catalytic activity of the TauB1 subunit, which hydrolyzes ATP to power conformational cycling of the TauC transmembrane permease.
5. GO:0055085 (transmembrane transport, involved_in, IEA GO_REF:0000118 from PANTHER:PTN002531845) -> MODIFY to GO:0015734 (taurine transmembrane transport):
6. Following the PSEPK/tauB comparator convention, GO:0055085 is true but general; membership in PANTHER:PTHR42788:SF18 (TAURINE IMPORT ATP-BINDING PROTEIN TAUB), InterPro:IPR005889 (TauB), and syntenic placement between tauA (VPARA_03650, KLN58254.1) and tauC (VPARA_03670, KLN58256.1) on contig JZWI01000003 support refinement to GO:0015734 (taurine transmembrane transport).

4. Proposed New Annotations

• GO:0005886 (plasma membrane, located_in, IC from file:VARPD/tauB1/tauB1-uniprot.txt) -> NEW:
• Peripheral inner-membrane ATP-coupling subunit (CC -!- SUBCELLULAR LOCATION: Cell inner membrane {ECO:0000256|ARBA:ARBA00004190, ECO:0000256|RuleBase:RU363042}; Peripheral membrane protein) bound to the cytoplasmic face of the TauC transmembrane permease at the plasma membrane (GO:0005886).
• GO:0055052 (ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing, part_of, IC from file:VARPD/tauB1/tauB1-uniprot.txt and PMID:8808933) -> NEW:
• TauB1 (VPARA_03660, KLN58255.1) assembles with tauA (VPARA_03650, KLN58254.1) and tauC (VPARA_03670, KLN58256.1) into the TauABC importer complex (GO:0055052), contributing to complex-level GO:0015411 (ABC-type taurine transporter transporter activity).