Curation Notes for ssuB2 (VPARA_09230, A0A0H2MBB8) in Variovorax paradoxus TBEA6

1. Gene & Protein Overview

• UniProtKB Accession: A0A0H2MBB8 (A0A0H2MBB8_VARPD, unreviewed, 276 aa, 29,405 Da)
• Gene Symbol / Locus Tag: ssuB2 / VPARA_09230 (EMBL:KLN57912.1 on genomic contig JZWI01000005, RefSeq:WP_021006427.1)
• Organism: Variovorax paradoxus strain TBEA6 (NCBITaxon:34073)
• Genomic Context: Encoded at the 5' end of the aliphatic sulfonate uptake and desulfonation gene cluster on contig JZWI01000005 immediately upstream of ssuC5 (VPARA_09240, KLN57913.1) and ssuD (VPARA_09250, KLN57914.1), with ssuA2 (VPARA_09270, KLN57916.1) and ssuE (VPARA_09290, KLN57918.1) immediately downstream.
• Domain Architecture & Key Motifs:
• ABC transporter ATP-binding domain (PROSITE:PS50893, Pfam:PF00005, InterPro:IPR003439, residues 19..240).
• PANTHER subfamily PTHR42788:SF17 (ALIPHATIC SULFONATES IMPORT ATP-BINDING PROTEIN SSUB) and InterPro:IPR005893 (Lipoprotein_rel_SsuB).
• Conserved Walker A / P-loop nucleotide-binding motif at residues 51..58 (51-GRSGCGKS-58, FT BINDING 51..58 /ligand="ATP").

2. Literature & Comparative Evidence

• PMID:10781534(https://pubmed.ncbi.nlm.nih.gov/10781534/) (Eichhorn, van der Ploeg & Leisinger 2000, J Bacteriol 182:2687-2695): Deletion and complementation analysis of the E. coli ssuEADCB and tauABCD clusters demonstrated that SsuABC mediates aliphatic sulfonate uptake and that its subunits cannot form functional hybrid transporters with TauABC.
• PMID:10781557(https://pubmed.ncbi.nlm.nih.gov/10781557/) (Kahnert et al. 2000, J Bacteriol 182:2869-2878): Identified ssuA, ssuB, and ssuC in P. putida S-313 as the three subunits of the ABC-type sulfonate transporter ("The first group consists of ssuA , ssuB , and ssuC , which are the genes for a putative ATP-binding cassette (ABC)-type transport system.").

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:UR000078916) -> ACCEPT:
2. Core cofactor/substrate-binding activity of the ABC nucleotide-binding domain (PROSITE:PS50893, residues 19..240), supported by the conserved Walker A motif 51-GRSGCGKS-58 (FT BINDING 51..58).
3. GO:0016887 (ATP hydrolysis activity, enables, IEA GO_REF:0000120 from InterPro:IPR003439, PANTHER:PTN002531750, UniRule:UR000078916) -> ACCEPT:
4. Core intrinsic catalytic activity of the SsuB2 ABC ATPase subunit, which hydrolyzes ATP to energize conformational cycling of the SsuC5 transmembrane permease.
5. GO:0055085 (transmembrane transport, involved_in, IEA GO_REF:0000118 from PANTHER:PTN002531750) -> MODIFY to GO:0042918 (alkanesulfonate transmembrane transport):
6. Following the PSEPK/ssuB comparator convention, GO:0055085 is true but overly general; membership in PANTHER:PTHR42788:SF17 (ALIPHATIC SULFONATES IMPORT ATP-BINDING PROTEIN SSUB) and syntenic co-localization with ssuC5 (VPARA_09240), ssuD (VPARA_09250), ssuA2 (VPARA_09270), and ssuE (VPARA_09290) on contig JZWI01000005 support refining the biological process to GO:0042918 (alkanesulfonate transmembrane transport).

4. Proposed New Annotations

• GO:0005886 (plasma membrane, located_in, IC from file:VARPD/ssuB2/ssuB2-uniprot.txt) -> NEW:
• As the cytoplasmic-face peripheral inner-membrane ATPase subunit (CC -!- SUBCELLULAR LOCATION: Cell inner membrane {ECO:0000256|ARBA:ARBA00004190, ECO:0000256|RuleBase:RU363044}; Peripheral membrane protein) associated with the integral inner-membrane permease SsuC5, SsuB2 localizes to the plasma membrane (GO:0005886).
• GO:0055052 (ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing, part_of, IC from file:VARPD/ssuB2/ssuB2-uniprot.txt) -> NEW:
• SsuB2 (VPARA_09230, KLN57912.1) assembles with the permease ssuC5 (VPARA_09240, KLN57913.1) and periplasmic binding protein ssuA2 (VPARA_09270, KLN57916.1) into the SsuABC importer complex (GO:0055052) and contributes to complex-level GO:0042959 (ABC-type alkanesulfonate transporter transporter activity).