Curatorial Notes for `pstS` (`A0A0H2M7F6`, `VPARA_10480`) in Variovorax paradoxus TBEA6

1. Gene & Protein Identity

UniProt Accession: A0A0H2M7F6 (A0A0H2M7F6_VARPD)
Gene Symbol: pstS
Locus Tag / EMBL CDS: VPARA_10480 / KLN58036.1 on contig JZWI01000005 (RefSeq:WP_047783563.1)
Protein Length: 345 aa (36,423 Da); N-terminal SignalP cleavable secretory signal peptide at residues 1–24 (MKTTFKFAAAGLVAAAFAHVPAFA), mature periplasmic chain at residues 25–345 (PRO_5002596677), Type-II periplasmic binding protein (PBP) domain at residues 26–304 (Pfam:PF12849 PBP_like_2).
Family & Domain Architecture:
InterPro:IPR005673 (ABC_phos-bd_PstS), InterPro:IPR024370 (PBP_domain), InterPro:IPR050962 (PstS-like)
CDD:cd13565 (PBP2_PstS), NCBIfam:TIGR00975 (3a0107s03), NCBIfam:NF008171 (pstS), PIRSF:PIRSF002756 (PstS)
PANTHER:PTHR42996:SF1 (PHOSPHATE-BINDING PROTEIN PSTS)

pstS (VPARA_10480, KLN58036.1) lies immediately adjacent to the high-affinity phosphate transport and PhoBR two-component regulatory gene cluster on contig JZWI01000005:
VPARA_10420 (KLN58030.1, phoR1, A0A0H2MMT2): Phosphate regulon sensor histidine kinase PhoR1 (464 aa)
VPARA_10430 (KLN58031.1, phoB1, A0A0H2M7F4): Phosphate regulon response regulator PhoB1 (230 aa)
VPARA_10440 (KLN58032.1, phoU, A0A0H2MBK2): Phosphate-specific transport system accessory regulatory protein PhoU (233 aa)
VPARA_10450 (KLN58033.1, pstB, A0A0D0L7E0): Phosphate import ATP-binding protein PstB (259 aa)
VPARA_10460 (KLN58034.1, pstA, A0A0H2M6I3): Phosphate transport system permease protein PstA (294 aa)
VPARA_10470 (KLN58035.1, pstC, A0A0H2MMT5): Phosphate transport system permease protein PstC (359 aa)
VPARA_10480 (KLN58036.1, pstS, A0A0H2M7F6): Periplasmic phosphate-binding protein PstS (345 aa)
VPARA_10490 (KLN58037.1, ppx, A0A0H2MBK5): Exopolyphosphatase Ppx (506 aa, curated in Tranche 3)

PMID:2215649 (Luecke & Quiocho 1990 Nature): 1.7 Å crystal structure of E. coli periplasmic phosphate-binding protein PstS showing how the hinged two-domain cleft coordinates tetrahedral orthophosphate via 12 hydrogen bonds and an aspartate carboxylate that confers strict selectivity against sulfate.
PMID:6321434 (Surin et al. 1984 J Bacteriol) and PMID:3881386 (Surin et al. 1985 J Bacteriol): Sequence and organization of phoS (pstS) and the pstS-pstC-pstA-pstB-phoU operon in E. coli, establishing export of PstS to the periplasm via a cleavable N-terminal signal sequence.
PMID:24563032 (Gardner et al. 2014 J Bacteriol): Synthesizes the mechanism of the PstSCAB-PhoU-PhoRB complex in high-affinity $\text{P}_i$ uptake and $\text{P}_i$-sufficiency signaling.

GO:0042301 (phosphate ion binding, IEA GO_REF:0000002): ACCEPT — core molecular function of periplasmic PstS (with contributes_to_molecular_function: GO:0015415 ATPase-coupled phosphate ion transmembrane transporter activity on core_functions).
GO:0035435 (phosphate ion transmembrane transport, IEA GO_REF:0000002): ACCEPT — core biological process; PstS captures orthophosphate in the periplasm and delivers it to the PstCA permease channel.
GO:0043190 (ATP-binding cassette (ABC) transporter complex, IEA GO_REF:0000002): MODIFY -> GO:0055052 (ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing) — refines the generic ABC transporter complex term to the specific child complex that includes the periplasmic substrate-binding subunit (matching ECOLI/pstS, ECOLI/pstC, ECOLI/pstA, ECOLI/pstB).
GO:0030288 (outer membrane-bounded periplasmic space, IC from file:VARPD/pstS/pstS-uniprot.txt): NEW — V. paradoxus is a diderm Betaproteobacterium and VPARA_10480 carries a canonical 24-aa SignalP signal peptide (FT SIGNAL 1..24) for export of mature PstS (25..345) to the outer membrane-bounded periplasmic space.
GO:0055052 (ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing, IC from file:VARPD/pstS/pstS-uniprot.txt): NEW — asserted alongside the modified GO:0043190 row.