Periplasmic high-affinity phosphate-binding protein PstS (VPARA_10480, A0A0H2M7F6) of the PstSCAB ABC-type inorganic orthophosphate importer in Variovorax paradoxus strain TBEA6 is a 345-amino-acid precursor encoded on genomic contig JZWI01000005 (EMBL KLN58036.1) within the conserved phoR1-phoB1-phoU-pstB-pstA-pstC-pstS-ppx phosphate starvation regulon gene cluster (VPARA_10420-VPARA_10490). PstS comprises a 24-residue N-terminal Sec signal peptide (residues 1-24) that directs export across the inner membrane into the outer membrane-bounded periplasmic space, and a mature periplasmic polypeptide (residues 25-345, PRO_5002596677) folding into a two-domain Venus flytrap-type periplasmic binding protein-like II domain (Pfam PF12849, CDD cd13565, InterPro IPR005673, NCBIfam TIGR00975, PANTHER PTHR42996:SF1). PstS binds inorganic orthophosphate with submicromolar affinity in the periplasm and delivers it to the inner-membrane PstC-PstA permease channel energized by the cytoplasmic PstB ATPase dimer, while also participating with PstCAB and PhoU in sensing extracellular phosphate sufficiency to regulate the PhoR1-PhoB1 two-component system.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0035435 phosphate ion transmembrane transport | IEA GO_REF:0000002 | ACCEPT | Summary: Core biological process; PstS captures inorganic orthophosphate in the periplasm and delivers it to the PstCA inner-membrane permease channel for ATP-driven import into the cytoplasm. Reason: VPARA_10480 belongs to the canonical PstS periplasmic phosphate-binding protein family (InterPro IPR005673, NCBIfam TIGR00975, PANTHER PTHR42996:SF1) and is encoded immediately adjacent to pstC-pstA-pstB-phoU (VPARA_10440-VPARA_10470) in the V. paradoxus TBEA6 PstSCAB operon (PMID:3881386, PMID:24563032). Supporting Evidence: file:VARPD/pstS/pstS-uniprot.txt CC -!- FUNCTION: Part of the ABC transporter complex PstSACB involved in CC phosphate import. {ECO:0000256|ARBA:ARBA00002841, CC ECO:0000256|PIRNR:PIRNR002756}. PMID:24563032 PstS is the periplasmic P i -binding protein, PstC and PstA are integral membrane proteins that form the pore through which P i passes, and PstB is the dimeric, cytoplasmic ATPase. |
| GO:0042301 phosphate ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: Core molecular function of PstS via its two-domain Venus flytrap periplasmic orthophosphate-binding cleft (CDD cd13565, Pfam PF12849, InterPro IPR005673). Reason: PstS (InterPro IPR005673, CDD cd13565, PANTHER PTHR42996:SF1) directly coordinates tetrahedral inorganic orthophosphate in the cleft between its two globular periplasmic binding domains with high affinity and strict selectivity over sulfate (PMID:2215649, PMID:24563032). Supporting Evidence: file:VARPD/pstS/pstS-uniprot.txt DR InterPro; IPR005673; ABC_phos-bd_PstS. PMID:2215649 We report here the highly refined 1.7 A resolution X-ray structure of the liganded form of the phosphate-binding protein. The structure reveals the atomic features responsible for phosphate selectivity, either in monobasic or dibasic form, and the exclusion of sulphate. PMID:24563032 PstS is the periplasmic P i -binding protein, PstC and PstA are integral membrane proteins that form the pore through which P i passes, and PstB is the dimeric, cytoplasmic ATPase. |
| GO:0043190 ATP-binding cassette (ABC) transporter complex | IEA GO_REF:0000002 | MODIFY | Summary: Correct but general cellular component; refine to GO:0055052 (ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing). Reason: PstS is the periplasmic solute-binding subunit of the Type I bacterial ABC importer complex PstSCAB (composed of PstS, PstC, PstA, and a PstB dimer; PMID:3881386, PMID:24563032); refine generic GO:0043190 to its specific descendant GO:0055052 (ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing), matching ECOLI/pstS, ECOLI/pstC, ECOLI/pstA, and ECOLI/pstB. Proposed replacements: ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing Supporting Evidence: file:VARPD/pstS/pstS-uniprot.txt CC -!- SUBUNIT: The complex is composed of two ATP-binding proteins (PstB), CC two transmembrane proteins (PstC and PstA) and a solute-binding protein CC (PstS). {ECO:0000256|ARBA:ARBA00011529, ECO:0000256|PIRNR:PIRNR002756}. PMID:24563032 The Pst proteins form a type I ATP-binding cassette (ABC) importer that exhibits high-affinity, P i -specific transport ( 18 – 20 ). PstS is the periplasmic P i -binding protein, PstC and PstA are integral membrane proteins that form the pore through which P i passes, and PstB is the dimeric, cytoplasmic ATPase. |
| GO:0030288 outer membrane-bounded periplasmic space | IC file:VARPD/pstS/pstS-uniprot.txt | NEW | Summary: Core subcellular localization; Variovorax paradoxus is a diderm Betaproteobacterium and PstS carries an N-terminal signal peptide (residues 1-24) for export into the outer membrane-bounded periplasmic space. Reason: Inferred by curator (IC) from the SignalP-annotated N-terminal secretory signal peptide (residues 1-24) and mature periplasmic PBP domain (residues 25-345, Pfam PF12849) in a Gram-negative diderm Betaproteobacterium, corroborated by experimental periplasmic localization of bacterial PstS (PMID:6321434, PMID:24563032). Supporting Evidence: file:VARPD/pstS/pstS-uniprot.txt FT SIGNAL 1..24 FT /evidence="ECO:0000256|SAM:SignalP" FT CHAIN 25..345 FT /note="Phosphate-binding protein PstS" PMID:6321434 The complete nucleotide sequence of the phoS gene, the structural gene for the phosphate-repressible, periplasmic phosphate-binding protein Escherichia coli K-12, was determined. The phosphate-binding protein is synthesized in a precursor form which includes an additional N-terminal segment containing 25 amino acid residues, with the general characteristics of a signal sequence. |
| GO:0055052 ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing | IC file:VARPD/pstS/pstS-uniprot.txt | NEW | Summary: PstS is the periplasmic substrate-binding subunit of the PstSCAB ABC phosphate importer complex. Reason: Inferred by curator (IC) from the SUBUNIT annotation in file:VARPD/pstS/pstS-uniprot.txt and conserved operon architecture with pstC (VPARA_10470), pstA (VPARA_10460), and pstB (VPARA_10450) on contig JZWI01000005 (PMID:3881386, PMID:24563032). Supporting Evidence: file:VARPD/pstS/pstS-uniprot.txt CC -!- SUBUNIT: The complex is composed of two ATP-binding proteins (PstB), CC two transmembrane proteins (PstC and PstA) and a solute-binding protein CC (PstS). {ECO:0000256|ARBA:ARBA00011529, ECO:0000256|PIRNR:PIRNR002756}. PMID:24563032 The Pst proteins form a type I ATP-binding cassette (ABC) importer that exhibits high-affinity, P i -specific transport ( 18 – 20 ). PstS is the periplasmic P i -binding protein, PstC and PstA are integral membrane proteins that form the pore through which P i passes, and PstB is the dimeric, cytoplasmic ATPase. |
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Download this section (compressed HTML)Q: How do the multiple PstS paralogs encoded in the Variovorax paradoxus TBEA6 genome differ from the canonical operon-encoded PstS (VPARA_10480) in orthophosphate binding affinity, pH optimum, and ability to dock onto the PstCA (VPARA_10470/VPARA_10460) permease?
Suggested experts: McCleary WR, Quiocho FA
Experiment: Express and purify mature recombinant VPARA_10480 (residues 25-345) and measure its binding affinity and selectivity for orthophosphate, arsenate, and sulfate by isothermal titration calorimetry (ITC) across pH 5.5-8.0.
Hypothesis: Mature VPARA_10480 binds inorganic orthophosphate with submicromolar affinity and discriminates strictly against sulfate.
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