Phosphate transport system permease protein PstA (VPARA_10460, A0A0H2M6I3) is a 294-amino-acid six-pass inner-membrane subunit of the high-affinity PstSCAB ABC orthophosphate importer in Variovorax paradoxus strain TBEA6, encoded on genomic contig JZWI01000005 (EMBL KLN58034.1) between pstC (VPARA_10470) and pstB (VPARA_10450) within the phoR1-phoB1-phoU-pstB-pstA-pstC-pstS-ppx cluster (VPARA_10420-VPARA_10490). PstA comprises six transmembrane alpha-helices (residues 30-51, 79-102, 123-144, 150-169, 205-223, and 267-289) forming a MetI-like type-1 ABC transmembrane domain (PROSITE PS50928, Pfam PF00528, CDD cd06261, InterPro IPR005672, NCBIfam TIGR00974, NCBIfam NF008430, PANTHER PTHR42922:SF1) and conserves the essential transmembrane Arg220 and Glu224 residues (within 219-ARIAGETA-226, corresponding to E. coli PstA Arg220) required for orthophosphate translocation. PstA heterodimerizes with PstC in the plasma membrane to form the transmembrane phosphate translocation pore gated by periplasmic PstS and powered by the cytoplasmic PstB ATPase dimer.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005315 phosphate transmembrane transporter activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: PstA is one of two heterodimeric transmembrane permease subunits of the PstSCAB complex; it contributes to holocomplex phosphate transmembrane transporter activity rather than independently enabling it. Reason: Following the curation convention for ECOLI/pstA (UniProtKB:P0AGH5) and ECOLI/pstC (UniProtKB:P0AGH8), PstA is an essential transmembrane subunit of the PstSCAB importer (PMID:2896188, PMID:24563032), but GO:0005315 is enabled by the assembled PstSCAB complex rather than by PstA alone. PstA's contribution to the holocomplex ATPase-coupled phosphate ion transmembrane transporter activity (GO:0015415) is captured via contributes_to_molecular_function in core_functions. Supporting Evidence: file:VARPD/pstA/pstA-uniprot.txt DR InterPro; IPR005672; Phosphate_PstA. DR InterPro; IPR051408; Phosphate_transprt_permease. DR NCBIfam; TIGR00974; 3a0107s02c; 1. DR NCBIfam; NF008430; pstA; 1. DR PANTHER; PTHR42922; PHOSPHATE TRANSPORT SYSTEM PERMEASE PROTEIN PSTA; 1. |
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | ACCEPT | Summary: Core subcellular localization of this six-pass inner-membrane ABC permease subunit. Reason: PstA contains six transmembrane helices (residues 30-51, 79-102, 123-144, 150-169, 205-223, and 267-289; RuleBase RU363043, PROSITE PS50928) embedded in the bacterial inner (plasma) membrane (PMID:2896188, PMID:24563032). Supporting Evidence: file:VARPD/pstA/pstA-uniprot.txt CC -!- SUBCELLULAR LOCATION: Cell inner membrane CC {ECO:0000256|RuleBase:RU363043}; Multi-pass membrane protein CC {ECO:0000256|RuleBase:RU363043}. |
| GO:0016020 membrane | IEA GO_REF:0000120 | TOO GENERAL | Summary: True but uninformative parent cellular component already entailed by the accepted specific child term GO:0005886 (plasma membrane). Reason: GO:0016020 (membrane) is a broad ancestor term that adds no specificity beyond GO:0005886 (plasma membrane) already accepted in this review. Supporting Evidence: file:VARPD/pstA/pstA-uniprot.txt CC -!- SUBCELLULAR LOCATION: Cell inner membrane CC {ECO:0000256|RuleBase:RU363043}; Multi-pass membrane protein CC {ECO:0000256|RuleBase:RU363043}. |
| GO:0035435 phosphate ion transmembrane transport | IEA GO_REF:0000002 | ACCEPT | Summary: Core biological process; PstA partners with PstC to form the inner-membrane orthophosphate translocation pathway of the PstSCAB ABC importer. Reason: VPARA_10460 belongs to the canonical PstA phosphate permease family (InterPro IPR005672, NCBIfam TIGR00974, NCBIfam NF008430, PANTHER PTHR42922:SF1), conserves the essential transmembrane Arg220 residue (within 219-ARIAGETA-226, corresponding to E. coli Arg220; PMID:2896188), and is encoded between pstC and pstB in the V. paradoxus TBEA6 PstSCAB operon (PMID:3881386, PMID:24563032). Supporting Evidence: file:VARPD/pstA/pstA-uniprot.txt DR InterPro; IPR005672; Phosphate_PstA. DR InterPro; IPR051408; Phosphate_transprt_permease. DR NCBIfam; TIGR00974; 3a0107s02c; 1. DR NCBIfam; NF008430; pstA; 1. PMID:2896188 The Arg-220----Gln mutation resulted in the loss of phosphate transport through the phosphate-specific transport system, but the alkaline phosphatase activity remained repressed. |
| GO:0043190 ATP-binding cassette (ABC) transporter complex | IEA GO_REF:0000104 | MODIFY | Summary: Correct but general cellular component; refine to GO:0055052 (ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing). Reason: PstA is a transmembrane permease subunit of the binding-protein-dependent PstSCAB ABC importer complex (PMID:3881386, PMID:24563032); refine GO:0043190 to its specific child GO:0055052. Proposed replacements: ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing Supporting Evidence: file:VARPD/pstA/pstA-uniprot.txt CC -!- SIMILARITY: Belongs to the binding protein-dependent transport system CC permease family. CysTW subfamily. {ECO:0000256|ARBA:ARBA00096335, CC ECO:0000256|RuleBase:RU363043}. 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:0055085 transmembrane transport | IEA GO_REF:0000002 | TOO GENERAL | Summary: True but uninformative parent biological process already entailed by the accepted specific child term GO:0035435 (phosphate ion transmembrane transport). Reason: GO:0055085 (transmembrane transport) is a broad ancestor term that adds no specificity beyond GO:0035435 (phosphate ion transmembrane transport) already accepted in this review. Supporting Evidence: file:VARPD/pstA/pstA-uniprot.txt DR InterPro; IPR005672; Phosphate_PstA. |
| GO:0055052 ATP-binding cassette (ABC) transporter complex, substrate-binding subunit-containing | IC file:VARPD/pstA/pstA-uniprot.txt | NEW | Summary: PstA is an integral transmembrane permease subunit of the substrate-binding-protein-dependent PstSCAB ABC importer complex. Reason: Inferred by curator (IC) from RuleBase RU363043 and co-localization in the VPARA_10450-VPARA_10480 (pstB-pstA-pstC-pstS) operon (PMID:3881386, PMID:24563032). Supporting Evidence: file:VARPD/pstA/pstA-uniprot.txt CC -!- SIMILARITY: Belongs to the binding protein-dependent transport system CC permease family. CysTW subfamily. {ECO:0000256|ARBA:ARBA00096335, CC ECO:0000256|RuleBase:RU363043}. 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. |
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Download this section (compressed HTML)Q: How do the symmetric Arg276/Glu280 residues of PstC (VPARA_10470) and Arg220/Glu224 residues of PstA (VPARA_10460) coordinate tetrahedral orthophosphate halfway across the inner-membrane translocation pathway?
Suggested experts: McCleary WR
Experiment: Generate an Arg220Gln point mutation in VPARA_10460 (pstA) in Variovorax paradoxus TBEA6 and measure [32P]orthophosphate uptake rates and PhoB1 regulon transcription under high- and low-phosphate growth conditions.
Hypothesis: The Arg220Gln substitution abolishes high-affinity orthophosphate transport through PstSCAB while retaining PhoU-mediated repression of PhoR1-PhoB1 in phosphate-replete medium (PMID:2896188).
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