ParA (PA5563, Soj) is the ATPase of the Pseudomonas aeruginosa ParABS chromosome-partitioning system, encoded upstream of parB in the gidAB-parAB operon about 8 kb from oriC. It is a 262-residue deviant Walker-type (ParA/MinD-family) P-loop ATPase with the KGGVGKT Walker A box. Purified ParA hydrolyses ATP. ParA self-associates and binds its partner ParB through a region around residues 67-85 that overlaps the dimer interface; dimerization is needed for the ParB interaction. ParA is reported as a cytosolic protein, at about 600 molecules per cell in exponential growth. With ParB bound at the oriC-proximal parS sites, ParA drives separation of the replicated origin domains. Loss of ParA, or a ParA that cannot dimerize and bind ParB, causes anucleate cells, failure to separate ParB foci, slower growth and altered motility, and destabilises ParB. Overproduction of ParA is toxic.
IDA PMID:25139949 Dissection of the region of Pseudomonas aeruginosa ParA that...
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Summary: Purified P. aeruginosa ParA hydrolyses ATP.
Reason: Direct biochemical evidence: ParA-His6 releases phosphate from ATP at about 1.2 pmol Pi per min per pmol ParA (malachite green assay), and the dimerization and ParB-interaction mutants keep this activity. ATP hydrolysis is the core activity of the deviant Walker-type ParA ATPases, which ParB stimulates in characterized systems. GOA has no annotation of any kind for this protein. NCBI's BlastRule names it "chromosome partitioning protein Soj" but carries no GO.
IMP PMID:17545287 Deletion of the parA (soj) homologue in Pseudomonas aerugino...
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Summary: ParA is the ATPase that moves the ParB-parS origin complexes during chromosome segregation.
Reason: ParA does work in this process, as the partition ATPase that positions the ParB-parS complex. It is not merely necessary for it. The genetics are direct: parA inactivation or overexpression causes anucleate cells. A dimerization- and ParB-binding-deficient allele (parA84) fails to separate ParB foci and phenocopies the null, whereas a ParA that only loses ParB binding (parA67) is partly defective. The parA84 protein (ParA L84K) accumulates at least fivefold less than wild-type ParA, but the authors show that the ParB foci defect persists when the mutant protein is supplied at about twice the wild-type level, so it follows from the substitution rather than the low level.
IPI PMID:25139949 Dissection of the region of Pseudomonas aeruginosa ParA that...
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Summary: ParA dimerizes, and dimerization is needed for its interaction with ParB.
Reason: ParA self-association was shown by two-hybrid assays only: yeast two-hybrid deletion mapping and bacterial two-hybrid (BACTH) alanine scanning of region E67-L85. Mutants that cannot dimerize also lose ParB binding. Dimerization is not needed for ATP hydrolysis here, since the dimerization-deficient L84 mutant keeps wild-type ATPase activity. It is a supporting activity, required for the ParB interaction, not a core one.
Alanine scanning of charged and hydrophobic residues in the ParA region E67–L85 and analysis of ParA variants in the BACTH system clearly demonstrated the essentiality of this region for both ParA self-interactions and interactions with ParB.
TAS PMID:17545287 Deletion of the parA (soj) homologue in Pseudomonas aerugino...
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Summary: ParA is reported as a soluble, cytosolic protein.
Reason: The study reports ParA as a cytosolic protein (about 600 molecules per cell in exponential phase). Only the abstract is available, so the method is not known and the row is recorded as a traceable author statement rather than direct assay. Cytoplasm is proposed rather than cytosol: in other species, ParA-family ATPases associate with the nucleoid through non-specific DNA binding, and cytoplasm covers both states. Nucleoid association has not been tested in P. aeruginosa, so no nucleoid term is proposed.
IC PMID:25139949 Dissection of the region of Pseudomonas aeruginosa ParA that...
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Summary: ParA binds the ATP it hydrolyses.
Reason: Curator inference from the measured ATP hydrolysis by purified ParA, which requires ATP binding, together with the deviant Walker A box KGGVGKT at residues 11-17. Binding was not measured separately, so the code is IC. Recorded separately because GO does not derive ATP binding from ATP hydrolysis activity.
ParA-His6 demonstrated ATPase activity (Fig. 3) of ~1.2 pmol Pi released min−1 (pmol ParA)−1.
file:PSEPK/parA/parA-bioinformatics/RESULTS.md
ParA has the deviant Walker A box KGGVGKT at 11-17, the ATP-binding signature of the ParA/MinD family.
Core Functions
Deviant Walker-type ATPase of the ParABS system. ATP hydrolysis by ParA dimers, in partnership with ParB bound at oriC-proximal parS sites, moves the replicated origin domains apart.
Q: Does P. aeruginosa ParA bind DNA non-specifically in an ATP-dependent manner, as B. subtilis Soj does, and is that the basis of its nucleoid-based transport?
Q: Is P. aeruginosa ParA ATPase stimulated by ParB and by DNA, and does the ParB N-terminal motif deliver that stimulation as in Myxococcus?
Suggested Experiments
Experiment: Assay purified ParA for ATP-dependent non-specific DNA binding, and measure its ATPase rate with DNA, ParB, and both together.
Hypothesis: ParA binds DNA as an ATP-sandwich dimer and its ATPase is synergistically activated by DNA and ParB.
Type: biochemistry (EMSA and ATPase assay)
External Prediction Reviews
These computational predictions are reviewed separately from the GOA annotation set used for this review. The assessments below are from this project and do not constitute official GO annotations or endorsement by GO/UniProt. They are not included in the existing annotation review above.
P. aeruginosa PAO1 is one of NCBI's curated reference genomes, so PGAP does not annotate its assembly. The identical protein WP_003097243.1 (53,716 assemblies in its identical-protein record, 2026-10-24) is annotated by PGAP in other genomes. Unlike its 84%-identical P. putida ortholog, it is named not from a CDD architecture but from BlastRule NBR012933, "chromosome partitioning protein Soj". The BlastRule gives a more specific name than the P. putida architecture ("ParA family protein") but carries no GO, and under winner-take-all no other model passes on terms. The protein therefore gets no GO from NCBI. GOA also has none, so neither pipeline annotates this experimentally characterized ATPase. The P. putida architecture shows what the BlastRule could carry: ATP binding and ATP hydrolysis activity, both correct for this protein. The main review proposes ATP hydrolysis activity (IDA), chromosome segregation (IMP), protein homodimerization activity (IPI) and cytoplasm (IDA). There are no PGAP predictions to assess.