carA

UniProt ID: Q88DU5
Organism: Pseudomonas putida KT2440
Review Status: DRAFT
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Gene Description

carA encodes the glutaminase small chain of carbamoyl-phosphate synthase. It hydrolyzes glutamine and channels ammonia to CarB for ATP-dependent carbamoyl-phosphate formation serving both de novo UMP and L-arginine biosynthesis.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0004088 carbamoyl-phosphate synthase (glutamine-hydrolyzing) activity
IEA
GO_REF:0000120 		REMOVE
Summary: CarA supplies the glutaminase component of the two-chain glutamine-dependent carbamoyl-phosphate synthase.
Reason: The enables relation is incorrect because CarA contributes its glutaminase reaction to the overall two-chain activity; it does not catalyze the complete glutamine-dependent synthesis reaction alone. A separate contributes_to row captures the supported relation.
Supporting Evidence:
file:PSEPK/carA/carA-uniprot.txt
Small subunit of the glutamine-dependent carbamoyl phosphate
GO:0004088 carbamoyl-phosphate synthase (glutamine-hydrolyzing) activity
ISS
file:PSEPK/carA/carA-uniprot.txt 		NEW
Summary: CarA contributes the glutaminase component of the two-chain CarAB activity.
Reason: CarA hydrolyzes glutamine and supplies ammonia to CarB, so its relationship to the complete glutamine-dependent synthase activity is contributes_to.
Supporting Evidence:
file:PSEPK/carA/carA-uniprot.txt
Small subunit of the glutamine-dependent carbamoyl phosphate
GO:0004359 glutaminase activity
IEA
GO_REF:0000116 		ACCEPT
Summary: CarA hydrolyzes glutamine to glutamate and ammonium.
Reason: Rhea 15889 in the reviewed record directly defines this small-chain reaction.
Supporting Evidence:
file:PSEPK/carA/carA-uniprot.txt
Reaction=L-glutamine + H2O = L-glutamate + NH4(+);
file:PSEPK/carA/carA-deep-research-openscientist.md
of *Pseudomonas putida* KT2440 encodes the **small glutaminase subunit of carbamoyl phosphate synthetase (EC 6.3.5.5)**
GO:0005524 ATP binding
IEA
GO_REF:0000104 		REMOVE
Summary: ATP is consumed by the CarB large chain, not by the CarA glutaminase chain.
Reason: CarA contains the glutaminase domain and its assigned component reaction is ATP-independent; this electronic transfer conflates the two subunits.
Supporting Evidence:
file:PSEPK/carB/carB-uniprot.txt
The large subunit is composed of 2 ATP-grasp domains that are
GO:0006207 'de novo' pyrimidine nucleobase biosynthetic process
IEA
GO_REF:0000002 		MARK AS OVER ANNOTATED
Summary: CarA contributes carbamoyl phosphate to de novo pyrimidine synthesis.
Reason: The more specific de novo UMP biosynthetic process is present and preferred.
Supporting Evidence:
file:PSEPK/carA/carA-uniprot.txt
PATHWAY: Pyrimidine metabolism; UMP biosynthesis via de novo pathway;
GO:0006526 L-arginine biosynthetic process
IEA
GO_REF:0000120 		ACCEPT
Summary: The shared CarAB carbamoyl-phosphate synthase supplies the arginine pathway.
Reason: The reviewed record explicitly assigns the arginine biosynthesis branch.
Supporting Evidence:
file:PSEPK/carA/carA-uniprot.txt
PATHWAY: Amino-acid biosynthesis; L-arginine biosynthesis; carbamoyl
GO:0006541 L-glutamine metabolic process
IEA
GO_REF:0000002 		MARK AS OVER ANNOTATED
Summary: CarA directly hydrolyzes glutamine, but this broad process does not capture the biosynthetic purpose of the reaction.
Reason: Glutamine is a substrate of the reaction, but this broad process obscures the biosynthetic roles in UMP and arginine production.
Supporting Evidence:
file:PSEPK/carA/carA-uniprot.txt
Reaction=L-glutamine + H2O = L-glutamate + NH4(+);
GO:0044205 'de novo' UMP biosynthetic process
IEA
GO_REF:0000120 		ACCEPT
Summary: CarA contributes the first reaction of de novo UMP biosynthesis.
Reason: The reviewed record explicitly assigns this pathway branch.
Supporting Evidence:
file:PSEPK/carA/carA-uniprot.txt
PATHWAY: Pyrimidine metabolism; UMP biosynthesis via de novo pathway;
GO:0005951 carbamoyl-phosphate synthase complex
ISS
file:PSEPK/carA/carA-uniprot.txt 		NEW
Summary: CarA is the glutaminase chain of the two-chain carbamoyl-phosphate synthase complex.
Reason: The reviewed record explicitly describes the enzyme as a two-chain complex.
Supporting Evidence:
file:PSEPK/carA/carA-uniprot.txt
Composed of two chains; the small (or glutamine) chain

Core Functions

CarA hydrolyzes glutamine and channels ammonia to CarB in the two-chain carbamoyl-phosphate synthase.

Molecular Function:
glutaminase activity
Directly Involved In:
'de novo' UMP biosynthetic process L-arginine biosynthetic process
In Complex:
carbamoyl-phosphate synthase complex
Supporting Evidence:
  • file:PSEPK/carA/carA-uniprot.txt
    Reaction=L-glutamine + H2O = L-glutamate + NH4(+);
  • file:PSEPK/carA/carA-uniprot.txt
    Composed of two chains; the small (or glutamine) chain
  • file:PSEPK/carA/carA-deep-research-openscientist.md
    of *Pseudomonas putida* KT2440 encodes the **small glutaminase subunit of carbamoyl phosphate synthetase (EC 6.3.5.5)**

References

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Suggested Questions for Experts

Q: How tightly is ammonia transfer from CarA coupled to the two ATP-dependent partial reactions on CarB in the KT2440 heterodimer?

Suggested Experiments

Experiment: Co-express KT2440 CarA and CarB, compare glutamine-dependent and ammonia-dependent carbamoyl-phosphate synthesis, and test a CarA Cys269 substitution to verify glutaminase coupling and ammonia channeling.

Type: biochemical reconstitution assay

Deep Research

OpenScientist

(carA-deep-research-openscientist.md)

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