cysNC

UniProt ID: Q88NA8
Organism: Pseudomonas putida (strain ATCC 47054 / DSM 6125 / CFBP 8728 / NCIMB 11950 / KT2440)
Review Status: DRAFT
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Gene Description

CysNC is the GTPase-containing regulatory subunit 1 of the proteobacterial sulfate adenylyltransferase complex. It couples GTP hydrolysis to the CysD reaction that converts sulfate and ATP to APS. The protein also carries a C-terminal APS-kinase-like domain, but the catalytic contribution of that domain to the KT2440 complex remains unresolved.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0000103 sulfate assimilation
IEA
GO_REF:0000104 		ACCEPT
Summary: Correct pathway assignment for the regulatory ATP sulfurylase subunit.
Reason: CysNC is required for energy-coupled APS formation in sulfate assimilation.
GO:0003924 GTPase activity
IEA
GO_REF:0000120 		ACCEPT
Summary: Correct subunit-specific molecular function.
Reason: CysN-family regulatory subunits hydrolyze GTP to drive the otherwise unfavorable sulfate-adenylation reaction.
Supporting Evidence:
file:PSEPK/cysNC/cysNC-uniprot.txt
GTP hydrolysis by CysN coupled
GO:0004781 sulfate adenylyltransferase (ATP) activity
IEA
GO_REF:0000120 		MODIFY
Summary: Correct complex-level activity, but the imported enables qualifier incorrectly assigns the CysD-catalyzed reaction to CysNC itself.
Reason: Q88NA8 is required in the physiological ATP sulfurylase complex, but its subunit-specific catalytic activity is GTP hydrolysis. Retain GO:0004781 with contributes_to rather than enables.
Supporting Evidence:
file:PSEPK/cysNC/cysNC-uniprot.txt
With CysD forms the ATP sulfurylase (ATPS) that catalyzes the
GO:0005525 GTP binding
IEA
GO_REF:0000120 		KEEP AS NON CORE
Summary: Correct supporting nucleotide-binding property.
Reason: GTPase activity captures the functional consequence of GTP binding.
GO:0006790 sulfur compound metabolic process
IEA
GO_REF:0000002 		MARK AS OVER ANNOTATED
Summary: Correct but excessively broad process parent.
Reason: GO:0000103 identifies the relevant sulfate-assimilation process.
GO:0070814 hydrogen sulfide biosynthetic process
IEA
GO_REF:0000120 		ACCEPT
Summary: Correct downstream process assignment.
Reason: CysNC-dependent APS formation initiates the sulfate-to-sulfide route.

Core Functions

Hydrolyzes GTP as the regulatory subunit of the CysD/CysNC ATP sulfurylase, coupling GTP turnover to sulfate adenylation.

Molecular Function:
GTPase activity
Directly Involved In:
sulfate assimilation
Supporting Evidence:
  • file:PSEPK/cysNC/cysNC-uniprot.txt
    GTP hydrolysis by CysN coupled
  • PMID:16387658
    coupling the energy of GTP hydrolysis to APS formation.

References

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Suggested Questions for Experts

Q: Is the C-terminal APS-kinase-like domain of Q88NA8 catalytically active, or is it a retained but inactive fusion remnant in the direct APS-reduction route?

Suggested Experiments

Experiment: Reconstitute Q88NA8/Q88NA9 and quantify both APS and PAPS formation, then test isolated C-terminal-domain and active-site variants for APS kinase activity.

Type: pathway reconstitution and domain-function assay

📚 Additional Documentation

Notes

(cysNC-notes.md)

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