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CTPS2 regulates CTP synthetase activity by interacting with CTPS1.

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Cytidine triphosphate (CTP) synthetases 1 and 2 (CTPS1 and CTPS2) interact and form complexes, influencing each other's activity. These interactions are independent of cytoophidia formation, suggesting a novel regulatory mechanism for CTP synthesis.

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Cell Biology

Background:

  • Cytidine triphosphate synthetases (CTPS) 1 and 2 are crucial for de novo CTP nucleotide production, essential for DNA replication and cell proliferation.
  • CTPS1 and CTPS2 are co-expressed, share structural homology, and form enzymatically active homotetramers that aggregate into cytoophidia.
  • The role of cytoophidia in cell proliferation and the interaction between CTPS1 and CTPS2 remain incompletely understood.

Purpose of the Study:

  • To investigate the co-localization, interaction, and functional relationship between CTPS1 and CTPS2.
  • To determine the necessity of cytoophidia formation for cell proliferation.
  • To elucidate the impact of CTPS2 on CTPS1 enzymatic activity and feedback regulation.

Main Methods:

  • Co-expression of CTPS1 and CTPS2 to observe co-localization within cytoophidia.
  • Expression of catalytically inactive CTPS1 and CTPS2 mutants (CTPS1H355A, CTPS2H355A) to assess cytoophidia necessity for proliferation.
  • Co-immunoprecipitation assays to detect direct interaction between CTPS1 and CTPS2.
  • Enzyme activity assays to measure CTPS1 activity in the presence of CTPS2 and CTP/product feedback inhibition.

Main Results:

  • CTPS1 and CTPS2 co-localized in cytoophidia, with CTPS2 filament formation dependent on CTPS1 expression.
  • Cytoophidia formation is not essential for cell proliferation, as demonstrated by the sustained proliferation of CTPS1H355A and CTPS2H355A mutants.
  • CTPS1 and CTPS2 directly interact independent of polymerization and cytoophidia formation.
  • CTPS2 association decreases CTPS1 enzymatic activity and increases its sensitivity to CTP/product feedback inhibition, indicating modulation of CTPS activity by CTPS2.

Conclusions:

  • CTPS1 and CTPS2 interact directly, forming complexes that modulate enzymatic activity and feedback regulation, independent of cytoophidia.
  • Cytoophidia are dispensable for cell proliferation, suggesting alternative mechanisms for CTP synthesis regulation.
  • The findings suggest that CTPS1 and CTPS2 can directly regulate each other through heterotetramerization, revealing a novel layer of CTP metabolism control.