Large-scale filament formation inhibits the activity of CTP synthetase
Rachael M Barry,
Anne-Florence Bitbol,
Alexander Lorestani,
Emeric J Charles,
Chris H Habrian,
Jesse M Hansen,
Hsin-Jung Li,
Enoch P Baldwin,
Ned S Wingreen,
Justin M Kollman,
Zemer Gitai
Affiliations
Rachael M Barry
Department of Molecular Biology, Princeton University, Princeton, United States
Anne-Florence Bitbol
Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, United States
Alexander Lorestani
Department of Molecular Biology, Princeton University, Princeton, United States
Emeric J Charles
Department of Anatomy and Cell Biology, McGill University, Montreal, Canada
Chris H Habrian
Department of Molecular and Cellular Biology, University of California, Davis, Davis, United States
Jesse M Hansen
Department of Anatomy and Cell Biology, McGill University, Montreal, Canada
Hsin-Jung Li
Department of Molecular Biology, Princeton University, Princeton, United States
Enoch P Baldwin
Department of Molecular and Cellular Biology, University of California, Davis, Davis, United States
Ned S Wingreen
Department of Molecular Biology, Princeton University, Princeton, United States; Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, United States
Justin M Kollman
Department of Anatomy and Cell Biology, McGill University, Montreal, Canada; Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, Canada
Zemer Gitai
Department of Molecular Biology, Princeton University, Princeton, United States
CTP Synthetase (CtpS) is a universally conserved and essential metabolic enzyme. While many enzymes form small oligomers, CtpS forms large-scale filamentous structures of unknown function in prokaryotes and eukaryotes. By simultaneously monitoring CtpS polymerization and enzymatic activity, we show that polymerization inhibits activity, and CtpS's product, CTP, induces assembly. To understand how assembly inhibits activity, we used electron microscopy to define the structure of CtpS polymers. This structure suggests that polymerization sterically hinders a conformational change necessary for CtpS activity. Structure-guided mutagenesis and mathematical modeling further indicate that coupling activity to polymerization promotes cooperative catalytic regulation. This previously uncharacterized regulatory mechanism is important for cellular function since a mutant that disrupts CtpS polymerization disrupts E. coli growth and metabolic regulation without reducing CTP levels. We propose that regulation by large-scale polymerization enables ultrasensitive control of enzymatic activity while storing an enzyme subpopulation in a conformationally restricted form that is readily activatable.
