title: Large-scale filament formation inhibits the activity of CTP synthetase.
abstract: 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.
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, United States.
authors.forename: Rachael M
authors.initials: RM
authors.lastname: Barry
authors.affiliation: Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, United States.
authors.forename: Anne-Florence
authors.initials: AF
authors.lastname: Bitbol
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, United States.
authors.forename: Alexander
authors.initials: A
authors.lastname: Lorestani
authors.affiliation: Department of Anatomy and Cell Biology, McGill University, Montreal, Canada.
authors.forename: Emeric J
authors.initials: EJ
authors.lastname: Charles
authors.affiliation: Department of Molecular and Cellular Biology, University of California, Davis, Davis, United States.
authors.forename: Chris H
authors.initials: CH
authors.lastname: Habrian
authors.affiliation: Department of Anatomy and Cell Biology, McGill University, Montreal, Canada.
authors.forename: Jesse M
authors.initials: JM
authors.lastname: Hansen
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, United States.
authors.forename: Hsin-Jung
authors.initials: HJ
authors.lastname: Li
authors.affiliation: Department of Molecular and Cellular Biology, University of California, Davis, Davis, United States.
authors.forename: Enoch P
authors.initials: EP
authors.lastname: Baldwin
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, United States Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, United States.
authors.forename: Ned S
authors.initials: NS
authors.lastname: Wingreen
authors.affiliation: Department of Anatomy and Cell Biology, McGill University, Montreal, Canada Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, Canada.
authors.forename: Justin M
authors.initials: JM
authors.lastname: Kollman
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, United States zgitai@princeton.edu.
authors.forename: Zemer
authors.initials: Z
authors.lastname: Gitai
mesh_terms: D019731:Carbon-Nitrogen Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003570:Cytidine Triphosphate / Q000096:biosynthesis*; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D055503:Protein Multimerization; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D011993:Recombinant Fusion Proteins; D003570:Cytidine Triphosphate; D019731:Carbon-Nitrogen Ligases; C019951:CTP synthetase
keywords: CTP synthetase; enzyme regulation; nucelotide metabolism; pyrimidine metabolism