Reconstituted IMPDH polymers accommodate both catalytically active and inactive conformations
| Autor: | Jeffrey R. Peterson, Peter Michener, Anika L. Burrell, Andrew J. Andrews, Sajitha Anthony, Jacqueline C. Simonet, Justin M. Kollman, Matthew C. Johnson, Yin-Ming Kuo, Krisna C. Duong-Ly |
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| Rok vydání: | 2017 |
| Předmět: |
0301 basic medicine
chemistry.chemical_classification GTP' Guanine Allosteric regulation fungi Substrate (chemistry) food and beverages macromolecular substances Cell Biology Biology 03 medical and health sciences chemistry.chemical_compound 030104 developmental biology chemistry Polymerization Biophysics Nucleotide Brief Reports Histone octamer Molecular Biology Macromolecule |
| Zdroj: | Molecular Biology of the Cell |
| ISSN: | 1939-4586 |
| Popis: | The metabolic enzyme IMPDH assembles into octamers that can polymerize and form micron-scale structures in cells. Octamers can adopt active, expanded or inactive, compressed conformations driven by allosteric nucleotide and substrate binding. Both forms are accommodated within polymers, and polymerization alone does not alter catalytic activity. Several metabolic enzymes undergo reversible polymerization into macromolecular assemblies. The function of these assemblies is often unclear, but in some cases they regulate enzyme activity and metabolic homeostasis. The guanine nucleotide biosynthetic enzyme inosine monophosphate dehydrogenase (IMPDH) forms octamers that polymerize into helical chains. In mammalian cells, IMPDH filaments can associate into micron-length assemblies. Polymerization and enzyme activity are regulated in part by binding of purine nucleotides to an allosteric regulatory domain. ATP promotes octamer polymerization, whereas guanosine triphosphate (GTP) promotes a compact, inactive conformation whose ability to polymerize is unknown. Also unclear is whether polymerization directly alters IMPDH catalytic activity. To address this, we identified point mutants of human IMPDH2 that either prevent or promote polymerization. Unexpectedly, we found that polymerized and nonassembled forms of recombinant IMPDH have comparable catalytic activity, substrate affinity, and GTP sensitivity and validated this finding in cells. Electron microscopy revealed that substrates and allosteric nucleotides shift the equilibrium between active and inactive conformations in both the octamer and the filament. Unlike other metabolic filaments, which selectively stabilize active or inactive conformations, recombinant IMPDH filaments accommodate multiple states. These conformational states are finely tuned by substrate availability and purine balance, while polymerization may allow cooperative transitions between states. |
| Databáze: | OpenAIRE |
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