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Structural basis for ordered substrate binding and cooperativity in aspartate transcarbamoylase
Jie Wang1, Kimberly A Stieglitz, James P Cardia
1Department of Chemistry, Boston College, Merkert Chemistry Center, Chestnut Hill, MA 02467, USA.
Summary
Aspartate transcarbamoylase undergoes key structural changes upon substrate binding. These conformational shifts, revealed by X-ray crystallography, explain enzyme function and cooperativity.
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Aspartate transcarbamoylase (ATCase) is a crucial enzyme in pyrimidine biosynthesis.
- Understanding ATCase's mechanism is vital for metabolic pathway regulation.
Purpose of the Study:
- To elucidate the structural basis of ATCase function and substrate-induced conformational changes.
- To provide atomic-level insights into the ordered substrate binding and cooperativity of ATCase.
Main Methods:
- X-ray crystallography was employed to determine ATCase structures.
- In silico docking experiments were performed to complement structural data.
Main Results:
- Structures of ATCase were obtained in the absence and presence of carbamoyl phosphate.
- Carbamoyl phosphate binding induces a conformational change, altering active site electrostatics and creating an aspartate binding pocket.
- Aspartate binding triggers a second conformational change, domain closure, facilitating catalysis and cooperativity.
Conclusions:
- The study reveals a two-step induced-fit mechanism for ATCase activation.
- Structural data explains ordered substrate binding and the origin of homotropic cooperativity in ATCase.
- These findings offer a detailed molecular understanding of a key metabolic enzyme.