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Substrate induced conformational changes in argininosuccinate synthetase.
Christopher T Lemke1, P Lynne Howell
1Structural Biology and Biochemistry, Research Institute, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, M5G 1X8, Canada.
The Journal of Biological Chemistry
|January 26, 2002
Summary
Structural insights into argininosuccinate synthetase (AS) reveal enzyme mechanisms. Understanding AS, crucial for urea and arginine-citrulline cycles, aids research into citrullinemia and septic shock.
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Argininosuccinate synthetase (AS) is a key enzyme in the urea and arginine-citrulline cycles.
- AS deficiency causes citrullinemia, a severe urea cycle disorder.
- AS overexpression is linked to hypotension in septic shock via nitric oxide production.
Purpose of the Study:
- To determine the crystal structures of Escherichia coli argininosuccinate synthetase (EAS) in complex with ATP and citrulline.
- To elucidate the interactions between EAS, ATP, and citrulline at atomic resolution.
- To provide structural basis for understanding AS enzymatic mechanism and kinetics.
Main Methods:
- X-ray crystallography
- Determination of crystal structures at 2.0-A resolution
- Structural comparisons with apoenzyme and other complexes
Main Results:
- First structures of EAS with a nucleotide substrate (ATP) determined.
- Identified key residues interacting with ATP and citrulline.
- Revealed two distinct, catalytically relevant ATP conformations.
- Observed ATP-induced conformational changes in the nucleotide binding domain.
Conclusions:
- The determined structures provide detailed insights into argininosuccinate synthetase catalysis.
- Structural data explains observed enzyme kinetics and mechanism.
- These findings advance the understanding of urea cycle disorders and septic shock mechanisms.