4CSC

STRUCTURE OF TERNARY COMPLEXES OF CITRATE SYNTHASE WITH D-AND L-MALATE: MECHANISTIC IMPLICATIONS

Summary for 4CSC

• Entry DOI: 10.2210/pdb4csc/pdb
• Descriptor: CITRATE SYNTHASE, D-MALATE, ACETYL COENZYME *A, ... (4 entities in total)
• Functional Keywords: oxo-acid-lyase
• Biological source: Gallus gallus (chicken)
• Cellular location: Mitochondrion matrix: P23007
• Total number of polymer chains: 1
• Total formula weight: 48265.83

Authors

Karpusas, M.,Holland, D.,Remington, S.J. (deposition date: 1990-05-07, release date: 1991-04-15, Last modification date: 2024-02-28)

Primary citation

Karpusas, M.,Holland, D.,Remington, S.J.
1.9-A structures of ternary complexes of citrate synthase with D- and L-malate: mechanistic implications.
Biochemistry, 30:6024-6031, 1991

PubMed Abstract: The structures of four isomorphous crystals of ternary complexes of chicken heart citrate synthase with D- or L-malate and acetyl coenzyme A or carboxymethyl coenzyme A have been determined by X-ray crystallography and fully refined at 1.9-A resolution. The structures show that both L-malate and D-malate bind in a very similar way in the presence of acetylCoA and that the enzyme conformation is "closed". Hydrogen bond geometry is suggested to account for the difference in binding constants of the two stereoisomers. The structures suggest that steric hindrance can account for the observation that proton exchange of acetyl coenzyme A with solvent is catalyzed by citrate synthase in the presence of L-malate but not D-malate. The ternary complexes with malate reveal the mode of binding of the substrate acetylCoA in the ground state. The carbonyl oxygen of the acetyl group is hydrogen bonded to a water molecule and to histidine 274, allowing unambiguous identification of the orientation of this group. The structures support the hypothesis that carboxymethyl coenzyme A is a transition-state analogue for the enolization step of the reaction (Bayer et al., 1981) and additionally support proposed mechanisms for the condensation reaction (Karpusas et al., 1990; Alter et al., 1990).

PubMed: 2043640
DOI: 10.1021/bi00238a028

Experimental method

X-RAY DIFFRACTION (1.9 Å)