PMID:9927652
| Citation |
Kai, Y, Matsumura, H, Inoue, T, Terada, K, Nagara, Y, Yoshinaga, T, Kihara, A, Tsumura, K and Izui, K (1999) Three-dimensional structure of phosphoenolpyruvate carboxylase: a proposed mechanism for allosteric inhibition. Proc. Natl. Acad. Sci. U.S.A. 96:823-8 |
|---|---|
| Abstract |
The crystal structure of phosphoenolpyruvate carboxylase (PEPC; EC 4. 1.1.31) has been determined by x-ray diffraction methods at 2.8-A resolution by using Escherichia coli PEPC complexed with L-aspartate, an allosteric inhibitor of all known PEPCs. The four subunits are arranged in a "dimer-of-dimers" form with respect to subunit contact, resulting in an overall square arrangement. The contents of alpha-helices and beta-strands are 65% and 5%, respectively. All of the eight beta-strands, which are widely dispersed in the primary structure, participate in the formation of a single beta-barrel. Replacement of a conserved Arg residue (Arg-438) in this linkage with Cys increased the tendency of the enzyme to dissociate into dimers. The location of the catalytic site is likely to be near the C-terminal side of the beta-barrel. The binding site for L-aspartate is located about 20 A away from the catalytic site, and four residues (Lys-773, Arg-832, Arg-587, and Asn-881) are involved in effector binding. The participation of Arg-587 is unexpected, because it is known to be catalytically essential. Because this residue is in a highly conserved glycine-rich loop, which is characteristic of PEPC, L-aspartate seemingly causes inhibition by removing this glycine-rich loop from the catalytic site. There is another mobile loop from Lys-702 to Gly-708 that is missing in the crystal structure. The importance of this loop in catalytic activity was also shown. Thus, the crystal-structure determination of PEPC revealed two mobile loops bearing the enzymatic functions and accompanying allosteric inhibition by L-aspartate. |
| Links | |
| Keywords |
Allosteric Regulation; Amino Acid Sequence; Amino Acid Substitution; Arginine; Aspartic Acid/chemistry; Aspartic Acid/pharmacology; Computer Simulation; Conserved Sequence; Crystallography, X-Ray; Cysteine; Dimerization; Escherichia coli/enzymology; Models, Molecular; Molecular Sequence Data; Phosphoenolpyruvate Carboxylase/antagonists & inhibitors; Phosphoenolpyruvate Carboxylase/chemistry; Phosphoenolpyruvate Carboxylase/metabolism; Protein Structure, Secondary; Sequence Alignment; Sequence Homology, Amino Acid; Zea mays/enzymology |
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