Abstract
Phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) catalyzes the irreversible carboxylation of phosphoenolpyruvate (PEP) to form oxaloacetate and Pi using Mg2+ as a cofactor. The three-dimensional structures of PEPC from Escherichia coli and Zea mays were elucidated by X-ray crystallographic analysis. Together with the data of site-directed mutagenesis, the catalytic site was located at the C-terminal side of β8-barrel structure and the binding sites for allosteric inhibitor (C4-dicarboxylic acid) was assigned. Furthermore, putative binding site for an activator (glucose 6-phosphate) was also disclosed. By comparison among the enzyme structures liganded either with an allosteric inhibitor, metal cofactor, PEP analogue or sulfate anion, the role of flexible loops in catalytic and regulatory functions was elucidated and the allosteric regulation mechanism was deduced.
