Site-directed mutagenesis of Flaveria trinervia phosphoenolpyruvate carboxylase: Arg450 and Arg767 are essential for catalytic activity and Lys829 affects substrate binding.

Phosphoenolpyruvate carboxylases (PEPC) of all known sequences contain 11 conserved arginine and two lysine residues located in highly conservative regions. Previous chemical modifications show that arginine and lysine residues are essential for catalytic activity. Three conserved residues, Arg450, Arg767 and Lys829, in PEPC of Flaveria trinervia were converted to glycine. All three mutant PEPC proteins were similarly expressed in Escherichia coli. However, mutant Gly450 and Gly767 PEPCs had no catalytic activity and Gly829 PEPC showed increased Km for PEP and Mg2+. It seems that Arg450 and Arg767 are essential for PEPC function while Lys829 might be associated with PEP and/or Mg2+ binding domain.