The importance of the strictly conserved, C-terminal glycine residue in phosphoenolpyruvate carboxylase for overall catalysis: mutagenesis and truncation of GLY-961 in the sorghum C4 leaf isoform.
Abstract
Phosphoenolpyruvate carboxylase (PEPC) is a "multifaceted," allosteric enzyme involved in C4 acid metabolism in green plants/microalgae and prokaryotes. Before the elucidation of the three-dimensional structures of maize C4 leaf and Escherichia coli PEPC, our truncation analysis of the sorghum C4 homologue revealed important roles for the enzyme's C-terminal alpha-helix and its appended QNTG961 tetrapeptide in polypeptide stability and overall catalysis, respectively. Collectively, these functional and structural observations implicate the importance of the PEPC C-terminal tetrapeptide for both catalysis and negative allosteric regulation. We have now more finely dissected this element of PEPC structure-function by modification of the absolutely conserved C-terminal glycine of the sorghum C4 isoform by site-specific mutagenesis (G961(A/V/D)) and truncation (DeltaC1/C4). Although the C4 polypeptide failed to accumulate in a PEPC- strain (XH11) of E. coli transformed with the Asp mutant, the other variants were produced at wild-type levels. Although neither of these four mutants displayed an apparent destabilization of the purified PEPC homotetramer, all were compromised catalytically in vivo and in vitro. Functional complementat...Continue Reading
References
Citations
Related Concepts
Related Feeds
ASBMB Publications
The American Society for Biochemistry and Molecular Biology (ASBMB) includes the Journal of Biological Chemistry, Molecular & Cellular Proteomics, and the Journal of Lipid Research. Discover the latest research from ASBMB here.