title: Greater efficiency of photosynthetic carbon fixation due to single amino-acid substitution.
abstract: The C4-photosynthetic carbon cycle is an elaborated addition to the classical C3-photosynthetic pathway, which improves solar conversion efficiency. The key enzyme in this pathway, phosphoenolpyruvate carboxylase, has evolved from an ancestral non-photosynthetic C3 phosphoenolpyruvate carboxylase. During evolution, C4 phosphoenolpyruvate carboxylase has increased its kinetic efficiency and reduced its sensitivity towards the feedback inhibitors malate and aspartate. An open question is the molecular basis of the shift in inhibitor tolerance. Here we show that a single-point mutation is sufficient to account for the drastic differences between the inhibitor tolerances of C3 and C4 phosphoenolpyruvate carboxylases. We solved high-resolution X-ray crystal structures of a C3 phosphoenolpyruvate carboxylase and a closely related C4 phosphoenolpyruvate carboxylase. The comparison of both structures revealed that Arg884 supports tight inhibitor binding in the C3-type enzyme. In the C4 phosphoenolpyruvate carboxylase isoform, this arginine is replaced by glycine. The substitution reduces inhibitor affinity and enables the enzyme to participate in the C4 photosynthesis pathway.
authors: Cluster of Excellence on Plant Sciences (CEPLAS), Institute of Biochemical Plant Physiology, Heinrich Heine University, Universitaetsstr. 1, 40225 Düsseldorf, Germany.
authors: Judith Katharina
authors: JK
authors: Paulus
authors: Daniel
authors: D
authors: Schlieper
authors: Georg
authors: G
authors: Groth
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000494:pharmacology; D025461:Feedback, Physiological / Q000187:drug effects; D037142:Flaveria / Q000187:drug effects / Q000201:enzymology*; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000187:drug effects / Q000235:genetics; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010730:Phosphoenolpyruvate Carboxylase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010788:Photosynthesis / Q000187:drug effects; D055672:Static Electricity; D013379:Substrate Specificity / Q000187:drug effects; D003313:Zea mays / Q000201:enzymology
chemical_list: D004791:Enzyme Inhibitors; D050505:Mutant Proteins; D010730:Phosphoenolpyruvate Carboxylase