Abstract
The initial steps of photosynthetic carbon reduction and photorespiratory carbon oxidation cycles are catalyzed by the key enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) by combining CO2 and O2, respectively, to ribulose-1,5-bisphosphate. Since Rubisco limits photosynthesis and thus plant growth, an understanding of the structure/function relationships of this enzyme is extremely important to design Rubisco superior in catalysis and to improve crop productivity. Rubisco from an acido-thermophilic unicellular red alga, Galdieria partita (optimal growth conditions are pH 2 and 40 °C) has the highest specificity for carboxylation reaction among the Rubiscos reported so far. In order to clarify the structural basis of the excellent property of the Galdieria enzyme, X-ray crystallography of this enzyme has been conducted. In this symposium, we show crystal structures of Galdieria Rubisco complexed with some different ligands, and propose the mechanism in which the enzyme acquired the high functionality.
