FUNCTION-DEPENDENT CONFIGURATIONAL CHANGES OF BACTERIAL RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE

The key carboxylating enzyme of the reductive pentose phosphate cycle D-Ribulose-1,5-bisphosphate carboxylase/oxygenase [RuBisCO] isolated from the chemolithoautotrophic, H2-oxidizing bacterium Alcaligenes eutrophus H16 exists in three stable functional states: As the active enzyme [Ea] (in the presence of Mg2+ and HCO3-); as inactivated enzyme [Eia] (in the absence of Mg2+ and HCO3-) and as the enzyme locked in an in vitro transition state [CABP-E] (Ea fully saturated with the transition state analogue 2-carboxy-D-arabinitol-1,5-bisphosphate [CABP]). Three different functional state-correlated configurations of the enzyme were revealed by electron microscopy of 2D crystals and single molecules, and by X-ray crystallography of 3D crystals of the CABP-E.