Quantum Mechanical Study of Oxygen Ligands Protonation for the Stable States of the Laccase Active Site

Laccases are enzymes catalyzing the oxidation of a wide range of organic and inorganic substrates accompanied by molecular oxygen reduction to water. Recently, oxygen reduction by laccases has been studied by single-crystal serial X-ray crystallography with increasing absorption doses at subatomic resolution. There were two determined structures corresponding to the reduced and oxidized stable states of the laccase active site. However, the protonation of the oxygen ligands involved cannot be determined even at subatomic resolution. In the present work, the protonation of oxygen ligands in the active site of laccase for the two stable states determined in the X-ray study was explored using quantum mechanical and continuum-electrostatics calculations. This is important for understanding the reaction of the oxygen reduction mechanism in laccases. The high precision of X-ray data at subatomic resolutions allowed us to optimize the quantum mechanical calculations.

Automated summary

Laccases are enzymes that oxidize various organic and inorganic substrates while reducing molecular oxygen to water. Recent studies using single-crystal serial X-ray crystallography have determined the structures of the reduced and oxidized states of the laccase active site. However, the protonation of the oxygen ligands involved cannot be determined even at subatomic resolution. This study used quantum mechanical and continuum-electrostatics calculations to explore the protonation of oxygen ligands in the active site of laccase. The high precision of X-ray data at subatomic resolutions allowed for optimized quantum mechanical calculations.