Multiscale Modelling of Lytic Polysaccharide Monooxygenases

Area of Science:

• Biochemistry
• Computational Chemistry
• Enzymology

Background:

• Lytic polysaccharide monooxygenases (LPMOs) are copper-metalloenzymes that enhance polysaccharide degradation.
• LPMOs are of significant interest for biofuel production from cellulose.
• The mechanism of dioxygen activation by LPMO copper active sites remains incompletely understood.

Purpose of the Study:

• To investigate the initial steps of the LPMO catalytic mechanism using hybrid quantum mechanics/molecular mechanics (QM/MM) methods.
• To elucidate the reduction of Cu(II) to Cu(I) and the formation of a Cu(II)-superoxide complex.
• To compare computational findings with existing experimental data and previous theoretical models.

Main Methods:

• Employed hybrid QM/MM methods to model the LPMO active site and its protein environment.
• Investigated the reduction of the copper active site from Cu(II) to Cu(I).
• Analyzed the formation and stability of Cu(II)-superoxide complexes, considering both equatorial and axial binding modes.

Main Results:

• Obtained novel structural insights into the LPMO mechanism, differing from previous small QM-cluster calculations.
• Identified the equatorial isomer of the Cu(II)-superoxide complex as significantly more stable (>60 kJ/mol) than the axial isomer.
• Revealed stabilization of the equatorial isomer through interactions with a second-coordination-sphere glutamine residue.

Conclusions:

• The study provides a more accurate computational model for LPMO active site mechanisms.
• The findings suggest a crucial role for a second-coordination-sphere glutamine in stabilizing the superoxide complex.
• The computationally predicted coordination mode aligns with recent experimental observations, advancing understanding of LPMO function.