Targeting the reactive intermediate in polysaccharide monooxygenases.

Area of Science:

• Biochemistry
• Biofuel production
• Enzymology

Background:

• Lytic polysaccharide monooxygenases (LPMOs) are copper enzymes crucial for cellulose depolymerization.
• Their oxidative mechanism is vital for biofuel production, but the active intermediate remains unidentified.
• The bond-dissociation energy (BDE) is a common metric for bond-activation potential in model systems.

Purpose of the Study:

• To elucidate the nature of the reactive intermediate in LPMO-catalyzed C-H bond activation.
• To bridge the gap between inorganic model complexes and the LPMO active site using computational methods.
• To determine the sequence of bond-breaking and activation steps in LPMO reactions.

Main Methods:

• Quantum-chemical cluster calculations were employed.
• The homolytic bond-dissociation energy (BDE) was calculated for potential LPMO intermediates.
• Calculations focused on bridging the gap between model complexes and the LPMO active site.

Main Results:

• Calculated BDEs suggest specific reactive intermediates.
• The potential intermediates identified are Cu(II)-oxyl, Cu(III)-oxyl, or Cu(III)-hydroxide.
• These findings indicate that O-O bond breaking occurs prior to C-H bond activation.

Conclusions:

• The study identifies potential reactive intermediates in LPMO catalysis.
• The results clarify the mechanistic steps, specifically the timing of O-O bond cleavage relative to C-H activation.
• This provides crucial insights into LPMO function for biofuel applications.