Structural basis for cellobiose dehydrogenase action during oxidative cellulose degradation

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Fungal cellulose depolymerization utilizes an oxidative mechanism involving cellobiose dehydrogenases (CDH) and lytic polysaccharide monooxygenases (LPMO).
• Mechanistic studies of CDH have been limited by a lack of structural information.
• CDH comprises a haem-binding cytochrome (CYT) linked to a flavin-dependent dehydrogenase (DH), facilitating electron transfer from cellobiose to LPMO.

Purpose of the Study:

• To elucidate the structural basis of electron transfer within CDH.
• To understand the conformational dynamics governing interdomain electron transfer (IET) between redox centers.
• To provide structural insights into CDH function in cellulose depolymerization.

Main Methods:

• Comprehensive structural analyses of CDH conformers.
• Structure-based site-directed mutagenesis.
• Rapid kinetics analysis and molecular docking.

Main Results:

• Structural analyses revealed CDH conformers that dictate electron transfer between redox centers.
• Flavin-to-haem IET is facilitated by a haem propionate group.
• Rapid IET necessitates a closed CDH state where the propionate is enclosed by the DH domain.
• Reduced haem in CYT enables LPMO reduction, initiating oxygen activation and cellulose depolymerization.

Conclusions:

• The study provides a detailed structural mechanism for electron transfer in CDH.
• Understanding CDH structure-function relationships is crucial for optimizing fungal cellulose degradation.
• These findings advance the mechanistic understanding of oxidative cellulose depolymerization by fungi.