A metagenomic 'dark matter' enzyme catalyses oxidative cellulose conversion

Area of Science:

• Biochemistry
• Microbiology
• Biotechnology

Background:

• Cellulose breakdown is crucial for biomass conversion but is challenging due to cellulose's complex structure.
• Microbial communities specialized in lignocellulose degradation harbor enzymes with potential biotechnological applications.

Purpose of the Study:

• To discover novel enzymes involved in cellulose degradation from unclassified microbial DNA.
• To characterize the structure, mechanism, and biotechnological potential of a newly identified cellulose-cleaving metalloenzyme.

Main Methods:

• Metagenomic mining of microbial communities for novel enzymes.
• Biochemical assays to determine enzyme activity and product specificity (C1 regioselectivity, cellobionic acid production).
• X-ray crystallography to elucidate enzyme structure.
• Engineering of Trichoderma reesei to express the metalloenzyme and assess its performance on lignocellulosic biomass.

Main Results:

• Discovery of a novel metalloenzyme that oxidatively cleaves cellulose via an exo-type mechanism with C1 regioselectivity.
• Structural analysis revealed a copper-containing enzyme with a unique cellulose binding site and a homodimeric configuration.
• Engineered Trichoderma reesei expressing the enzyme enhanced glucose release from pretreated lignocellulosic biomass.

Conclusions:

• The discovered metalloenzyme represents a new class of redox enzymes for biomass recalcitrance.
• This enzyme has significant biotechnological potential for converting agro-industrial residues into value-added bioproducts.
• The findings contribute to a sustainable bio-based economy by improving biomass conversion efficiency.