A metagenomic ‘dark matter’ enzyme catalyses oxidative cellulose conversion

The breakdown of cellulose is one of the most important reactions in nature1,2 and is central to biomass conversion to fuels and chemicals3. However, the microfibrillar organization of cellulose and its complex interactions with other components of the plant cell wall poses a major challenge for enzymatic conversion4. Here, by mining the metagenomic ‘dark matter’ (unclassified DNA with unknown function) of a microbial community specialized in lignocellulose degradation, we discovered a metalloenzyme that oxidatively cleaves cellulose. This metalloenzyme acts on cellulose through an exo-type mechanism with C1 regioselectivity, resulting exclusively in cellobionic acid as a product. The crystal structure reveals…