Crystal structure of a family 6 cellobiohydrolase from the basidiomycete Phanerochaete chrysosporium

Cellobiohydrolases belonging to glycoside hydrolase family 6 (CBH II, Cel6A) play key roles in the hydrolysis of crystalline cellulose. CBH II from the white-rot fungus Phanerochaete chrysosporium (PcCel6A) consists of a catalytic domain (CD) and a carbohydrate-binding module connected by a linker peptide, like other known fungal cellobiohydrolases. In the present study, the CD of PcCel6A was crystallized without ligands, and p-nitrophenyl β-d-cellotrioside (pNPG3) was soaked into the crystals. The determined structures of the ligand-free and pNPG3-soaked crystals revealed that binding of cellobiose at substrate subsites +1 and +2 induces a conformational change of the N-terminal and C-terminal loops, switching the tunnel-shaped active site from the open to the closed form.