Crystal structure of the flavoprotein domain of the extracellular flavocytochrome cellobiose dehydrogenase

Abstract

Cellobiose dehydrogenase (CDH) participates in the degradation of cellulose and lignin. The protein is an extracellular flavocytochrome with a b-type cytochrome domain (CYT cdh ) connected to a flavodehydrogenase domain (DH cdh ). DH cdh catalyses a two-electron oxidation at the anomeric C1 position of cellobiose to yield cellobiono-1,5-lactone, and the electrons are subsequently transferred from DH cdh to an acceptor, either directly or via CYT cdh . Here, we decribe the crystal structure of Phanerochaete chrysosporium DH cdh determined at 1.5 Å resolution. DH cdh belongs to the GMC family of oxidoreductases, which includes glucose oxidase (GOX) and cholesterol oxidase (COX); however, the sequence identity with members of the family is low. The overall fold of DH cdh is p-hydroxybenzoate hydroxylase-like and is similar to, but also different from, that of GOX and COX. It is partitioned into an FAD-binding subdomain of α/β type and a substrate-binding subdomain consisting of a seven-stranded β sheet and six helices. Docking of CYT cdh and DH cdh suggests that CYT cdh covers the active-site entrance in DH cdh , and that the resulting distance between the cofactors is within acceptable limits for inter-domain electron transfer. Based on docking of the substrate, cellobiose, in the active site of DH cdh , we propose that the enzyme discriminates against glucose by favouring interaction with the non-reducing end of cellobiose.