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

Cellobiose dehydrogenase (CDH) participates in the degradation of cellulose and lignin. The protein is an extracellular flavocytochrome with a b-type cytochrome domain (CYTcdh) connected to a flavodehydrogenase domain (DHcdh). DHcdh 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 DHcdh to an acceptor, either directly or via CYTcdh. Here, we decribe the crystal structure of Phanerochaete chrysosporium DHcdh determined at 1.5 Angstrom resolution. DHcdh 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 DHcdh 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 alpha/beta type and a substrate-binding subdomain consisting of a seven-stranded beta sheet and six helices. Docking of CYTcdh, and DHcdh suggests that CYTcdh covers the active-site entrance in DHcdh, 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 DHcdh, we propose that the enzyme discriminates against glucose by favouring interaction with the non-reducing end of cellobiose. (C) 2002 Academic Press.