Cellobiose Dehydrogenase – A Flavocytochrome from Wood-Degrading, Phytopathogenic and Saprotropic Fungi

Abstract

Cellobiose dehydrogenase, the only currently known extracellular flavocytochrome, is formed not only by a number of wood-degrading but also by various phytopathogenic fungi. This inducible enzyme participates in early events of lignocellulose degradation, as investigated in several basidiomycete fungi at the transcriptional and translational level. However, its role in the ascomycete fungi is not yet obvious. Comprehensive sequence analysis of CDH-encoding genes and their translational products reveals significant sequence similarities along the entire sequences and also a common domain architecture. All known cellobiose dehydrogenases fall into two related subgroups. Class-I members are represented by sequences from basidiomycetes whereas class-II comprises longer, more complex sequences from ascomycete fungi. Cellobiose dehydrogenase is typically a monomeric protein consisting of two domains joined by a protease-sensitive linker region. Each larger (dehydrogenase) domain is flavin-associated while the smaller (cytochrome) domains are haem-binding. The latter shorter domains are unique sequence motifs for all currently known flavocytochromes. Each cytochrome domain of CDH can bind a single haem b as prosthetic group. The larger dehydrogenase domain belongs to the glucose-methanol-choline (GMC) oxidoreductase superfamily - a widespread flavoprotein evolutionary line. The larger domains can be further divided into a flavin-binding subdomain and a substrate-binding subdomain. In addition, the class-II (but not class-I) proteins can possess a short cellulose-binding module of type 1 at their C-termini. All the cellobiose dehydrogenases oxidise cellobiose, cellodextrins, and lactose to the corresponding lactones using a wide spectrum of different electron acceptors. Their flexible specificity serves as a base for the development of possible biotechnological applications.

Production of oligosaccharides and cellobionic acid by Fibrobacter succinogenes S85 growing on sugars, cellulose and wheat straw

“…The presence of cellobionic acid is very surprising. It is usually produced in aerobic lignocellulolytic fungi through the activity of a cellobiose dehydrogenase (CDH) that converts cellobiose into cellobionolactone, an unstable compound rapidly spontaneously hydrolysed into cellobionic acid (Higham et al 1994;Zamocky et al 2006). CDH activity was also found in cellulolytic bacteria (Li et al 1996).…”

A Direct Electron Transfer‐Based Glucose/Oxygen Biofuel Cell Operating in Human Serum

“…The catalytic domain contains one flavin adenine dinucleotide (FAD) and the heme domain contains one heme b as cofactors (Figure 1, right part). CDH oxidises cellodextrins and lactose at the FAD domain and may, depending on its origin, also oxidise monosaccharides such as glucose [16]. The reduced FAD domain can be reoxidised directly by various electron acceptors or the electrons can be sequentially transferred to the heme domain, which in turn donates the electrons directly to the electrode acting like a 1 e -acceptor [17].…”

Bioethanol: Feedstock Alternatives, Pretreatments, Lignin Chemistry, and the Potential for Green Value-Added Lignin Co-Products

“…Cellobiose dehydrogenases are enzymes that oxidize cellobiose [116]. Unlike other cellulases, which act via hydrolysis, cellobiose dehydrogenases produce H 2 O 2 and oxidize cellobiose to reduce Fe 3+ to Fe 2+ or Cu 2+ to Cu + [33].…”