Fungal chitinases: diversity, mechanistic properties and biotechnological potential

Abstract

Chitin derivatives, chitosan and substituted chito-oligosaccharides have a wide spectrum of applications ranging from medicine to cosmetics and dietary supplements. With advancing knowledge about the substrate-binding properties of chitinases, enzyme-based production of these biotechnologically relevant sugars from biological resources is becoming increasingly interesting. Fungi have high numbers of glycoside hydrolase family 18 chitinases with different substrate-binding site architectures. As presented in this review, the large diversity of fungal chitinases is an interesting starting point for protein engineering. In this review, recent data about the architecture of the substrate-binding clefts of fungal chitinases, in connection with their hydrolytic and transglycolytic abilities, and the development of chitinase inhibitors are summarized. Furthermore, the biological functions of chitinases, chitin and chitosan utilization by fungi, and the effects of these aspects on biotechnological applications, including protein overexpression and autolysis during industrial processes, are discussed in this review.

Fig. 1

Schematic representation of the substrate-binding clefts of GH family 18 chitinases. a Chitinases have multiple sugar-binding sites in their long substrate-binding clefts. Cleavage occurs between the +1 and −1 sugar. In these two subsites, the substrate has contact with two amino acids (D and E) that are part of the diagnostic catalytic DXXDXDE motif, which is essential for catalytic cleave by GH family 18 chitinases. b Sg A (class V) and C chitinases have narrow and tunnel-shaped substrate-binding clefts, and sg B (class III) chitinases have wide and open substrate-binding clefts

Fig. 2

Chemical structures of chitinase inhibitors. a Allosamidin. b Argadin. c Argifin. d  C2-dicaffeine

Fig. 3

Effect of a chitinolytic enzyme mix from the autolytic phase of T. atroviride cultures on germination of different fungi. a T. atroviride. b T. reesei. c Neurospora crassa. d A. niger. Spores were incubated in potato dextrose broth and at 28° for 15 h (Ta, Tr, An) or 8 h (Nc). In 20-mM Tris–HCl (pH 8.0) buffer or buffer alone (control), 33% of the medium were replaced with T. atroviride enzymes. Scale bars = 20 μm