21st Century Guidebook to Fungi, SECOND EDITION, by David Moore, Geoffrey D. Robson and Anthony P. J. Trinci

Table of Contents

1. Chapter 9: Continuing the diversity theme: cell and tissue differentiation
2. Chapter 10: Fungi in ecosystems
   1. Contributions of fungi to ecosystems
   2. Breakdown of polysaccharide: cellulose
   3. Breakdown of polysaccharide: hemicellulose
   4. Breakdown of polysaccharide: pectins
   5. Breakdown of polysaccharide: chitin
   6. Breakdown of polysaccharide: starch and glycogen
   7. Lignin degradation
   8. Digestion of protein
   9. Lipases and esterases
   10. Phosphatases and sulfatases
   11. The flow of nutrients: transport and translocation
   12. Primary (intermediary) metabolism
   13. Secondary metabolism
   14. Chapter 10 References and further reading
   15. Buy a PDF of Chapter 10
3. Chapter 11: Exploiting fungi for food

10.5 Breakdown of polysaccharide: chitin

Chitin, in which the repeating unit is the same as that in cellulose except that the hydroxyl group at C-2 is replaced by an acetamido group (Fig. 2), is the second most abundant polymer on Earth as it occurs in the exoskeletons of arthropods and, of course, in fungal cell walls. Polysaccharides which contain amino sugars or their derivatives are called mucopolysaccharides. Chitin is degraded by chitinase, a glucan hydrolase which attacks the β1→4 glycosidic bonds, eventually producing the disaccharide chitobiose which is then converted to the monosaccharide N-acetylglucosamine by chitobiase (Seidl, 2008). Chitinase may also be involved in fungal wall synthesis (see Chapter 6). Several chitinases, which are glycoside hydrolase family enzymes, are produced by fungi and can have different substrate-binding site structures and are obviously specialised for different functions (Zhou et al., 2019). Derivatives of chitin and chitosan have found many commercial uses from medicine to cosmetics and dietary supplements, so fungal chitinases have biotechnological applications, also (Seidl, 2008; Hartl et al., 2012).

Fig. 2. Structural formulae of chitin and its constituents. Chitin structure is similar to that of cellulose (Fig. 10.1), except that acetylamino groups (CH3CONH-) replace the hydroxyl groups at carbon position 2 of the glucose molecule. Approximately 16% of naturally occurring chitin units are deacetylated. Modified from Moore, 1998.

Updated February, 2020