| dc.description.abstract | Keratin is an insoluble and protein-rich epidermal material found in e.g. feather, wool, hair. It is
produced in substantial amounts as co-product from poultry processing plants and pig slaughterhouses.
Keratin is packed by disulfide bonds and hydrogen bonds. Based on the secondary structure, keratin can
be classified into α-keratin and β-keratin. Keratinases (EC 3.4.-.- peptide hydrolases) have major potential
to degrade keratin for sustainable recycling of the protein and amino acids. Currently, the known
keratinolytic enzymes belong to at least 14 different protease families: S1, S8, S9, S10, S16, M3, M4,
M14, M16, M28, M32, M36, M38, M55 (MEROPS database). The various keratinolytic enzymes act via
endo-attack (proteases in families S1, S8, S16, M4, M16, M36), exo-attack (proteases in families S9, S10,
M14, M28, M38, M55) or by action only on oligopeptides (proteases in families M3, M32), respectively.
Other enzymes, particularly disulfide reductases, also play a key role in keratin degradation as they
catalyze the breakage of disulfide bonds for better keratinase catalysis. This review aims to contribute an
overview of keratin biomass as an enzyme substrate and a systematic analysis of currently sequenced
keratinolytic enzymes and their classification and reaction mechanisms. We also summarize and discuss
keratinase assays, available keratinase structures and finally examine the available data on uses of
keratinases in practical biorefinery protein upcycling applications | |
