Mechanistic Insights into Keratin Degradation by Onygena corvina

Keratin-rich byproducts from the poultry, textile, and leather industries pose a significant challenge for sustainable waste management due to their highly recalcitrant nature. While microbial degradation may offer a viable solution, the mechanisms underlying keratin breakdown remain largely unexplored. In this study, we employed a high-resolution proteogenomic approach to characterize the keratinolytic machinery of Onygena corvina, a non-pathogenic saprophytic fungus. Using a membrane agar plate method with insoluble substrates, we obtained secretomes enriched in secreted and substrate-bound proteins during growth on - and {beta}-keratin-rich substrates, specifically wool and feather meal. Our findings reveal that O. corvina has a richer proteolytic machinery than previously reported, including enzymes that are used across keratin types, as well as enzymes that are specifically targeted to either - or {beta}-keratin. In addition to proteases, the secretomes contain numerous other proteins, including cell wall-modifying enzymes, oxidoreductases, esterases, phosphatases, and sialidases that are involved in the deconstruction of keratin. We propose that these additional enzymes destabilize keratin through a combination of mechanical keratinolysis, removal of post-translational modifications, reduction of disulfide bonds, and cleavage of isopeptide bonds, thereby enhancing proteolytic accessibility. Interestingly, keratin degradation by O. corvina was most efficient when using mixed substrates containing both feather and wool meal. These novel insights into the keratinolytic system of O. corvina underscore the importance of considering synergistic enzyme interactions when developing biotechnological approaches for valorization of keratin-rich by-products.