Microbial keratinases and their prospective applications: an overview

Microbial keratinases have become biotechnologically important since they target the hydrolysis of highly rigid, strongly cross-linked structural polypeptide "keratin" recalcitrant to the commonly known proteolytic enzymes trypsin, pepsin and papain. These enzymes are largely produced in the presence of keratinous substrates in the form of hair, feather, wool, nail, horn etc. during their degradation. The complex mechanism of keratinolysis involves cooperative action of sulfitolytic and proteolytic systems. Keratinases are robust enzymes with a wide temperature and pH activity range and are largely serine or metallo proteases. Sequence homologies of keratinases indicate their relatedness to subtilisin family of serine proteases. They stand out among proteases since they attack the keratin residues and hence find application in developing cost-effective feather by-products for feed and fertilizers. Their application can also be extended to detergent and leather industries where they serve as specialty enzymes. Besides, they also find application in wool and silk cleaning; in the leather industry, better dehairing potential of these enzymes has led to the development of greener hair-saving dehairing technology and personal care products. Further, their prospective application in the challenging field of prion degradation would revolutionize the protease world in the near future.