Microbial keratinases: enzymes with promising biotechnological 4 applications

Abstract

SUMMARYKeratin is a complex and structurally stable protein found in human and animal hard tissues, such as feathers, wool, hair, hoof and nails. Some of these, like feathers and wool, represent one of the main sources of protein-rich waste with significant potential to be transformed into value-added products such as feed, fertilizers or bioenergy. A major limitation impeding valorization of keratinous substrates is their recalcitrant structure and resistance to hydrolysis by common proteases. However, specialized keratinolytic enzymes produced by some microorganisms can efficiently degrade these substrates. Keratinases have already found a purpose in pharmaceutical, textile and leather industries. However, their wider implementation in other processes, such as cost-effective (pre)treatment of poultry waste, still requires optimization of production and performance of the available enzymes. Here we present a comprehensive review covering molecular properties and characteristics of keratinases, their classification, traditional and novel approaches in discovery of novel enzymes, production, characterization, improvement and biotechnological applications.

Bacillus cytotoxicus Isolated from a Pristine Natural Geothermal Area Reveals High Keratinolytic Activity

“…Concerning to the production of keratinolytic protease by B. cytotoxicus species, it was observed that keratinases expression was inducible and occurred only in the presence of feathers as an exogenous inducer when it was incubated at 50 • C. Similar inducibility has been found in varieties of microorganisms [27,52,53].…”

“…However, only few thermophilic bacteria are known to produce keratinases. Thus, there is still a need to find more robust and specific thermostable keratinolytic enzymes, which could be applied to fulfill the increasing demand of detergent, leather, textile, food, and pharmaceutical industries [12,[22][23][24][25][26][27][28].…”

Microbial Keratinase: Next Generation Green Catalyst and Prospective Applications

“…Keratinase, on the other hand, displays unique attributes that may be exploited in bioprocessing such as keratin bioconversion to useful products, textile treatment, leather depilation, and other industrial applications (Fang et al, 2013;Kalaikumari et al, 2019). Direct evolution (DE), site-directed mutagenesis (SDM), site-saturation mutagenesis (SSM), truncation, and fusion are among the protein engineering techniques that have been adopted to create robust enzymes (Gong et al, 2015;Yang et al, 2017;Vidmar and Vodovnik, 2018), and it has been successfully applied to overcome the limitations faced with biocatalysts (Fang et al, 2019). Site-directed mutagenesis depends on the protein structure alterations, meanwhile directed evolution functions based on a randomly generated library of mutants for the comprehensive discovery of promising variants (Gupta et al, 2013;Fang et al, 2017b).…”

Revisiting the scope and applications of food enzymes from extremophiles

“…Such enzymatic deconstruction processes are useful during treatment or valorization of polymeric by‐products, treatment of materials for biotechnological applications, and preparation of high‐value hydrolysates from complex polymers. Examples of enzymes that have been used in this category are keratinases for the degradation of recalcitrant keratinous proteins in hair, horns, wool, feathers, hooves, and nails (Vidmar & Vodovnik, 2018). These keratinous materials typically contain over 85% crude proteins (Luan et al., 2019).…”