Production and characterization of bio-immobilized keratinase in proteolysis and keratinolysis

Enhancement of Activity and Thermostability of Keratinase From Pseudomonas aeruginosa CCTCC AB2013184 by Directed Evolution With Noncanonical Amino Acids

A keratinase from Pseudomonas aeruginosa (KerPA), which belongs to the M4 family of metallopeptidases, was characterised in this study. This enzyme was engineered with non-canonical amino acids (ncAAs) using genetic code expansion. Several variants with enhanced activity and thermostability were identified and the most prominent, Y21pBpF/Y70pBpF/Y114pBpF, showed an increase in enzyme activity and half-life of approximately 1.3-fold and 8.2-fold, respectively. Considering that keratinases usually require reducing agents to efficiently degrade keratin, the Y21pBpF/Y70pBpF/Y114pBpF variant with enhanced activity and stability under reducing conditions may have great significance for practical applications. Molecular Dynamics (MD) was performed to identify the potential mechanisms underlying these improvements. The results showed that mutation with pBpF at specific sites of the enzyme could fill voids, form new interactions, and reshape the local structure of the active site of the enzyme.

Microbial keratinase and the bio-economy: a three-decade meta-analysis of research exploit

Microbial keratinase research has been on an upward trajectory due to the robustness and efficiency of the enzyme toward various green technological processes that promote economic development and environmental sustainability. A compendium of research progression and advancement within the domain was achieved through a bibliometric study to understand the trend of research productivity, scientific impacts, authors' involvement, collaboration networks, and the advancement of knowledge gaps for future research endeavours. A three-decade (1990 to 2019) scholarly published articles were retrieved from the web of science database using a combination of terms "keratinas* or keratinolytic proteas* or keratinolytic enzym*", and subsequently analyzed for bibliometric indicators. A collection of 330 peer-reviewed, research, articles were retrieved for the survey period and authored by 1063 researchers with collaboration index of 3.27. Research productivity was most in 2013 with total research output of 28 articles. The top three authors' keywords were keratinase, keratin and protease with a respective frequency of 188, 26 and 22. India, China and Brazil ranked top in terms of keratinase research outputs and total citation with respective article productivity (total citations) of 85 (1533), 57 (826), and 36 (764). This study evaluated the trend of keratinase research outputs, scientific impact, collaboration networks and biotechnology innovations. It has the potentials to influence positively decision making on future research direction, collaborations and development of products for the bio-economy.

Microbial keratinases: industrial enzymes with waste management potential

Proteases are ubiquitous enzymes that occur in various biological systems ranging from microorganisms to higher organisms. Microbial proteases are largely utilized in various established industrial processes. Despite their numerous industrial applications, they are not efficient in hydrolysis of recalcitrant, protein-rich keratinous wastes which result in environmental pollution and health hazards. This paved the way for the search of keratinolytic microorganisms having the ability to hydrolyze "hard to degrade" keratinous wastes. This new class of proteases is known as "keratinases". Due to their specificity, keratinases have an advantage over normal proteases and have replaced them in many industrial applications, such as nematicidal agents, nitrogenous fertilizer production from keratinous waste, animal feed and biofuel production. Keratinases have also replaced the normal proteases in the leather industry and detergent additive application due to their better performance. They have also been proved efficient in prion protein degradation. Above all, one of the major hurdles of enzyme industrial applications (cost effective production) can be achieved by using keratinous waste biomass, such as chicken feathers and hairs as fermentation substrate. Use of these low cost waste materials serves dual purposes: to reduce the fermentation cost for enzyme production as well as reducing the environmental waste load. The advent of keratinases has given new direction for waste management with industrial applications giving rise to green technology for sustainable development.

High-level expression of Proteinase K from Tritirachium album Limber in Pichia pastoris using multi-copy expression strains

Proteinase K is widely used in scientific research and industries. This report was aimed to achieve high-level expression of proteinase K using Pichia pastoris GS115 as the host strain. The coding sequence of a variant of proteinase K that has higher activity than the wild type protein was chosen and optimized based on the codon usage preference of P. pastoris. The novel open reading frame was synthesized and a series of multi-copy expression vectors were constructed based on the pHBM905BDM plasmid, allowing for the tandem integration of multiple copies of the target gene into the genome of P. pastoris with a single recombination. These strains were used to study the correlation between the gene copy number and the expression level of proteinase K. The results of quantitative polymerase chain reaction (qPCR) indicated that the tandem expression cassettes were integrated into the host genome stably. Meanwhile, the results of qPCR and enzyme activity assays indicated that the mRNA and protein expression levels of the target gene increased as the gene copy number increased. Moreover, the effect of gene dosage on the expression level of the recombinant protein was more obvious using high-density fermentation. The maximum expression level and enzyme activity of proteinase K, which were obtained from the recombinant yeast strain bearing 5 copies of the target gene after an 84-h induction, were approximately 8.069 mg/mL and 108,295 U/mL, respectively. The recombinant proteinase was purified and characterized. The optimum pH and temperature for the activity of this protease were approximately pH 11 and 55 °C, respectively.

Production of feather hydrolysates with antioxidant, angiotensin-I converting enzyme- and dipeptidyl peptidase-IV-inhibitory activities

The antioxidant and antihypertensive activities of feather hydrolysates obtained with the bacterium Chryseobacterium sp. kr6 were investigated. Keratin hydrolysates were produced with different concentrations of thermally denatured feathers (10-75 g l(-1)) and initial pH values (6.0-9.0). Soluble proteins accumulated in high amounts in media with 50 and 75 g l(-1) of feathers, reaching values of 18.5 and 22 mg ml(-1), respectively, after 48 hours of cultivation. In media with 50 g l(-1) of feathers, initial pH had minimal effect after 48 hours. Maximal protease production was observed after 24 hours of cultivation, and feather concentration and initial pH values showed no significant effect on enzyme yields at this time. Feather hydrolysates displayed in vitro antioxidant properties, and optimal antioxidant activities were observed in cultures with 50 g l(-1) feathers, at initial pH 8.0, after 48 hours growth at 30°C. Also, feather hydrolysates were demonstrated to inhibit the angiotesin I-converting enzyme by 65% and dipeptidyl peptidase-IV by 44%. The bioconversion of an abundant agroindustrial waste such as chicken feathers can be utilized as a strategy to obtain hydrolysates with antioxidant and antihypertensive activities. Feather hydrolysates might be employed as supplements in animal feed, and also as a potential source of bioactive molecules for feed, food and drug development.

Biotechnological applications and prospective market of microbial keratinases

Keratinases are well-recognized enzymes with the unique ability to attack highly cross-linked, recalcitrant structural proteins such as keratin. Their potential in environmental clean-up of huge amount of feather waste has been well established since long. Today, they have gained importance in various other biotechnological and pharmaceutical applications. However, commercial availability of keratinases is still limited. Hence, to attract entrepreneurs, investors and enzyme industries it is utmost important to explicitly present the market potential of keratinases through detailed account of its application sectors. Here, the application areas have been divided into three parts: the first one is dealing with the area of exclusive applications, the second emphasizes protease dominated sectors where keratinases would prove better substitutes, and the third deals with upcoming newer areas which still await practical documentation. An account of benefits of keratinase usage, existing market size, and available commercial sources and products has also been presented.

Control of protein immobilization: coupling immobilization and site-directed mutagenesis to improve biocatalyst or biosensor performance

Mutagenesis and immobilization are usually considered to be unrelated techniques with potential applications to improve protein properties. However, there are several reports showing that the use of site-directed mutagenesis to improve enzyme properties directly, but also how enzymes are immobilized on a support, can be a powerful tool to improve the properties of immobilized biomolecules for use as biosensors or biocatalysts. Standard immobilizations are not fully random processes, but the protein orientation may be difficult to alter. Initially, most efforts using this idea were addressed towards controlling the orientation of the enzyme on the immobilization support, in many cases to facilitate electron transfer from the support to the enzyme in redox biosensors. Usually, Cys residues are used to directly immobilize the protein on a support that contains disulfide groups or that is made from gold. There are also some examples using His in the target areas of the protein and using supports modified with immobilized metal chelates and other tags (e.g., using immobilized antibodies). Furthermore, site-directed mutagenesis to control immobilization is useful for improving the activity, the stability and even the selectivity of the immobilized protein, for example, via site-directed rigidification of selected areas of the protein. Initially, only Cys and disulfide supports were employed, but other supports with higher potential to give multipoint covalent attachment are being employed (e.g., glyoxyl or epoxy-disulfide supports). The advances in support design and the deeper knowledge of the mechanisms of enzyme-support interactions have permitted exploration of the possibilities of the coupled use of site-directed mutagenesis and immobilization in a new way. This paper intends to review some of the advances and possibilities that these coupled strategies permit.

Processing of poultry feathers by alkaline keratin hydrolyzing enzyme from Serratia sp. HPC 1383

The present study describes the production and characterization of a feather hydrolyzing enzyme by Serratia sp. HPC 1383 isolated from tannery sludge, which was identified by the ability to form clear zones around colonies on milk agar plates. The proteolytic activity was expressed in terms of the micromoles of tyrosine released from substrate casein per ml per min (U/mL min). Induction of the inoculum with protein was essential to stimulate higher activity of the enzyme, with 0.03% feathermeal in the inoculum resulting in increased enzyme activity (45U/mL) that further increased to 90U/mL when 3d old inoculum was used. The highest enzyme activity, 130U/mL, was observed in the presence of 0.2% yeast extract. The optimum assay temperature and pH for the enzyme were found to be 60 degrees C and 10.0, respectively. The enzyme had a half-life of 10min at 60 degrees C, which improved slightly to 18min in presence of 1mM Ca(2+). Inhibition of the enzyme by phenylmethyl sulfonyl fluoride (PMSF) indicated that the enzyme was a serine protease. The enzyme was also partially inhibited (39%) by the reducing agent beta-mercaptoethanol and by divalent metal ions such as Zn(2+) (41% inhibition). However, Ca(2+) and Fe(2+) resulted in increases in enzyme activity of 15% and 26%, respectively. The kinetic constants of the keratinase were found to be 3.84 microM (K(m)) and 108.7 microM/mLmin (V(max)). These results suggest that this extracellular keratinase may be a useful alternative and eco-friendly route for handling the abundant amount of waste feathers or for applications in other industrial processes.

Immobilization of Endoproteases from Crude Extract of Cynara cardunculus L. Flowers

The cardoon (Cynara cardunculus L.) is a variety of thistle which grows wild and abundantly in uncultivated areas of many regions of Portugal. Its dried flowers are used as a milk coagulant in the manufacture of traditional cheeses, due to its high content in aspartic proteases, namely cardosins A and B. In general, proteases can be immobilized without significant loss of their catalytic activity and their use as milk coagulant offers several advantages over their soluble counterparts, namely simplified protocols, long term stability of the coagulant and successful reutilization. Since proteases are often expensive, especially at high degrees of purity, immobilization may increase their industrial applicability. In this work, aqueous extracts of cardoon were immobilized on celite by adsorption. The properties of free and immobilized extracts from cardoon (kinetic parameters, pH effects, activation energy, ionic effects, clotting time) were compared. Optima pH and temperature were 5.0 and 60 °C, respectively, for extracts in both forms. Upon immobilization, a 60—70% loss of enzyme activity, as well as a decrease in the specificity constants (up to 90%) were observed. Immobilized biocatalyst was evaluated for bovine and caprine caseins, at a laboratory scale, showing a higher specificity towards the latter.

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.