Keratinase is a protease that can specifically degrade keratin. Keratinase is an inducible enzyme that is synthesized only when an inducer (keratin) appears in the environment. Keratinase can be produced by many kinds of microorganisms, and has broad application prospects in the fields of feed, leather, medicine, food and other industrial, as well as environmental governance.
Sources
As early as the beginning of the 19th century, people discovered that some organisms could degrade keratin, and the separation of such strains has been ongoing since then. At present, there are more than 30 kinds of microorganisms that can degrade keratin, including bacteria, actinomycetes and fungi, such as Dermatophyte and Cnadina albicans in fungi, Streptomyces in actinomycetes, Bacillus licheniformis and Bacillus subtilis in bacteria, etc. The keratinase produced by different microorganisms has a certain difference, mainly in terms of the existence of the enzyme, as well as the structure, composition, stability, optimum reaction temperature, and pH value of the enzyme. For example, some forms of keratinase exist mainly in the cell, and some of them are mainly secreted to the outside. The keratinase of the fungus is found both intracellularly and extracellularly.
Properties
The molecular weight of keratinase that has been isolated and purified is quite different, ranging from dozens of kDa to several hundred kDa. The smaller keratinase is a monomeric enzyme with a molecular weight of 18 kDa; the larger one is a complex enzyme, such as keratinase produced by thermophilic anaerobic bacteria, whose molecular weight is up to 200 kDa or more. The molecular weight of most keratinases is concentrated between 30 and 70 kDa. In addition to keratin, keratinase can also hydrolyze a variety of protein substrates, including soluble and insoluble proteins. Keratinase can degrade soluble proteins such as casein, gelatin, and bovine serum albumin. It also degrades insoluble proteins including feathers, wool, keratin, human hair, and nails. The optimal reaction pH of keratinase is mostly neutral to alkaline, usually between 7 and 10. The optimum pH of some keratinase can reach about 12. Acid keratinase is relatively less, most of which are from fungi. The optimum reaction temperature of keratinase is generally 40°C to 60°C.
Catalytic Mechanism
The mechanism by which microorganisms degrade keratin varies, so the product during degradation is not the same. Some fungi reduce the disulfide bonds through the sulfites secreted on the surface of the mycelia and the acidic environment, while Streptomyces through the production of intracellular reductase. However, water-insoluble keratin can only exist extracellularly in the form of particles. Therefore, the reduction of disulfide bonds can only occur outside the whole cell with strong metabolic ability, most likely in the cell-bound redox system on the cell surface because it requires insoluble keratin in close contact with cells. Observations of pure white high-temperature actinomycetes revealed that the disulfide bond reduction was performed by a cell-linked redox system. No sulfhydryl groups were detected during keratolysis of S. freundii and B. licheniformis. This may be due to the fact that the cysteine (-SH) produced by the reduction of the cystine disulfide bond was quickly converted to other product.
Keratinase actually has the activity of disulfide reductase and polypeptide hydrolase. At present, it is generally believed that the degradation process of keratinase is divided into three steps, namely denaturation, hydrolysis and transamination. First, the disulfide reductase acts on the keratin disulfide bond to reduce cystine (-S-S-) to cysteine (-SH), so that the high-level structure of keratin disintegrates to form degenerative keratin protein. The degenerative keratin protein is gradually hydrolyzed into polypeptides, oligopeptides and free amino acids by the action of polypeptide hydrolase. Finally, ammonia and sulfide are produced by transamination to completely hydrolyze keratin.
Applications
In agriculture, keratinase produced by microorganisms can degrade keratin into polypeptides and amino acids, which can be used to make organic fertilizers. The organic fertilizer not only solves the problem of energy shortage, but also degrades the sources of pollution and greatly improves the environment.
In the feed industry, the main component of feathers is keratin, which has a crude protein content of more than 80%. The animal has a complete range of essential amino acids, which is a good source of feed protein that can replace or partially replace fish meal. Therefore, the development and utilization of waste feathers have important application prospects. On the one hand, it solves the problem of insufficient protein resources in the current feed industry, as well as can solve the problem of environmental pollution.
Keratinase can also be used in cosmetics and medicine industry. Keratinase is an important invasive factor of dermatophytes. Therefore, whether keratinase inhibitors or keratinase monoclonal antibodies can inhibit the action of keratinase, weaken the invasiveness of dermatophytes, and achieve the purpose of treating skin fungal infections is an important research direction of keratinase and dermatophyte infection. Keratinase has highly efficient keratin hydrolyzing activity. The use of keratinase to improve the permeability of drugs in keratin can improve the efficacy of skin external medicine.
