What is sericin protein and what are its functions?

Sericin protein is a natural macromolecular protein wrapped on the surface of silk fibroin. It is mainly secreted by the silk glands of silkworms and is one of the main proteins that make up the silkworm cocoon. Because of its good water solubility, cell adhesion-promoting and proliferative activities, lower immunogenicity, and unique in situ fluorescence, antioxidant activity, and tyrosinase inhibitory properties, sericin protein is widely used in Fabric finishing coatings, cosmetic additives, as well as food, medicine, functional biological materials.

Table of Sericin

Properties of Sericin Protein

  • Amphoteric properties and isoelectric point of sericin protein
    Sericin contains free shuttle groups and amino groups, which can interact to form bipolar ions and have amphoteric properties. In a solution with a lower pH value, sericin protein exists in the form of positive ions in a solution with a higher value, and sericin protein exists in the form of negative ions. The isoelectric point of sericin protein is: 3.8-4.5.
  • Colloidal properties of sericin protein
    Sericin is a macromolecular compound with a large molecular weight and a particle diameter of 1-100 nm. Since the particle size is in the range of colloidal particles, it shows the unique dialysis, coagulation, Gelling and peptizing properties.
  • The properties of sericin protein denatured
    Sericin molecules often change when they are affected by some external physical or chemical factors, but these changes do not involve changes in the primary structure, and the covalent bond of the peptide chain is not broken, only A change in molecular conformation occurs, resulting in a change in properties. Its main manifestations are changes in physical properties, chemical properties and loss of biological activity, and the most prominent manifestation is the decrease in solubility, which will greatly reduce its use value. The main factors that cause sericin protein denaturation are temperature, pH value and organic solvent.
  • Swelling and dissolving of sericin protein
    Sericin is a kind of macromolecule. When it comes into contact with an appropriate liquid, it will automatically absorb the liquid and swell and become soft. After infinite swelling, it can dissolve in the liquid. In general, silk fibroin can only swell but not dissolve in water, but sericin can dissolve in hot water. This is the most important property of sericin protein, and it is also the basis for people to use water to make silk, scouring and degumming.
sericin protein

Pharmacological Effects

Sericin protein is similar to the natural moisture-regulating factor in the stratum corneum of human skin, which can maintain the right amount of water in the skin and make the skin smooth, soft and elastic. Sericin and its hydrolyzate are also a natural antioxidant. The ability to inhibit fat peroxidation is comparable to that of VC. It also has the effect of inhibiting tyrosinase activity. When the concentration of sericin protein is 0.5%, it has the ability to inhibit tyrosinase activity. Even if heated and boiled, the two above-mentioned activities remain unchanged. Therefore, this inhibitor with natural antioxidant and tyrosine activity is safe, effective, stable and inexpensive, and has broad application prospects in the fields of medicine, cosmetics, food additives and so on. In addition, sericin was also found to be an activity enhancer of high temperature DNA polymerase. In the presence of high-temperature DNA polymerase in the DNA amplification reaction system (generation) R, adding 0.1 mg/mL-2.0 mg/mL, and stopping the sericin solution, not only can significantly promote this high-temperature DNA polymerase The polymerase activity can be reduced, and the amount of this polymerase can be reduced for efficient low-dose DNA amplification.

Water-soluble sericin protein and its hydrolyzate have obvious curative effect on certain skin diseases. Sericin is also a good anti-inflammatory agent for the treatment of certain skin diseases. When sericin is mixed with yeast extract obtained by enzymatic or acid hydrolysis, it can also become a new topical ointment for skin. This topical cream can also promote collagen production in dermal fibroblasts, effectively preventing or slowing down various skin conditions such as skin wrinkling and aging, decreased elasticity, roughness, blackening, and relaxation. In addition, sericin can be mixed with xyloglucan, ultraviolet absorber, thickening agent mucopolysaccharide and hexaoxyethylene polymer or its derivatives to make another topical ointment.

The non-essential amino acid serine secreted by cerebrospinal astrocytes is necessary for the survival and growth of brain neurons], and glial cells promote the survival and development of central neuron cells through the supply of trophic factors. Glycine, like L-serine, is also a trophic factor produced by glial cells, which can promote the survival, dendrites and electrophysiological development of cultured neurons in the cerebellum. In sericin protein, L-serine accounts for 33%, while glycine contains 16%, which together account for about half of the total. Therefore, more intake of sericin protein and its hydrolyzate is beneficial to improve human memory, prevent brain aging, and prevent dementia. Therefore, sericin and its hydrolyzate have appeared as additives for dietary water or cooking water. It can inhibit auto-oxidation, and when added to food, it not only plays the role of sterilization and antiseptic, but also can make the food quality stable, delicious and long-term preservation. Long-term drinking or consumption of water with sericin protein to make food, rice, tea, beverages, etc. can maintain health, inhibit bacteria, delay aging, and beautify the skin.

Sericin protein and its hydrolyzate can inhibit the growth of Escherichia coli, and contribute to the improvement of intestinal physiological function and the enhancement of human body constitution.

According to the function of amino acids, glycine and serine can reduce the content of cholesterol in the blood, excrete harmful substances in the human body, and have a detoxification effect. Sericin protein is also the main component of a hypoglycemic drug.

Sericin protein and its hydrolyzate have obvious inhibitory effect on colorectal cancer.

Sericin protein or silk fibroin can be made into another anticoagulant by sulfated treatment. Add concentrated sulfuric acid to the sericin protein or silk fibroin solution, the amount of which is 0.5 to 500 times the amount of sericin protein or silk fibroin. The sulfated sericin protein or silk fibroin product was obtained, filtered, washed, dissolved in water, dialyzed, freeze-dried, and finally a water-soluble sulfated sericin protein or silk fibroin powder was obtained. Like heparin, it has anticoagulant activity, while unsulfated sericin protein or silk fibroin has no such anticoagulant activity. Therefore, sulfated sericin protein or silk fibroin can replace heparin, which has the characteristics of low price, high production efficiency and high safety. Anticoagulation treatment on the surface of medical materials that come into contact with blood during examination or treatment.

Sericin protein and acrylic acid (PAA) are polymerized to make a novel mucoadhesive polymer.

Silk protein can be dissolved in haloacetic acid to make non-toxic, transparent and homogeneous artificial organs and medical biological materials.

The artificial skin made of amorphous silk fibroin film can not only speed up the repair of skin wounds, but also be easy to peel off and not easily adhere to the new skin. This silk fibroin membrane has good moisture permeability, and the healing time after covering the wound is significantly earlier, which can promote the growth of epidermal cells.

The silk protein membrane made from the mixture of sericin protein and silk fibroin has good oxygen permeability, and its performance is similar to that of human cornea. It is expected to be used in artificial cornea. This membrane is also an effective culture substrate for cell proliferation and can replace collagen.

The hydrogel made of sericin protein or silk fibroin mixed with polyvinyl alcohol (VP) A has excellent absorption, moisture release and elasticity.

Separation of Sericin Protein

  • High temperature hot water method
    That is, by soaking silk in hot water, sericin is dissolved in hot water and silk fibroin is insoluble. Then, the silk fibroin is removed by filtration or centrifugation to obtain an aqueous solution of sericin protein. The sericin solution is then dried to obtain sericin protein powder. The sericin obtained by this method does not introduce other chemicals, but the yield is lower.
  • Sodium carbonate method
    The silk is immersed in an aqueous solution of sodium carbonate. At a certain temperature, sericin protein is dissolved in the aqueous solution of sodium carbonate, while silk fibroin does not dissolve. The silk fibroin is removed by filtration or centrifugation, and then the obtained sodium carbonate sericin aqueous solution is dialyzed, concentrated or dried to obtain sericin protein.
  • Acid precipitation method
    Utilizing the characteristics of sericin protein’s reduced solubility at the isoelectric point (pH 3.8-4.5), sericin protein is precipitated from the aqueous solution, and then recycled and used. This method is one of the most commonly used methods for separating proteins in industry.
  • Citric acid method
    Sericin protein can be obtained by dialysis and concentration of the dissolved sericin citric acid solution by utilizing the property that sericin protein can be dissolved in boiling water of citric acid aqueous solution, while silk fibroin is insoluble. However, in this method, the protein is precipitated from the solution during dialysis, and the precipitated sericin protein is difficult to reconstitute.
  • Urea method
    A method in which sericin is obtained by dissolving sericin protein in aqueous urea solution, and then dialysis and concentration. The effect of this method on the molecular weight of sericin protein is much lighter than that of the high temperature hot water method and the sodium carbonate method. However, the sericin protein obtained by this method has obvious cytotoxicity.
  • Lithium bromide method
    This method uses lithium bromide aqueous solution to dissolve sericin protein at a lower temperature, and then dialyses and concentrates to obtain an ideal concentration of sericin aqueous solution. This method is a relatively mild method reported so far to separate sericin protein from silk.

Application of Sericin Protein


“Sericin”Cytokines and Cells Online Pathfinder Encyclopedia. January 2008

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