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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.
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.
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.
