Sericinis aproteincreated byBombyx mori(silkworms) in the production ofsilk.[1]Silk is a fibre produced by the silkworm in production of itscocoon.It consists mainly of two proteins,fibroinand sericin. Silk consists of 70–80% fibroin and 20–30% sericin; fibroin being the structural center of the silk, and sericin being the gum coating the fibres and allowing them to stick to each other.[2]
Sericin is composed of 18 different amino acids, of which 32% isserine.The secondary structure is usually a random coil, but it can also be easily converted into a β-sheet conformation, via repeated moisture absorption and mechanical stretching. The serine hydrogen bonds give its glue-like quality. The genes encoding sericin proteins have been sequenced. Its C-terminal part contains many serine-rich repeats.[3][4][5]
Usinggamma rayexamination, it was determined that sericin fibers are composed typically of three layers, all with fibers running in different patterns of directionality. The innermost layer, typically is composed of longitudinally running fibers, the middle layer is composed of cross fiber directional patterned fibers, and the outer layer consists of fiber directional fibers. The overall structure can also vary based on temperature, whereas the lower the temperature, there were typically more β-sheet conformations than random amorphous coils. There are also three different types of sericin, which make up the layers found on top of the fibroin. Sericin A, which is insoluble in water, is the outermost layer, and contains approximately 17% nitrogen, along with amino acids such as serine,threonine,aspartic acid,andglycine.Sericin B, composed the middle layer and is nearly the same as sericin A, but also containstryptophan.Sericin C is the innermost layer, the layer that comes closest to and is adjacent to fibroin. Also insoluble in water, sericin C can be separated from the fibroin via the addition of a hot,weak acid.Sericin C also contains the amino acids present in B, along with the addition ofproline.
Sericin has also been used inmedicineandcosmetics.Due to its elasticity and tensile strength, along with a natural affinity forkeratin,sericin is primarily used in medicine for wound suturing. It also has a natural infection resistance, and is used variably due to excellent biocompatibility, and thus is used commonly as a wound coagulant as well.[6]When used in cosmetics, sericin has been found to improve skin elasticity and several anti-aging factors, including an anti-wrinkle property. This is done by minimizing water loss from the skin. To determine this, scientists ran several experimental procedures, including ahydroxyprolineassay, impedance measurements, water loss from the epidermis andscanning electron microscopyto analyze the rigidity and dryness of the skin. The presence of sericin increases hydroxyproline in thestratum corneum,which in turn, decreases skin impedance, thus increasing skin moisture. Adding inpluronicandcarbopol,two other ingredients that can be included in sericin gels, performs the action of repairing natural moisture factors (NMF), along with minimizing water loss and in turn, improving skin moisture.[2]
^Garel A, Deleage G, Prudhomme JC (May 1997). "Structure and organization of the Bombyx mori sericin 1 gene and of the sericins 1 deduced from the sequence of the Ser 1B cDNA".Insect Biochemistry and Molecular Biology.27(5): 469–77.Bibcode:1997IBMB...27..469G.doi:10.1016/S0965-1748(97)00022-2.PMID9219370.
^Takasu Y, Yamada H, Tamura T, Sezutsu H, Mita K, Tsubouchi K (November 2007). "Identification and characterization of a novel sericin gene expressed in the anterior middle silk gland of the silkworm Bombyx mori".Insect Biochemistry and Molecular Biology.37(11): 1234–40.Bibcode:2007IBMB...37.1234T.doi:10.1016/j.ibmb.2007.07.009.PMID17916509.
^Kludkiewicz B, Takasu Y, Fedic R, Tamura T, Sehnal F, Zurovec M (December 2009). "Structure and expression of the silk adhesive protein Ser2 in Bombyx mori".Insect Biochemistry and Molecular Biology.39(12): 938–46.Bibcode:2009IBMB...39..938K.doi:10.1016/j.ibmb.2009.11.005.PMID19995605.
