The connective tissue found in skin is an intricate mesh of interacting protein molecules that constitute the extracellular matrix. The main types of proteins that make up the matrix include collagens, elastin, fibronectin and laminin.

Collagens are a family of fibrous proteins that are the most abundant proteins in mammals, constituting about 25 percent of their total protein. Elastin, present in elastic fibers of tissues such as blood vessels and skin, gives these tissues the ability to recoil after stretching. Elastin in its native state is an extensively cross-linked polypeptide having a peculiar chemical composition. Approximately one third of the amino acids in elastin are glycine, 10-13 percent are proline, and over 40 percent are other amino acids with hydrophobic side chains. Laminin is a major component of basement membranes made by epithelial cells. Laminin is composed of three different subunits in a cross-linked structure. Fibronectin is a cell-surface and blood glycoprotein. It is present in an insoluble form at the cell surface and in connective tissue and in a soluble form in plasma.

Components of the extracellular matrix of animals have been often incorporated into cosmetic compositions. In some instances, normally cross-linked and insoluble proteins such as elastin are rendered soluble using a variety of chemical and enzymatic methods. The rationale behind these procedures is that soluble elastin derivatives will penetrate into the skin to a greater degree than cross-linked elastin to compensate for loss of elastin during skin aging. However, the chemical and enzymatic methods used in solubilization induce extensive chemical and structural changes in the elastin molecule itself. In addition the soluble precursor of insoluble elastin, called tropoelastin, is very difficult to extract and is destroyed during the use of conventional methods for solubilizing elastin.

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Another consideration affecting the use of proteins such as elastin as cosmetic ingredients concerns the degree to which the proteins produce unwanted allergic responses in the skin. This is particularly troublesome since the elastin used in most cosmetics is derived from the neck tendons of young calves or other mammals. Non-human sources of many proteins are potent allergens and cannot be used in unmodified form in humans. The use of authentic human extracellular matrix proteins in cosmetics could avoid these problems. A biotechnology based process to manufacture human elastin or tropoelastin provides a unique, functional source of this matrix protein for cosmetic compositions. The material displays several properties that make it far superior to any conventional source of this material.

Elastin. The elastic properties of the skin, lungs, arteries and other organs are due to the presence of an extracellular matrix of elastic fibers composed primarily of the protein elastin. This protein is synthesized inside cells and incorporated into tissues surrounding the cells to form layers of elastic fibers. These fibers help provide strength and flexibility to tissue structures. The ability of cells to synthesize elastin declines with age and this decline may contribute to the formation of wrinkles in the skin. Elastin synthesis in the cells results in a protein with a molecular weight of approximately 72,000 composed of a structural protein and signal peptide, termed tropoelastin. This protein is processed after synthesis by cleavage of the signal peptide via a signal peptidase and the formation of crosslinks between individual elastin molecules through the action of the enzyme lysyl oxidase to form a tissue matrix.