Fibrous proteins, also called scleroproteins, are long filamentous protein molecules that form one of the two main classes of protein (the other being globular proteins). Fibrous proteins are only found in animals and are pratically water-insoluble.

Structural role

Unlike globular proteins, fibrous ones are never enzymes, hormones or any regulatory molecules. Instead, they play a structural and constitutive role. According to where they are found in the organism, fibrous proteins are subdivided into 3 different types:

• Keratins form protecting tissues of the body, such as the epidermis, the hair, fingernails (alpha keratins) as well as bird feathers (beta keratins).
• Collagens constitute connective tissues like cartilages.
• Elastins, also present at connective tissues, are mainly found at blood vessels or ligaments.
• Different kinds of fibroins found in silks, cocoons or spiderwebs.

If alpha helices serve as basic secondary structure at keratins and collagens, silk proteins on the contrary are constituted of beta sheets, which when accumulated cause the solidity of silks. Moreover, the more disulfide bonds the protein has, the more rigid it is.