Fibrous Proteins

Unlike compact globular proteins, fibrous proteins are often located in the extracellular matrix, provide structure, and form extended shapes.

Fibrous proteins are usually composed of either alpha-helices or beta-sheets but rarely a mix of both.

They often have hydrophobic amino acids on their outer surfaces that interact with other monomers to form larger structures.

For example, collagen is a fibrous protein composed of an extended alpha helix.  Three helices wind around each other to make a structure called a coiled-coil. Collagen fibrils provide structure and flexibility in connective tissues.

The protein fibroin is an example of a fibrous protein composed of beta-sheets and is the protein in silk which allows the silk strands to be both flexible and strong.