Examples of Protein Structures

Fibrous proteins Fibrous proteins tend to be long, narrow molecules. Fibrous proteins are used to construct macroscopic structures, especially structures outside of cells. Fibrous proteins tend to have a structural role, although some have more active functions as well. Examples: The protein α-keratin is used to form hair, nails, and skin. α-Keratin is a coiledcoil of α-helices ~300 residues long (corresponding to about 450 Å in length). αKeratin is formed from two α-helices wrapped around one another (the backbone shown below is of a coiled-coil protein from PDB ID 3Q0X; this portion of the protein probably resembles the keratin coiled-coil structure)), and two of those structures wrapped around each other. Thus the keratin molecule contains a total of four intertwined helices.