CATH: 1.20.5

The motif is characterized by a unique, compact spatial arrangement consisting of three consecutive helices connected by irregular loop regions. The connecting loops vary in length from 2 to 28 amino acids. Typically, three-helix bundle structures are approximately 80 amino acids in length. This motif features a pronounced hydrophobic core, with both hydrogen bonds and hydrophobic interactions stabilizing its three-dimensional structure.

The three-helix bundle is a common fold found in small proteins as well as in domains of larger homologous and non-homologous proteins. It is present in diverse protein classes, including DNA-binding proteins, enzymes, lysine-rich proteins, and enzyme inhibitors. Furthermore, the three-helical bundle often functions as a structural subdomain within the tertiary structure of many large proteins.