Helix bundle

A helix bundle is a small protein fold composed of several alpha helices that are usually nearly parallel or antiparallel to each other.

Four-helix bundles typically consist of four helices packed in a coiled-coil arrangement with a sterically close-packed hydrophobic core in the center.

Pairs of adjacent helices are often additionally stabilized by salt bridges between charged amino acids.

Other examples of four-helix bundles include cytochrome, ferritin, human growth hormone, cytokine,[5] and Lac repressor C-terminal.

The four-helix bundle fold has proven an attractive target for de novo protein design, with numerous de novo four-helix bundle proteins having been successfully designed by rational[6] and by combinatorial[7] methods.