The retro-GCN4 leucine zipper sequence forms a stable three-dimensional structure

The question of whether a protein whose natural sequence is inverted adopts a stable fold is still under debate. We have determined the 2.1-Angstrom crystal structure of the retro-GCN4 leucine zipper. In contrast to the two-stranded helical coiled-coil GCN4 leucine zipper, the retro-leucine zipper formed a very stable, parallel four-helix bundle, which now lends itself to further structural and functional studies.