Leucine zipper: A structural motif in the presence of DNA-binding proteins and other proteins. A leucine zipper is formed when the hydrophobic faces of two dual-purpose alpha-helices (often containing leucine residues) from the same or different polypeptide chains interact to form a loop-to-circle dimer structure. .
The leucine zipper is composed of stretched amino acids. The seventh amino acid in every 7 amino acids is leucine, and the leucine is a hydrophobic amino acid. On one side of the helix, all charged amino acid residues are on the other side. When two protein molecules are arranged in parallel, the leucines interact to form a dimer, forming a "zipper." In a "zipper" type protein molecule, a charged amino acid form other than leucine binds to DNA.