Coiled Coil

"In a typical coiled-coil two alpha helices wrap around each other to form a stable structure. One side of each helix contains mostly aliphatic amino acids, such as leucines and valines, while the other side contains mostly polar residues. Helices containing distinct hydrophobic and polar sides are called amphipathic. In a coiled-coil, two amphipathic helices are aligned so their hydrophobic sides snuggle tightly together in the center, with their polar faces exposed to the solvent. A triple coiled-coil is another stable structure formed by alpha helices. In this case, three amphipathic helices twist around a central axis. The hydrophobic sides of all three helices face the center of the coil, creating a stable hydrophobic core. Coiled-coils are often found in elongated, fibrous proteins. A triple coiled-coil is the major structural theme in fibrinogen, a protein involved in blood clotting. The fibrous nature of this protein is intimately related to its ability to form clots." Essential Cell Biology, Second Edition by Alberts, Bray, Hopkin, Johnson, Lewis, Raff, Roberts, Walter copyright 2004 by Garland Science Publishing