Coiled coil

From Proteopedia

Coiled Coil Structure: Ribbon Diagram of a Coiled Coil such as occurs in the fibrous proteins alpha-Keratin or tropomyosin.

(KineMage currently not supported) Fibrous proteins are, for the most part, characterized by highly repetitive simple sequences such as a coiled coil of two alpha helices such as occurs in alpha-keratin or tropomyosin. Shown here is a ribbon diagram of a coiled coil. One of the segment's two identical chains, "Coil 1", is yellow and the other, "Coil 2", is seagreen. The N- and C-terminal ends of each segment are marked by blue and red balls. You can readily see that the protein forms a parallel coiled coil: its component alpha helices are right-handed but the coiled coil is left-handed. Look at Views1-3 to see the coiled coil from different angles. Drag the ZClip slide left and right in View3 to see part or all of the structure. Note that the coiled coil makes only slightly more than 1/2 turn over a distance in which each alpha helix makes ~13 turns.

Drag the mouse from side to side horizontally across the image to see the way in which the two coils wrap around each other. Parallel coiled coils occur in many proteins including alpha keratin, a fibrous stress-bearing protein occurring in mammalian skin; tropomyosin and myosin, important proteins in muscle; and the so-called leucine zipper segments that permit the dimerization and hence activation of numerous eukaryotic transcription factors. Leucine zippers differ from other 2-helix coiled coils only in that their d-residues are almost invariably Leu. The coordinates for the coiled-coil (tropomyosin) were obtained from Xiaoling Xia and Carolyn Cohen, Brandeis University;