Coiled Coil Domain Containing Protein 9 (CCDC9)

A coiled coil is a structural motif in proteins, in which 2-7 alpha-helices are coiled together like the strands of a rope. Many coiled coil type proteins are involved in important biological functions such as the regulation of gene expression e.g. transcription factors. Notable examples are the oncoproteins c-fos and jun, and the muscle protein tropomyosin.

Coiled coils usually contain a repeated pattern, hxxhcxc, of hydrophobic and charged amino-acid residues, referred to as a heptad repeat. Folding a sequence with this repeating pattern into an alpha-helical secondary structure causes the hydrophobic residues to be presented as a 'stripe' that coils gently around the helix in left-handed fashion, forming an amphipathic structure. The possibility of coiled coils for α-keratin was proposed by Francis Crick in 1952 as well as mathematical methods for determining their structure.