The TTN gene codes for the largest known protein in the human body, titin. This protein, which is also known as connectin, is found in sarcomeres, the basic units of striated muscle tissue. The protein is made up of the elastic I-band at the N-terminal and the kinase A-band at the C-terminal. It connects the Z-line to the M-line in the sarcomere, by binding its N-terminal Z-disc region and its C-terminal M-line region to the Z-line and M-line respectively. The titin protein thus spans half the length of the sarcomere and acts as a molecular spring responsible for the elasticity of muscles. It acts along with myosin and actin to keep the components of the sarcomere in place and is necessary for the stability and flexibility of the unit. The protein also contains sites for binding with other proteins, is involved in chemical signaling, and is speculated to function in chromosome condensation during mitosis.
The gene is implicated in several disorders of myopathy and muscular dystrophy. It has been associated with Cardiomyopathy, Dilated, 1G (CMD1G), Cardiomyopathy, Familial Hypertrophic, 9 (CMH9), Muscular Dystrophy, Limb-Girdle, Type 2J (LGMD2J), Myopathy, Early-Onset, with Fatal Cardiomyopathy (EOMFC), Hereditary Myopathy with Early Respiratory Failure (HMERF) and Tibial Muscular Dystrophy, Tardive (TMD).