Tropomyosin(TPM) has a 4-helix coiled structure. It regulates the binding of myosin thus regulating muscle contraction [1]. In its locked conformation it binds troponin T (TnnT) and prevents the binding of myosin to actin. When Ca++ ions bind to TnnT, the TPM assumes an open conformation and myosin can bind to actin. The images on the left and the right correspond to one representative TPM structure, i.e. tropomyosin from pig (1c1g). You can at the right for clarity. The dimers of TPM in the asymmetric unit (1c1g) are , with their C-terminal ends overlapping by about 2/3 of the molecular length. This suggests head-to-tail packing of TPM, which is very important for its interaction with actin [2].
