Tropomyosin (TPM) has a 4-helix coiled dimer 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 at the top and at the right correspond to one representative TPM structure, i.e. Tropomyosin from pig (1c1g). You can enlarge the image at the right for clarity.
