Costamere

The costamere or dystrophin-associated protein complex (DAPC) is a structural-functional component of skeletal muscle cells which, according to original descriptions in the early 1980s (which are generally still accepted), are sub-sarcolemmal protein assemblies circumferentially aligned in register with the Z-disk of peripheral myofibrils. They physically couple force-generating sarcomeres with the sarcolemma in striated muscle cells and are thus considered the "Achilles heel", i.e. the key vulnerable point of the muscle which is defective in many myopathies.

The DAPC contains various macromolecules such as dystroglycans which are responsible for linking the DAPC to extracellular proteins; collagen and laminin for example. Therefore it is one of the features of the sarcolemma which helps to couple the sarcomere to the extracellular connective tissue. Desmin protein may also bind to the DAPC, and regions of it are known to be involved in signaling.