Figure 1. Schematic diagram of cMyBP-C localization in the heart.

Cardiac striated muscle in the myocardium is predominantly made up of myofibrils. (A) The sarcomere, which is the functional unit of myofibrils, consists of thick and thin contractile filament proteins. The thick filament proteins are titin, myosin and cMyBP-C, whereas the thin filament proteins are actin, α-TM, cTnT, cTnI and cTnC. The cMyBP-C protein is exclusively expressed in the heart, and it transversely connects both thick and thin filament proteins. (B) cMyBP-C is comprised of 8 immunoglobulin (Ig) and 3 fibronectin type III domains, numbered from the N-terminus as Motifs 0 to 10. In addition, a proline-alanine-rich region is found between the C0 and C1 domains, as well as a phosphorylation motif (M domain), which is found between the C1 and C2 domains. N-terminal regions (C0-C2 domains) interact with thin filament proteins such as actin and thick filament proteins such as myosin S2. C-terminal regions (C8-C10 domains) interact with the thick filament protein titin and the LMM hinge regions.