The carboxyl terminus of myosin binding protein C (MyBP-C, C-protein) specifies incorporation into the A-band of striated muscle

摘要: Myosin binding protein-C (MyBP-C), also known as C-protein, is a major constituent of the thick filaments vertebrate striated muscles. The protein, approximately 130 kDa, consists series 10 globular motifs (numbered I to X) each 90–100 amino acids, bearing resemblance C2-set immunoglobins (Ig C2) and fibronectin type III (FnIII) motifs. Using pure preparations myosin MyBP-C, it has been demonstrated that domain MyBP-C resides within C-terminal Ig C2 motif (motif X). However, in context vivo filament, uncertain if latter sufficient target correctly A-band or other regions molecule are required for this process. To answer question, cultures skeletal muscle myoblasts were transfected with expression plasmids encoding seven truncation mutants their targeting investigated by immunofluorescence microscopy. distinguish recombinant proteins from endogenous myc epitope was inserted at terminus. Recombinant exhibited an identical distribution sarcomere native MyBP-C; i.e. found exclusively C-zone A-band. A mutant 372 but lacking I-VI (termed delta 1–6), targeted This fragment, which composed two FnIII motifs, minimal protein fragment correct incorporation. Larger amino-terminal deletions deletion X, domain, abolished all localization One construct (delta 10) only X strongly inhibited myofibril assembly. We conclude although essential, not incorporation into VII IX data suggest topological model associated filament through its C