title: Effects of C-protein on synthetic myosin filament structure.
abstract: In the absence of C-protein, synthetic filaments prepared from column-purified myosin exhibit the following features: individual filament diameters are uniform over a long length, but a wide distribution of diameters is apparent over the population; approximately 25% of the filaments have a frayed appearance and take up stain poorly, whereas the remaining 75% are well-stained; optical diffraction of well-stained filaments reveals a 14.3-nm subunit period and a 43-nm axial period (Koretz, 1978; Koretz, 1979). Addition of C-protein to myosin before filament formation affects all of these features in a manner related to C-protein concentration. At the physiological ratio of C-protein to myosin in the banded region of the natural thick filament, synthetic aggregates are uniform in diameter over the population and show less than 10% frays. Whereas the subunit period remains unchanged, the axial period has increased to 114.4 nm, or eight times the subunit repeat. Above and below the physiological ratio, disorder of a specific nature is apparent. Addition of C-protein after filament formation appears to coat the aggregates so that elements of backbone ultrastructure are obscured, and some evidence of axial period change is visible in diffraction patterns. A model is presented for the binding of C-protein to myosin, and its observed effects on filament structure are explained in terms of this model.
mesh_terms: D002352:Carrier Proteins; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003599:Cytoskeleton / Q000187:drug effects / Q000648:ultrastructure*; D003956:Dialysis; D008854:Microscopy, Electron; D009124:Muscle Proteins / Q000494:pharmacology*; D009218:Myosins / Q000302:isolation & purification; D000099163:Myosin Binding Protein C
chemical_list: D002352:Carrier Proteins; D009124:Muscle Proteins; D009218:Myosins; D000099163:Myosin Binding Protein C
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