Figure 2

In vitro motility assays demonstrate MyBP-C regulation by promoting and inhibiting motility of native thin filaments (NTFs) at low and high Ca²⁺, respectively. (A–C) Control NTFs (grey line) show a sigmoidal increase in activation in response to increasing calcium levels. C0C2, fsC1C2, and ssC1C2 (0.25 µM) all shift this response to the left, indicating an increased activation effect at lower Ca²⁺ levels. (A) C0C2 activates NTF sliding velocities at both low Ca²⁺ levels and inhibits NTF motility at high Ca²⁺ levels. (B) fsC1C2 is unable to activate NTF motility at low Ca²⁺ levels, but inhibits NTF motility at higher Ca²⁺ levels. (C) Conversely, ssC1C2 activates NTF motility at low Ca²⁺ levels, but lacks the capacity to limit NTF motility at high Ca²⁺ levels. Effects of MyBP-C N-termini varied, depending on concentration, as demonstrated by dose-dependent responses of C0C2, fsC1C2, and ssC1C2 on NTF motility at (D) pCa 9 (E) pCa 6.75 and (F) pCa 5. Graphs represented as mean ± SEM.