Figure 1. Effects of Individual N-terminal domains C0, C1 and C2 on TF-activated myosin-S1 ATPase activity.

(a) cMyBP-C is comprised of eight immunoglobulin (Ig)-like and three fibronectin (Fn)-like domains numbered C0 to C10 starting consecutively from the N terminus to the C terminus of the molecule. C0 and C1 domains are connected with the proline/alanine (PA) linker. The M-domain contains phosphorylation sites (PS). (b) Data for C0 and C1 are replotted from [10]. For C0 data were fit by a simple inhibition equation V(C0) = Vo/(1+ ([C0]/K_iC0)), where K_iC0 = 12.1 ± 1 μM and Vo = 0.6 ± 0.1·s⁻¹ is the ATPase rate in the absence of C protein domains. As reported previously [10], C1 shows cooperative activation and inhibition that yields a best fit using V(C1) = V₁/(1 + (K₁/[C1])ⁿ + ([C1]/K_i)ⁿ) + V_o equation, where V₁ = 3.2 ± 0.3 s⁻¹, K_m = 8.4 ± 1 μM, K_i = 15.2 ± 3 μM, n = 2.1 ± 0.3 and V_o = 0.6 ± 0.1·s⁻¹. Experimental conditions were 10 mM mops, 50 mM KAc, 2 mM MgCl₂, 3 mM EGTA (pCa > 8), pH 7.0, 0.65 μM A1S1, 5 μM TFs and the indicated concentration of the N terminal domain subunits of cardiac myosin binding protein C. In the presence of C2 the ATP hydrolysis rate was only partially inhibited at saturating C2 and was fit by V(C2) = V_C2/(1+ ([C2]/K_iC2)) + V₀ where V_C2 = 0.40 s⁻¹ ± 0.1·s⁻¹, K_C2 = 10 ± 2 μM and V₀ = 0.25 ± 05 s⁻¹ is the rate when saturating C2 is bound. Error bars represent SEM.