Figure 4: MetaDynamics simulation of Sac6 loop region with or without T103 phosphorylation.

The free energy surfaces plotted based on two CVs (Rg and C-alpha contact number) for Sac6 N-terminal peptide between the EF hand and ABD1 domain without (a) and with T103 phosphorylation (b). The colour key indicates the scale of free energy values in units of kJ mol⁻¹. (c,e) The representative structures of the three lowest-free-energy clusters. C terminus is indicated by an arrowhead. (d) Free energies of the first 20 lowest-free-energy clusters after reweighting. (f) Contact probability map of the residue side chains in simulated peptides. The interaction possibilities for the residue side chains within T103-phosphorylated and -unphosphorylated peptides are shown in the upper-left and lower-right triangles, respectively. Colour key indicates the range of the interaction probabilities. Blue boxes indicate the positions of phosphorylated and -unphosphorylated T103 (blue box), respectively. Green boxes indicate residues that interact with phosphorylated T103. (g) A model of the conformational changes of Sac6 by T103 phosphorylation. Compared with the unphosphorylated protein, T103 phosphorylation introduces higher stability to the N-terminal EF hand domain for better Sac6 interaction with actin filaments.