Figure 5
From: Differences in the mechanical unfolding pathways of apo- and copper-bound azurins
Comparison of unfolding of apo- and holo-azurins. (A) Copper coordination sphere in holo-azurin. (B) 2D topology showing inter-residue separations of the copper coordination sphere and those of the β4–β7 strand pair. (C) (Top three panels) Simulated FX traces (10 simulations) of three different forms of apo-azurin, ‘no axial’ holo-azurin, and holo-azurin. (Bottom) GC-GC distance change of adjacent β-strands as a function of C-terminal pulling of holo-azurin. All copper-ligand coordination bonds in holo-azurin and three planar equatorial copper-ligand bonds in ‘no axial’ holo-azurin were kept at a spring constant 25 kcal/mol/Å2 (see text for more details). Comparison of peak positions in FX-traces (reference dotted lines show peak positions for holo-azurin) shows that the position of the second TS peak is shifted to shorter extensions due to the presence of copper in accord with experimentally observed changes in ΔLc (Fig. 4B). Corresponding peak positions and inter-peak separations are reported in Table S6. (D) Inter-residue distance (Cα-Cα separation) change for residue pairs shown in Fig. 5B during unravelling of different forms of azurin. Thin vertical line represents the position of the second TS for holo-azurin. Thin horizontal line represents the separation of residue pair Gly45-Met121 in apo-azurin. Intersection of these two thin lines explains the larger ΔLc for the Iapo relative to that of Iholo. Note that for the ‘no axial’ model, Gly45-Met121 pair separates less relative to apo-azurin thereby producing an intermediate ΔLc between that of apo- and holo-azurins. Corresponding GC-GC distance change comparisons are provided in Fig. S13.
