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Axial and Radial Forces of Cross-Bridges Depend on Lattice Spacing

Figure 3

Energy and kinetics of the multi-spring cross-bridge models change with axial offset and lattice spacing.

Axial offset is the distance between the current axial location of the cross-bridge tip and the location where the cross-bridge attaches to the thick filament. Lattice spacing () is defined as in Millman (1998) [3], with an offset to account for filament thicknesses so the cross-bridge spans the filaments at a rest lattice spacing of 34 nm. (A)–(H) The properties of the 4sXB model (A, C, E, and G) and the 2sXB model (B, D, F, and H) as they change with binding site offset and lattice spacing. (A) depicts the free energy of the 4sXB model at various lattice spacings, with the head stretched to an axial offset from the thick filament attachment point. The free energy of the 2sXB model is shown in (B). (C) and (D) show , the probability that the 4sXB and 2sXB models will transition from an unbound state to a bound state. (E) and (F) show , the probability of transition from a pre-power stroke state to a post-power stroke state, for the same cross-bridges, axes, and scales as (C) and (D) show . (G) and (H) show , the probability of unbinding from a post-power stroke state. The reverse rate constants, , , and are back-calculated from the forward rate constants.

doi: https://doi.org/10.1371/journal.pcbi.1001018.g003