Figure 5.

Fit of the characteristic saw-tooth pattern obtained by the unzipping of the hexameric HPI protein complex (Fig. 4B). Each monomer is connected to its neighbor by a polypeptide whose extended length is 7.3 nm on average (Fig. 4F). Peaks can be fitted by using the worm-like chain equation: F(x) = (kT/b)[0.25(1 − x/L)⁻² − 0.25 + x/L], taking a persistence length b = 0.4 nm. F represents the force, k the Boltzmann constant, T the absolute temperature, b the persistence length of the polypeptide chain, x the extension, and L the contour length of the polypeptide chain. This behavior compares favorably to the force-extension curves of titin molecules (10).