Critical buckling length versus persistence length: what governs biofilament conformation?

We numerically study the length dependence in the bending stiffness of alpha helices, coiled coils, and a linear chain model. As the length approaches what we named the critical buckling length lc, the chain appears to become increasingly more flexible. This is due to weak nonbonded attractions that eventually lead to buckling instability and alter the chain's conformational ensemble. For alpha helices and coiled coils, lc is much less than their respective persistence lengths, so lc is the defining length scale for their conformations. These results elucidate the importance of weak nonspecific attractions that are inherent in many biofilaments in physiological conditions.