Optimal flexibility for conformational transitions in macromolecules

Conformational transitions in macromolecular complexes often
involve the reorientation of leverlike structures. Using a simple
theoretical model, we show that the rate of such transitions is
drastically enhanced if the lever is bendable, e. g., at a
localized hinge. Surprisingly, the transition is fastest with an
intermediate flexibility of the hinge. In this intermediate regime,
the transition rate is also least sensitive to the amount of
"cargo" attached to the lever arm, which could be exploited by
molecular motors. To explain this effect, we generalize the
Kramers-Langer theory for multidimensional barrier crossing to
configuration-dependent mobility matrices.