  We provide evidence that the energy landscapes of folded proteins do not
shift with temperature, but the onset of functional dynamics is associated with
its effective sampling. The motion of the backbone is described by three
distinct regimes. One is associated with slow time scales of the activity along
the envelope of the energy surface defining the folded protein. Another, with
fast time scales, is due to activity along the pockets decorating the
folded-state envelope. The intermediate regime emerges at temperatures where
jumps between the pockets become possible, leading to an active protein.
