  Nonlinear effects in protein dynamics are expected to play role in function,
particularly of allosteric nature, by facilitating energy transfer between
vibrational modes. A recently proposed method focusing on the non-Gaussian
shape of the population near equilibrium projects this information onto real
space in order to identify the aminoacids relevant to function. We here apply
this method to three ancestral proteins in glucocorticoid receptor (GR) family
and show that the mutations that restrict functional activity during GR
evolution correlate significantly with locations that are highlighted by the
nonlinear contribution to the near-native configurational distribution. Our
findings demonstrate that nonlinear effects are not only indispensible for
understanding functionality in proteins, but they can also be harnessed into a
predictive tool for functional site determination.
