The native state conformational heterogeneity in the energy landscape of protein folding.

The native structure of proteins is central to various functions performed by cells. A vital part of the structure-function paradigm of proteins is their inherent flexibility and dynamics. The dynamic interconversion between the conformational substates in the heterogeneous native state basin of the energy landscape enables a single protein molecule to perform multiple functions. The dynamics among the substates are assisted by the motion of different structural elements of a protein out of which side-chains of amino acids hold a significant position due to their involvement in various functions such as molecular recognition and dynamic allostery. This review briefly describes the origin of conformational heterogeneity in the native state ensemble and the motions of different structural modules that assist the equilibrium dynamics of the conformational substates. The review then centers the discussion on conformational heterogeneity due to side-chain movements in proteins, the experimental methods to detect and characterize them and their role in performing multiple functions.