Exploring the complexity of the free energy landscape of protein folding

Proteins have dynamic structures that undergo chain motions on timescales spanning picoseconds to seconds. Resolving the resultant complexity of the free energy landscape of protein conformations is essential for gaining an accurate insight into fundamental mechanistic aspects of the protein folding reaction. The use of high-resolution structural probes, sensitive to population distributions, has begun to enable the resolution of site-specific conformational heterogeneity at different stages of folding reaction. Different states populated during protein folding, including the unfolded state, collapsed intermediate states, and even the native state are found to possess significant conformational heterogeneity. Multiple folding pathways are likely to represent distinct sequences of structure formation. An insight into the nature of the energy barriers separating different conformational states populated during (un)folding can also be obtained by resolving heterogeneity.