A long-standing problem in molecular biology is the determination of a complete functional conformational landscape of proteins. This includes not only proteins' native structures, but also all their respective functional states, including functionally important intermediates. Here, we reveal a signature of functionally important states in several protein families, using direct coupling analysis, which detects residue pair coevolution of protein sequence composition. This signature is exploited in a protein structure-based model to uncover conformational diversity, including hidden functional configurations. We uncovered, with high resolution (mean ∼1.9 Å rmsd for nonapo structures), different functional structural states for medium to large proteins (200-450 aa) belonging to several distinct families. The combination of direct coupling analysis and the structure-based model also predicts several intermediates or hidden states that are of functional importance. This enhanced sampling is broadly applicable and has direct implications in protein structure determination and the design of ligands or drugs to trap intermediate states.A s demonstrated by Anfinsen in 1973 (1) for small and intermediate-size proteins, amino acid sequences contain all of the necessary information to determine their native structure and function. In principle, a complete physical understanding of all molecular interactions should be sufficient to uncover not only the proteins' native structures, but also all their respective functional states, including functionally important intermediates. This landscape is required for a complete knowledge of functional mechanisms and therefore it has implications for drug discovery. Advances in computational approaches have been promising in sampling such conformational intermediates (2, 3). However, in general, computational methods are limited by uncertainties in protein models as well as insufficient computational resources to achieve proper sampling. Experimental techniques such as crystallography or NMR spectroscopy have been successful in identifying functional protein structures but only for a fraction of the complete set of known protein sequences (4, 5). Additionally, the determination of functionally important intermediate states using such methods has been challenging due to their transient nature. One idea to confront this challenge is to search for clues in genomic data (6-10). Functional states under conformational selection should leave a trace in the evolutionary history of proteins. Recent results inspired by this hypothesis have led to the development of the powerful "direct coupling analysis" (DCA), which was able to predict a large number of direct structural contacts between residues from sequences alone (11). Other useful methods have been developed to define coupling among residue pairs (12, 13). Others have also looked into correlated electrostatic mutations to study the evolution of protein topology toward minimized interaction frustration (14). Integrating the DCA-predicted co...