UCSF

Altered states: in search of 'hidden' protein structuresX-ray crystallography and NMR spectroscopy are two powerful tools used by structural biologists to determine the three-dimensional structures and characterize the dynamic properties of proteins. In this paper, the authors used both of these methods to identify and characterize a 'hidden' high-energy substate of human cyclophilin A, a proline isomerase. This was made possible by engineering a modified form of the enzyme incorporating a mutation at a distance from the active site that could stabilize this previously hidden conformation by inverting the equilibrium between the various substates and reducing the conformational interconversion rates and the catalytic rate. This approach should be broadly applicable to many other proteins and could lead to the reinterpretation of crystal structures determined previously.