Exploring the folding energy landscape with pressure

The unique role of pressure in protein folding studies is emphasized. Variable-pressure NMR experiments carried out under equilibrium conditions give unique opportunities to explore the energy landscape for protein folding. Intermediate conformers that may appear transiently in the kinetic folding experiments may be stably trapped under pressure, allowing examination of their conformations in site-specific detail with modern NMR spectroscopy. The intimate relationship between the kinetic folding experiment and the equilibrium pressure experiment is described with examples from ubiquitin and hen lysozyme.