Principles of Protein Stability. Part 1—Reversible Unfolding of Proteins: Kinetic and Thermodynamic Analysis

Over 30 years ago Anfinsen and his colleagues demonstrated that the amino acid sequence is the primary determinant of the three-dimensional structure of a folded protein (1). This seminal observation stimulated numerous efforts to define the rules that govern the folding reaction (2–6). Unfortunately, little progress on solving the folding code has been made until recently. The main obstacle has been the high co-operativity of the unfolding transition. Only the native and unfolded forms are highly populated under equilibrium conditions; stable, partially folded forms are generally not detected. Transient intermediates, when they do appear, typically have lifetimes in the millisecond range, making it difficult to characterize their structures.