Protein Stability

Abstract

Abstract Proteins must fold to a globular conformation to carry out the most important tasks in living organisms. The folded, biologically active conformation of a protein is only marginally more stable than the unfolded, inactive conformations. Thus, making proteins more stable is important in medicine and basic research. The major destabilising force that must be overcome is conformational entropy. The major stabilising forces are the hydrophobic effect and hydrogen bonding. The ionisable side chains of amino acid residues may also contribute favourably to protein stability through attractive charge–charge interactions, ion pair formation or the formation of hydrogen bonds when such groups are buried in the protein interior. Replacing a nonproline or nonglycine residue in a β‐turn can also significantly increase protein stability. Key Concepts: Under physiological conditions, a folded protein is ∼20 to 60 kJ mol –1 more stable than unfolded forms. The major destabilising force to protein folding is conformational entropy, which contributes ∼7 kJ mol −1 per residue. The major stabilising forces are the hydrophobic effect, where the burying of each –CH 2 – contributes ∼−5 kJ mol −1 , and hydrogen bonding, especially buried intramolecular hydrogen bonds, which may contribute ∼−7 kJ mol −1 per bond. The ionisable side chains of amino acid residues may contribute favourably to protein stability through attractive charge–charge interactions, ion pair formation and hydrogen bonding when the ionisable group is buried in the protein interior. Replacing a nonproline or nonglycine residue in a β‐turn may increase protein stability.