Protein Stability

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 –CH2– 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.

Keywords: protein stability; conformational entropy; hydrophobic effect; hydrogen bonding; protein ionisable groups; β‐turns

Figure 1.

(a) The folding of the globular protein ribonuclease Sa. ΔG for this reaction under physiological conditions is the conformational stability. The folded form was drawn using MOLSCRIPT (Kraulis, ) and the Protein Data Bank entry 1RGG. (b) Rotation around the bonds in a polypeptide chain (Stryer, ).

Figure 2.

(a) Scheme illustrating the formation of an intramolecular hydrogen bond, a hydrophobic bond and an ion pair in the folding of a protein. (b) Contributions to the free energy of folding of ribonuclease Sa at 25 °C and pH 7. Ribonuclease Sa contains 96 amino acids. The values for the conformational entropy, hydrophobic effect and hydrogen bonding are taken from experimental studies. Contributions from ion pair formation are relatively small and not shown in this figure.

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Further Reading

Baase WA, Liu L, Tronrud DE and Matthews BW (2010) Lessons from the lysozyme of phage T4. Protein Science 19: 631–641.

Fersht A (1998) Structure and Mechanism in Protein Science: A Guide to Enzyme Catalysis and Protein Folding. New York: WH Freeman.

Makhatadze GI and Privalov PL (1995) Energetics of protein structure. Advances in Protein Chemistry 47: 307–425.

Matthews BW (1993) Structural and genetic analysis of protein stability. Annual Review of Biochemistry 62: 139–260.

Pace CN, Hebert EJ, Shaw KL et al. (1998) Conformational stability and thermodynamics of folding of ribonucleases Sa, Sa2 and Sa3. Journal of Molecular Biology 279: 271–286.

Pace CN, Huyghues‐Despointes BMP, Fu H et al. (2010) Urea denatured state ensembles contain extensive secondary structure that is increased in hydrophobic proteins. Protein Science 19: 929–943.

Voet D, Voet JG and Pratt CW (2012) Fundamentals of Biochemistry, 4th edn. New York: Wiley.

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How to Cite close
Pace, C Nick, Grimsley, Gerald R, Scholtz, J Martin, and Shaw, Kevin L(Feb 2014) Protein Stability. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003002.pub3]