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The three states of globular proteins: Acid denaturation
Author(s) -
Alonso Darwin O. V.,
Dill Ken A.,
Stigter Dirk
Publication year - 1991
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360311317
Subject(s) - chemistry , globular protein , crystallography , myoglobin , native state , enthalpy , phase diagram , denaturation (fissile materials) , calorimetry , ionic strength , hydrophobic effect , thermodynamics , protein folding , lysozyme , ionic bonding , phase (matter) , aqueous solution , organic chemistry , ion , biochemistry , physics , nuclear chemistry
We describe statistical mechanical theory that aims to predict protein stabilities as a function of temperature, pH, and salt concentration, from the physical properties of the constituent amino acids: (1) the number of nonpolar groups, (2) the chain length, (3) the temperature‐dependent free energy of transfer, (4) the pKa's (including those in the native state) and their temperature dependencies. We calculate here the phase diagrams for apomyoglobin and hypothetical variant proteins. The theory captures essential features of protein stability including myoglobin's T m vs pH as measured by P. L. Privalov [(1979) Advances in Protein Chemistry , Vol. 33, pp. 167–241] and its ionic strength vs pH phase diagram as measured by Y. Goto and A. L. Fink [(1990) Journal of Molecular Biology , Vol. 214, pp. 803–805]. The main predictions here are the following: (1) There are three stable states, corresponding to native (N), compact denatured (C), and highly unfolded (U), with transitions between them. (2) In agreement with experiments, the compact denatured state is predicted to have enthalpy closer to U than N because even though there is considerable hydrophobic “clustering” in C, this nevertheless represents a major loss of hydrophobic contacts relative to configurations (N) that have a hydrophobic “core.” (3) C becomes more prominent in the phase diagram with increasing nonpolar content or decreasing chain length, perhaps thus accounting for (a) why lysozyme and α‐lactalbumin differ in their denatured states, and (b) why shortened Staph nuclease molecules are compact. (4) Of major importance for protein calorimetry is Privalov's observation that the enthalpy of folding, ΔH ( T , pH) is independent of pH. The theory accounts for this through the prediction that the main electrostatic contribution to stability is not enthalpic; the main contribution is the entropy, mainly due to the different distributions of protons and small ions in the native and denatured states.