Free Energy of Burying Hydrophobic Residues in the Interface between Protein Subunits

• Published in: Proceedings of the National Academy of Sciences - PNAS 1998-05, Vol.95 (11), p.6103-6107
• Main Authors: Vallone, Beatrice, Miele, Adriana E., Vecchini, Paola, Chiancone, Emilia, Brunori, Maurizio
• Format: Article
• Language: English
• Subjects: Allosteric Regulation; Amino acids; Animals; Atoms; Biological Sciences; Correlations; Cost estimates; Dimers; Energy; Energy Transfer; Free energy; Hemoglobins - chemistry; Hemoglobins - genetics; Hemoglobins - metabolism; Humans; Mutation; Physics; Protein Binding; Protein subunits; Proteins; Solvation; Solvents; Surface areas; Thermodynamics
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.95.11.6103

We have obtained an experimental estimate of the free energy change associated with variations at the interface between protein subunits, a subject that has raised considerable interest since the concept of accessible surface area was introduced by Lee and Richards [Lee, B. & Richards, F. M. (1971) J. Mol. Biol. 55, 379-400]. We determined by analytical ultracentrifugation the dimer-tetramer equilibrium constant of five single and three double mutants of human Hb. One mutation is at the stationary α1β1interface, and all of the others are at the sliding α1β2interface where cleavage of the tetramer into dimers and ligand-linked allosteric changes are known to occur. A surprisingly good linear correlation between the change in the free energy of association of the mutants and the change in buried hydrophobic surface area was obtained, after corrections for the energetic cost of losing steric complementarity at the α β dimer interface. The slope yields an interface stabilization free energy of -15 ± 1.2 cal/mol upon burial of 1 angstrom2of hydrophobic surface, in very good agreement with the theoretical estimate given by Eisenberg and McLachlan [Eisenberg, D. & McLachlan, A. D. (1986) Nature (London) 319, 199-203].