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Structure-relaxation mechanism for the response of T4 lysozyme cavity mutants to hydrostatic pressure. Proc Natl Acad Sci U S A 2015 May 12;112(19):E2437-46 PMID: 25918400 PMCID: PMC4434698

Abstract

Application of hydrostatic pressure shifts protein conformational equilibria in a direction to reduce the volume of the system. A current view is that the volume reduction is dominated by elimination of voids or cavities in the protein interior via cavity hydration, although an alternative mechanism wherein cavities are filled with protein side chains resulting from a structure relaxation has been suggested [López CJ, Yang Z, Altenbach C, Hubbell WL (2013) Proc Natl Acad Sci USA 110(46):E4306-E4315]. In the present study, mechanisms for elimination of cavities under high pressure are investigated in the L99A cavity mutant of T4 lysozyme and derivatives thereof using site-directed spin labeling, pressure-resolved double electron-electron resonance, and high-pressure circular dichroism spectroscopy. In the L99A mutant, the ground state is in equilibrium with an excited state of only ∼ 3% of the population in which the cavity is filled by a protein side chain [Bouvignies et al. (2011) Nature 477(7362):111-114]. The results of the present study show that in L99A the native ground state is the dominant conformation to pressures of 3 kbar, with cavity hydration apparently taking place in the range of 2-3 kbar. However, in the presence of additional mutations that lower the free energy of the excited state, pressure strongly populates the excited state, thereby eliminating the cavity with a native side chain rather than solvent. Thus, both cavity hydration and structure relaxation are mechanisms for cavity elimination under pressure, and which is dominant is determined by details of the energy landscape.

Author List

Lerch MT, López CJ, Yang Z, Kreitman MJ, Horwitz J, Hubbell WL

Author

Michael Lerch PhD Assistant Professor in the Biophysics department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Bacteriophage T4
Circular Dichroism
Electron Spin Resonance Spectroscopy
Hydrogen-Ion Concentration
Hydrostatic Pressure
Ligands
Magnetic Resonance Spectroscopy
Models, Molecular
Muramidase
Mutagenesis, Site-Directed
Mutation
Protein Denaturation
Protein Folding
Protein Structure, Secondary
Solvents
Structure-Activity Relationship
Temperature
Thermodynamics



View this publication's entry at the Pubmed website PMID: 25918400
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