Structure-relaxation mechanism for the response of T4 lysozyme cavity mutants to hydrostatic pressure.
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.
Jules Stein Eye Institute, University of California, Los Angeles, CA 90095; and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095.
Michael T
MT
Lerch
Jules Stein Eye Institute, University of California, Los Angeles, CA 90095; and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095.
Carlos J
CJ
López
Jules Stein Eye Institute, University of California, Los Angeles, CA 90095; and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095.
Zhongyu
Z
Yang
Jules Stein Eye Institute, University of California, Los Angeles, CA 90095; and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095.
Margaux J
MJ
Kreitman
Jules Stein Eye Institute, University of California, Los Angeles, CA 90095; and.
Joseph
J
Horwitz
Jules Stein Eye Institute, University of California, Los Angeles, CA 90095; and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095 hubbellw@jsei.ucla.edu.
Wayne L
WL
Hubbell
D017122:Bacteriophage T4 / Q000201:enzymology*; D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D006874:Hydrostatic Pressure; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry* / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012997:Solvents; D013329:Structure-Activity Relationship; D013696:Temperature; D013816:Thermodynamics
D008024:Ligands; D012997:Solvents; D009113:Muramidase
DEER; EPR; conformational exchange; protein structural dynamics