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The pressure-temperature phase diagram of hen lysozyme at low pH

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ABSTRACT

The equilibrium unfolding of hen lysozyme at pH 2 was studied as a function of pressure (0.1~700MPa) and temperature (−10°C~50°C) using Trp fluorescence as monitor supplemented by variable pressure 1H NMR spectroscopy (0.1~400MPa). The unfolding profiles monitored by the two methods allowed the two-state equilibrium analysis between the folded (N) and unfolded (U) conformers. The free energy differences ΔG (=GU–GN) were evaluated from changes in the wavelength of maximum fluorescence intensity (λmax) as a function of pressure and temperature. The dependence of ΔG on temperature exhibits concave curvatures against temperature, showing positive heat capacity changes (ΔCp=CpU–CpN= 1.8–1.9 kJ mol−1 deg−1) at all pressures studied (250~400 MPa), while the temperature TS for maximal ΔG increased from about 10°C at 250MPa to about 40°C at 550MPa. The dependence of ΔG on pressure gave negative volume changes (ΔV=VU–VN) upon unfolding at all temperatures studied (−86~−17 mlmol−1 for −10°C~50°C), which increase significantly with increasing temperature, giving a positive expansivity change (Δα~1.07mlmol−1 deg−1). A phase-diagram between N and U (for ΔG=0) is drawn of hen lysozyme at pH 2 on the pressure-temperature plane. Finally, a three-dimensional free energy landscape (ΔG) is presented on the p-T plane.

No MeSH data available.


Three-dimensional free-energy landscape of hen lysozyme at pH 2 in the range of pressure from 250MPa to 550MPa and temperature from 200 K to 380 K, drawn as overlay of eq. 5 at various pressures.
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f7-5_1: Three-dimensional free-energy landscape of hen lysozyme at pH 2 in the range of pressure from 250MPa to 550MPa and temperature from 200 K to 380 K, drawn as overlay of eq. 5 at various pressures.

Mentions: In Figure 7, we draw the energy landscape of hen lysozyme at low pH on pressure and temperature axes based on eq. 5 on the approximation of isothermal compressibility change Δκ within the pressure range studied. This will provide the basis for studying hen lysozyme at low pH by varying temperature and/or pressure.


The pressure-temperature phase diagram of hen lysozyme at low pH
Three-dimensional free-energy landscape of hen lysozyme at pH 2 in the range of pressure from 250MPa to 550MPa and temperature from 200 K to 380 K, drawn as overlay of eq. 5 at various pressures.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036640&req=5

f7-5_1: Three-dimensional free-energy landscape of hen lysozyme at pH 2 in the range of pressure from 250MPa to 550MPa and temperature from 200 K to 380 K, drawn as overlay of eq. 5 at various pressures.
Mentions: In Figure 7, we draw the energy landscape of hen lysozyme at low pH on pressure and temperature axes based on eq. 5 on the approximation of isothermal compressibility change Δκ within the pressure range studied. This will provide the basis for studying hen lysozyme at low pH by varying temperature and/or pressure.

View Article: PubMed Central - PubMed

ABSTRACT

The equilibrium unfolding of hen lysozyme at pH 2 was studied as a function of pressure (0.1~700MPa) and temperature (−10°C~50°C) using Trp fluorescence as monitor supplemented by variable pressure 1H NMR spectroscopy (0.1~400MPa). The unfolding profiles monitored by the two methods allowed the two-state equilibrium analysis between the folded (N) and unfolded (U) conformers. The free energy differences ΔG (=GU–GN) were evaluated from changes in the wavelength of maximum fluorescence intensity (λmax) as a function of pressure and temperature. The dependence of ΔG on temperature exhibits concave curvatures against temperature, showing positive heat capacity changes (ΔCp=CpU–CpN= 1.8–1.9 kJ mol−1 deg−1) at all pressures studied (250~400 MPa), while the temperature TS for maximal ΔG increased from about 10°C at 250MPa to about 40°C at 550MPa. The dependence of ΔG on pressure gave negative volume changes (ΔV=VU–VN) upon unfolding at all temperatures studied (−86~−17 mlmol−1 for −10°C~50°C), which increase significantly with increasing temperature, giving a positive expansivity change (Δα~1.07mlmol−1 deg−1). A phase-diagram between N and U (for ΔG=0) is drawn of hen lysozyme at pH 2 on the pressure-temperature plane. Finally, a three-dimensional free energy landscape (ΔG) is presented on the p-T plane.

No MeSH data available.