Thermodynamic and Structural Properties of the Acid Molten Globule State of Horse Cytochrome c

Abstract

To understand the stabilization, folding, and functional mechanisms of proteins, it is very important to understand the structural and thermodynamic properties of the molten globule state. In this study, the global structure of the acid molten globule state, which we call MG1, of horse cytochrome c at low pH and high salt concentrations was evaluated by solution X-ray scattering (SXS), dynamic light scattering, and circular dichroism measurements. MG1 was globular and slightly (3%) larger than the native state, N. Calorimetric methods, such as differential scanning calorimetry and isothermal acid-titration calorimetry, were used to evaluate the thermodynamic parameters in the transitions of N to MG1 and MG1 to denatured state D of horse cytochrome c. The heat capacity change, ΔC(p), in the N-to-MG1 transition was determined to be 2.56 kJ K(-1) mol(-1), indicating the increase in the level of hydration in the MG1 state. Moreover, the intermediate state on the thermal N-to-D transition of horse cytochrome c at pH 4 under low-salt conditions showed the same structural and thermodynamic properties of the MG1 state in both SXS and calorimetric measurements. The Gibbs free energy changes (ΔG) for the N-to-MG1 and N-to-D transitions at 15 °C were 10.9 and 42.2 kJ mol(-1), respectively.

Structural basis of urea-induced unfolding: Unraveling the folding pathway of hemochromatosis factor E

“…This is mainly because of sensitivity of different probes and also due to the difference in property that we measure with a particular type of probe. Similar results has been reported previously that one probe is able to detect intermediate state while no intermediate state is detected in the folding of the same protein under the same experimental condition if probe is different [68][69][70].…”

Structural transformations of cytochrome c upon interaction with cardiolipin

“…At low pH and high salt, the protein becomes a molten globule: a compact state with largely preserved secondary but fluctuating tertiary structure (Ohgushi and Wada, 1983; Jordan et al, 1995; Pletneva et al, 2005; Nakamura et al, 2011). Ligand substitution frequently accompanies conformational changes of cyt c .…”

Characterization of pre-molten globule state of yeast iso-1-cytochrome c and its deletants at pH 6.0 and 25 °C

“…Lastly, the hydrodynamic volume of A state determined by DLS measurements (Table 1) is approximately 1.5 times larger than that of the N state of respective proteins, fulfilling the last criterion of being a MG, namely, criterion (d) mentioned above [75]. Thus all pieces of structural evidence imply that A state of each deletant of WT y-cyt-c is a MG state as observed for other cyts-c [42,43,56,[76][77][78][79][80][81][82][83][84][85][86][87][88][89][90].…”