Thermodynamic stability of the molten globule states of apomyoglobin.


Abstract

Whereas horse apomyoglobin is fully unfolded at pH 2 in the absence of salt, addition of a salt such as sodium chloride or sodium trichloroacetate stabilizes the molten globule state. Thermal unfolding of the salt-stabilized molten globule states of horse apomyoglobin at pH 2 measured by far-UV circular dichroism occurs not only on heating (i.e. heat-denaturation) but also on cooling (i.e. cold-denaturation). This demonstrates that a hydrophobic interaction contributes to the stability of the molten globule state and suggests that the unfolding transition can be represented by a cooperative two-state mechanism. To clarify the mechanism of conformational transition, we investigated the thermal unfolding of the chloride-stabilized molten globule state by differential scanning calorimetry. We observed a broad but distinct excess heat capacity peak, which is consistent with the unfolding transition measured by circular dichroism. To further characterize the molten globule states, we examined by far-UV circular dichroism the denaturant-induced unfolding transitions of the molten globule states stabilized by sodium chloride or sodium trichloroacetate. The urea-induced unfolding transitions of the molten globule states were explained by the two-state mechanism. The guanidine-hydrochloride-induced unfolding experiments clarified that the trichloroacetate-stabilized molten globule state is distinct from the chloride-stabilized one and that the former involves additional helical segment(s). These results support a view that the thermal unfolding of the molten globule states at pH 2 can be approximated by a two-state transition. However, several results suggested that a combined mechanism incorporating the two-state transition and a gradual structural change would be more general in describing the conformational transition of the molten globule states. Study holds ProTherm entries: 7479, 7480, 7481, 7482, 7483, 7484 Extra Details: apomyoglobin; differential scanning calorimetry;,hydrophobic interactions; molten globule; protein folding

Submission Details

ID: chSb8C2n

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:34 p.m.

Version: 1

Publication Details
Nishii I;Kataoka M;Goto Y,J. Mol. Biol. (1995) Thermodynamic stability of the molten globule states of apomyoglobin. PMID:7608972
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