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# Denaturant mediated unfolding of both native and molten globule states of maltose binding protein are accompanied by large $\Delta Cp^'s$

Sheshadri, S and Lingaraju, GM and Varadarajan, R (1999) Denaturant mediated unfolding of both native and molten globule states of maltose binding protein are accompanied by large $\Delta Cp^'s$. In: Protein Science, 8 (8). pp. 1689-1695.

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## Abstract

Maltose binding protein (MBP) is a large, monomeric two domain protein containing 370 amino acids. In the absence of denaturant at neutral pH, the protein is in the native state, while at pH 3.0 it forms a molten globule. The molten globule lacks a tertiary circular dichroism signal but has secondary structure similar to that of the native state. The molten globule binds 8-anilino-1-naphthalene sulfonate (ANS). The unfolding thermodynamics of MBP at both pHs were measured by carrying out a series of isothermal urea melts at temperatures ranging from 274-329 K. At 298 K, values of $\Delta G^o$ , $\Delta C_p$, and $C_m$ were $3.1\pm 0.2 \hspace{2mm} kcal \hspace{2mm} mol^{-1}$, $5.9\pm 0.8 \hspace{2mm} kcal \hspace{2mm} mol^{-1} K^{-1}$ $(15.9 \hspace{2mm} cal\hspace{2mm} (mol-residue)^{-1} K^{-1})$, and 0.8 M, respectively, at pH 3.0 and $14.5\pm 0.4 \hspace{2mm} kcal\hspace{2mm} mol^{-1}$, $8.3\pm 0.7 \hspace{2mm} kcal \hspace{2mm} mol^{-1} K^{-1}$ $(22.4 \hspace{2mm} kcal (mol-residue)^{-1} K^{-1})$, and 3.3 M, respectively, at pH 7.1. Guanidine hydrochloride denaturation at pH 7.1 gave values of $\Delta G^o$ and $\Delta C_p$ similar to those obtained with urea. The m values for denaturation are strongly temperature dependent, in contrast to what has been previously observed for small globular proteins. The value of $\Delta C_p$ per mol-residue for the molten globule is comparable to corresponding values of $\Delta C_p$ for the unfolding of typical globular proteins and suggests that it is a highly ordered structure, unlike molten globules of many small proteins. The value of $\Delta C_p$ per mol-residue for the unfolding of the native state is among the highest currently known for any protein.

Item Type: Journal Article Copyright of this article belongs to The Protein Society. Heat capacity;Molten globule;Protein stability Division of Biological Sciences > Molecular Biophysics Unit 17 Oct 2007 19 Sep 2010 04:40 http://eprints.iisc.ernet.in/id/eprint/12146

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