Hierarchical unfolding of the α-lactalbumin molten globule:: Presence of a compact intermediate without a unique tertiary fold

被引:16
作者
Chakraborty, S [1 ]
Pang, ZY [1 ]
机构
[1] Univ Connecticut, Ctr Hlth, Dept Biochem, Farmington, CT 06030 USA
关键词
alpha-lactalbumin; molten globule; circular dichroism; disulfide exchange; protein folding;
D O I
10.1006/jmbi.2000.3660
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The difference between the framework model and the hydrophobic collapse model of protein folding largely rests on whether a secondary-structure framework can exist independently of native tertiary interactions. Here, we used circular dichroism and disulfide exchange experiments to examine the unfolding mechanism of alpha-LA(alpha), a two-disulfide variant of human alpha-lactalbumin (alpha-LA) that adopts a molten globule conformation under near physiological conditions. Our results show that as the concentration of denaturant increases, the alpha-LA molten globule first loses its ability to form a specific, native-like tertiary fold. Subsequently, at a higher denaturant concentration, the protein loses its secondary structure and adopts an extended conformation. A compact, non-native disulfide bond isomer, which does not form significantly under both native and strongly denaturing conditions, was found to be moderately populated in similar to 2 M guanidine hydrochloride (GuHCl). Qualitatively the same result was also obtained in urea. These results suggest that formation of secondary structure is a necessary, but not sufficient condition for formation of the native-like tertiary fold and support a hierarchical model of protein folding. (C) 2000 Academic Press.
引用
收藏
页码:1 / 6
页数:6
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