Hierarchical unfolding of the alpha-lactalbumin molten globule: presence of a compact intermediate without a unique tertiary fold.
Hierarchical unfolding of the alpha-lactalbumin molten globule: presence of a compact intermediate without a unique tertiary fold.
复制标题
α-乳清蛋白熔球的分层展开：存在紧凑的中间体，没有独特的三级折叠。
DOI：
10.1006/jmbi.2000.3660
复制
发表时间：
2000
影响因子：
5.6
通讯作者：
Peng,Z
中科院分区：
文献类型：
--
作者：
Chakraborty,S;Peng,Z
蛋白质折叠的框架模型和疏水塌陷模型之间的差异主要取决于二级结构框架是否可以独立于天然三级相互作用而存在。在这里，我们使用圆二色性和二硫键交换实验来研究α-LA（α）的解折叠机制，α-LA（α）是人α-乳清蛋白（α-LA）的两个二硫键变体，在接近生理条件下采用熔融球构象。我们的研究结果表明，随着变性剂浓度的增加，α-LA熔融球首先失去了形成特异性的、天然的三级折叠的能力。随后，在较高的变性剂浓度下，蛋白质失去其二级结构并采用延伸构象。一个紧凑的，非天然的二硫键异构体，它不会形成显着的天然和强变性条件下，被发现是适度的人口在102 M盐酸胍（GuHCl）。定性地，在尿素中也获得了相同的结果。这些结果表明，二级结构的形成是一个必要的，但不是充分的条件，形成天然的三级折叠，并支持蛋白质折叠的层次模型。
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 α-LA(α), a two-disulfide variant of human α-lactalbumin (α-LA) that adopts a molten globule conformation under near physiological conditions. Our results show that as the concentration of denaturant increases, the α-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 ∼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.