Three-state denaturation of α-lactalbumin by guanidine hydrochloride
Three-state denaturation of α-lactalbumin by guanidine hydrochloride
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盐酸胍对α-乳清蛋白的三态变性
DOI：
10.1016/0022-2836(76)90091-7
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发表时间：
1976
影响因子：
5.6
通讯作者：
S. Sugai
中科院分区：
文献类型：
--
作者：
K. Kuwajima;K. Nitta;M. Yoneyama;S. Sugai
本文用紫外圆二色性研究了α-乳清蛋白在盐酸胍作用下的可逆去折叠。从远紫外波长（222 nm）和近紫外波长（270 nm和296 nm）处的椭圆率变化获得的表观转变曲线的不一致性表明在变性过程中存在至少一种中间体。在270 nm和296 nm处对科顿效应有贡献的芳香残基似乎在两阶段过程的第一阶段中暴露于溶剂，而多肽链的螺旋区域似乎在第二阶段中被破坏。早期的工作已经证明了α-乳清蛋白的两种致密形式（天然（中性pH）形式和酸性形式）之间的酸转变。这里提出的结果表明，酸的形式产生的中间体在第一阶段的总展开在中性pH值。溶菌酶和α-乳白蛋白是已知的具有相似的一级结构，并预计具有相似的三级结构，但在其性质的几个差异已被描述。α-乳清蛋白和溶菌酶的去折叠转变的比较提供了与类似的三级结构相容的结果，尽管α-乳清蛋白的天然状态的稳定化自由能比溶菌酶小3至5 kcal/mol。展开反应的pH依赖性可以用异常组氨酰和羧基残基来描述。变性过程中稳定中间体的存在可能导致两种蛋白质在天然状态下的动力学特征差异，从而为它们已知的化学反应性差异提供合理的解释。
The reversible unfolding of α-lactalbumin by guanidine hydrochloride has been studied at 25.0 °C by means of ultraviolet circular dichroism measurements. The non-coincidence of the apparent transition curves obtained from the ellipticity changes at far (222 nm) and at near (270 nm and 296 nm) ultraviolet wave-lengths demonstrates the presence of at least one intermediate in the denaturation process. The aromatic residues which contribute to the Cotton effects at 270 nm and at 296 nm appear to be exposed to solvent in the first stage of a two-stage process, while the helical regions of the polypeptide chain appear to be destroyed in the second stage. Earlier work has demonstrated an acid transition between two compact forms of α-lactalbumin, a native (neutral pH) form and an acid form. Results presented here suggest that the acid form is produced as an intermediate in the first stage of total unfolding at neutral pH.Lysozyme and α-lactalbumin are known to have similar primary structures and are expected to have similar tertiary structures, but several differences in their properties have been described. The comparison of the unfolding transitions of α-lactalbumin and lysozyme provides a result compatible with similar tertiary structures, although the free energy of stabilization of the native state is 3 to 5 kcal/mol smaller for α-lactalbumin than for lysozyme. The pH dependence of the unfolding reaction can be described in terms of abnormal histidyl and carboxyl residues. The presence of a stable intermediate in the denaturation process may cause a difference in dynamic character in the native state between the two proteins and thus provide a reasonable interpretation for their known differences in chemical reactivity.