Lala A K, Kaul P
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Bombay.
J Biol Chem. 1992 Oct 5;267(28):19914-8.
The involvement of molten globule state as a distinct intermediate in the denaturation process in proteins is well documented. However, the structural characterization of such an intermediate is far from complete. We have, using fluorescence and fluorescence quenching, studied the molten globule state of bovine alpha-lactalbumin. Unlike the native state, where all the 4 tryptophans are buried in the protein, 2 tryptophans are exposed in the molten globule state. Using the hydrophobic photoactivable reagent [3H]diazofluorene, we observe an increased hydrophobic exposure in the molten globule state. These structural characteristics conform to the current views on the molten globule state, i.e. it has similar secondary structure but a poorly defined tertiary structure. Our fluorescence studies indicate the involvement of a premolten globule state in the native to molten globule state transition. This premolten globule state exists at pH 5.0 and has a very compact structure involving increased hydrophobic interactions in the protein interior. These results are also supported by circular dichroism studies.
蛋白质变性过程中熔融球状态作为一种独特中间体的参与情况已有充分记录。然而，这种中间体的结构表征远未完成。我们利用荧光和荧光猝灭技术研究了牛α-乳白蛋白的熔融球状态。与天然态不同，在天然态中所有4个色氨酸都埋藏在蛋白质内部，而在熔融球状态中有2个色氨酸是暴露的。使用疏水性光活化试剂[3H]重氮芴，我们观察到在熔融球状态中疏水性暴露增加。这些结构特征符合当前关于熔融球状态的观点，即它具有相似的二级结构但三级结构不明确。我们的荧光研究表明在天然态到熔融球状态的转变过程中存在一种前熔融球状态。这种前熔融球状态存在于pH 5.0时，具有非常紧密的结构，涉及蛋白质内部疏水相互作用的增加。这些结果也得到了圆二色性研究的支持。
