Zhou B, Tian K, Jing G
National Laboratory of Biomacromolecules, Institute of Biophysics, Academia Sinica, Beijing 100101, People's Republic of China.
Protein Eng. 2000 Jan;13(1):35-9. doi: 10.1093/protein/13.1.35.
Although molten globules have been widely accepted as a general intermediate in protein folding, there is no clear evidence to show their presence during nascent peptide folding. This paper concentrates on whether the molten globule state occurs, and if it does, when does it form during nascent peptide folding, by comparing the changes in conformation during peptide chain extension of staphylococcal nuclease R. The results show that a large N-terminal fragment of staphylococcal nuclease, SNR121, which already contains more than 80% amino acid sequence of the nuclease, is found to fulfill all the criteria for the molten globule state, suggesting that the molten globule should occur at a later stage of peptide elongation. At this stage the hydrophobic collapse of the polypeptide chain occurs driven by the hydrophobic force, which leads to the formation of a solvent-accessible non-polar core, characterized by the high ANS-binding fluorescence. The nascent peptide folding of the nuclease is a hierarchical process that at the very least includes the following steps: secondary structure accumulation, pre-molten globule state, molten globule state, post-molten globule state and finally the native state. Constant conformation adjustment is necessary for correct folding and active expression of the protein.
尽管熔球态已被广泛认为是蛋白质折叠过程中的一种普遍中间体，但尚无明确证据表明其在新生肽折叠过程中存在。本文通过比较葡萄球菌核酸酶R肽链延伸过程中的构象变化，着重研究熔球态是否会出现，以及如果出现，在新生肽折叠过程中何时形成。结果表明，葡萄球菌核酸酶的一个大的N端片段SNR121，其氨基酸序列已超过核酸酶的80%，被发现符合熔球态的所有标准，这表明熔球态应出现在肽链延伸的后期。在此阶段，多肽链在疏水力的驱动下发生疏水塌缩，导致形成一个可被溶剂接触的非极性核心，其特征是具有高ANS结合荧光。核酸酶的新生肽折叠是一个分级过程，至少包括以下步骤：二级结构积累、前熔球态、熔球态、后熔球态，最终形成天然态。蛋白质的正确折叠和活性表达需要不断的构象调整。
