The interplay of turn formation and hydrophobic interactions on the early kinetic events in protein folding
The interplay of turn formation and hydrophobic interactions on the early kinetic events in protein folding
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DOI：
10.1039/c1cc13278d
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发表时间：
2012-01-14
影响因子：
4.9
通讯作者：
Chan, Sunney I.
中科院分区：
文献类型：
--
作者：
Huang, Joseph Jen-Tse;Larsen, Randy W.;Chan, Sunney I.
虽然转角形成和疏水相互作用在蛋白质折叠的启动中起主导作用，但它们对折叠动力学和蛋白质结构稳定性的各自贡献仍然知之甚少。在这里，我们应用了一个光不稳定的连接子来“笼住”声音重要的结构基序，包括α-螺旋和β-折叠，进入它们的非天然状态。然后，通过激光闪光光解及其重折叠事件，然后进行光声量热法 (PAC) 和光热束偏转 (PBD)，使这些“笼状”结构基序松弛。这些实验与我们之前的结果相结合表明，如果该过程仅由转角形成和随后的螺旋传播驱动，则自发的α螺旋形成可以极其迅速地发生（10（8）-10（9）s（-1））。然而，如果疏水性氨基酸残基侧链的隔离参与重折叠过程，这可能提供超出仅由转角形成提供的额外驱动力，则重折叠速率将被延迟，通常延迟多个数量级。这通常是三链β-折叠 (10(7)-10(8) s(-1)) 和 β-发夹 (10(5)-10(6) s(-1)) 形成的情况。因此，我们提出蛋白质利用与转角形成、疏水相互作用或三级结构整体塌陷相关的时间尺度层次以有序的方式完成折叠过程，因为这些事件在时间上充分分离并且不会相互干扰。
While both turn formation and hydrophobic interactions play dominant roles in the initiation of protein folding, their individual contributions to the folding kinetics and to the structural stability of the protein still remain poorly understood. Here, we applied a photolabile linker to "cage" sonic important structural motifs, including both alpha-helices and beta-sheets, into their non-native states. These "caged" structural motifs are then relaxed by laser-flash photolysis and their refolding events followed by photoacoustic calorimetry (PAC) and photothermal beam deflection (PBD). These experiments, combined with our previous results, revealed that spontaneous alpha-helix formation can occur extremely rapidly (10(8)-10(9) s(-1)) if the process is driven solely by turn formation followed by helix propagation. However, if sequestering of the side chains of hydrophobic amino acid residues participates in the refolding process, which may provide additional driving force beyond that afforded by turn formation alone, the refolding rate will be retarded, often by many orders of magnitude. This is usually the case in the formation of three-stranded beta-sheets (10(7)-10(8) s(-1)) and beta-hairpins (10(5)-10(6) s(-1)). Thus, we propose that proteins take advantage of the hierarchy of timescales associated with either turn formation, hydrophobic interactions, or global collapse of tertiary structure to accomplish the folding process in an orderly fashion, as these events are sufficiently separated in time and do not interfere with one another.