Experimental studies show that many proteins fold along sequential pathways defined by folding intermediates. An intermediate may not always be a single population of molecules but may consist of subpopulations that differ in their average structure. These subpopulations are likely to fold via independent pathways. Parallel folding and unfolding pathways appear to arise because of structural heterogeneity. For some proteins, the folding pathways can effectively switch either because different subpopulations of an intermediate get populated under different folding conditions, or because intermediates on otherwise hidden pathways get stabilized, leading to their utilization becoming discernible, or because mutations stabilize different substructures. Therefore, the same protein may fold via different pathways in different folding conditions. Multiple folding pathways make folding robust, and evolution is likely to have selected for this robustness to ensure that a protein will fold under the varying conditions prevalent in different cellular contexts.

中文翻译：

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蛋白质折叠中的多种途径和结构异质性。

实验研究表明，许多蛋白质沿着由折叠中间体定义的顺序途径折叠。中间体可能并不总是单一的分子种群，而是可能包含平均结构不同的亚群。这些亚群可能会通过独立途径折叠。由于结构异质性，似乎出现了平行的折叠和展开路径。对于某些蛋白质，折叠路径可以有效地转换，这是因为中间体的不同亚群在不同的折叠条件下被填充，或者因为隐藏路径上的中间体被稳定化，导致其利用变得可辨别，或者因为突变稳定了不同的亚结构。因此，相同的蛋白质可能在不同的折叠条件下通过不同的途径折叠。