An autonomous folding unit mediates the assembly of two-stranded coiled coils

Subunit oligomerization of many proteins is mediated by coiled-coil domains. Although the basic features contributing to the thermodynamic stability of coiled coils are well understood, the mechanistic details of their assembly have not yet been dissected. Here we report a 13-residue sequence pattern that occurs with limited sequence variations in many two-stranded coiled coils and that is absolutely required for the assembly of the Dictyostelium discoideum actin-bundling protein cortexillin I and the yeast transcriptional activator GCN4. The functional relationship between coiled-coil “trigger” sequences was manifested by replacing the intrinsic trigger motif of GCN4 with the related sequence from cortexillin I. We demonstrate that these trigger sequences represent autonomous helical folding units that, in contrast to arbitrarily chosen heptad repeats, can mediate coiled-coil formation. Aside from being of general interest for protein folding, trigger motifs should be of particular importance in the protein de novo design.

许多蛋白质的亚基寡聚化过程由卷曲螺旋结构域（coiled-coil domains）介导。尽管卷曲螺旋热力学稳定性的核心特征已被充分阐明，但其组装的机制细节仍未被完全解析。本文报道了一种在众多两股卷曲螺旋结构中出现、且仅存在有限序列变异的13残基序列模体，该模体是盘基网柄菌（Dictyostelium discoideum）肌动蛋白束蛋白cortexillin I与酵母转录激活因子GCN4进行组装所绝对必需的关键元件。通过将GCN4的固有触发基序替换为来自cortexillin I的同源序列，我们验证了这类卷曲螺旋「触发」序列之间的功能相关性。实验证实，这类触发序列属于自主螺旋折叠单元：与任意选取的七肽重复序列（heptad repeats）不同，它们可有效介导卷曲螺旋的形成。除了对蛋白质折叠研究具有普遍的学术意义外，这类触发基序在蛋白质从头设计中也具有尤为重要的应用价值。