Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.
J Biol Chem. 2010 Feb 12;285(7):4951-63. doi: 10.1074/jbc.M109.087528. Epub 2009 Dec 9.
Intrinsically disordered proteins or protein regions play an important role in fundamental biological processes. During spliceosome activation, a large structural rearrangement occurs. The Prp19 complex and related factors are involved in the catalytic activation of the spliceosome. Recent mass spectrometric analyses have shown that Ski interaction protein (SKIP) and peptidylprolyl isomerase-like protein 1 (PPIL1) are Prp19-related factors that constitute the spliceosome B, B*, and C complexes. Here, we report that a highly flexible region of SKIP (SKIPN, residues 59-129) is intrinsically disordered. Upon binding to PPIL1, SKIPN undergoes a disorder-order transition. A highly conserved fragment of SKIP (residues 59-79) called the PPIL1-binding fragment (PBF) was sufficient to bind PPIL1. The structure of PBF.PPIL1 complex, solved by NMR, shows that PBF exhibits an ordered structure and interacts with PPIL1 through electrostatic and hydrophobic interactions. Three subfragments in the PBF (residues 59-67, 68-73, and 74-79) show hook-like backbone structure, and interactions between these subfragments are necessary for PBF.PPIL1 complex formation. PPIL1 is a cyclophilin family protein. It is recruited by SKIP into the spliceosome by a region other than the peptidylprolyl isomerase active site. This enables the active site of PPIL1 to remain open in the complex and still function as a peptidylprolyl cis/trans-isomerase or molecular chaperon to facilitate the folding of other proteins in the spliceosomes. The large disordered region in SKIP provides an interaction platform. Its disorder-order transition, induced by PPIL1 binding, may adapt the requirement for a large structural rearrangement occurred in the activation of spliceosome.
无规则蛋白或蛋白区域在基本的生物过程中发挥着重要作用。在剪接体激活过程中，会发生大规模的结构重排。Prp19 复合物和相关因子参与剪接体的催化激活。最近的质谱分析表明，Ski 相互作用蛋白（SKIP）和肽基脯氨酰顺反异构酶样蛋白 1（PPIL1）是与 Prp19 相关的因子，它们构成剪接体 B、B*和 C 复合物。在这里，我们报告说 SKIP 的一个高度灵活的区域（SKIPN，残基 59-129）是无规则的。与 PPIL1 结合后，SKIPN 经历了无序到有序的转变。SKIP 的一个高度保守片段（残基 59-79）称为 PPIL1 结合片段（PBF），足以与 PPIL1 结合。通过 NMR 解决的 PBF.PPIL1 复合物的结构表明，PBF 表现出有序的结构，并通过静电和疏水相互作用与 PPIL1 相互作用。PBF 中的三个亚片段（残基 59-67、68-73 和 74-79）显示出钩状的骨架结构，这些亚片段之间的相互作用对于 PBF.PPIL1 复合物的形成是必要的。PPIL1 是一种亲环素家族蛋白。它通过 SKIP 被招募到剪接体中，而不是通过肽基脯氨酰异构酶活性位点。这使得 PPIL1 的活性位点在复合物中保持开放，并仍然能够作为肽基脯氨酰顺/反异构酶或分子伴侣，促进剪接体中其他蛋白质的折叠。SKIP 中的大无序区域提供了一个相互作用平台。它与 PPIL1 结合诱导的无序到有序的转变，可能适应了剪接体激活过程中发生的大规模结构重排的要求。
