Korennykh Alexei V, Egea Pascal F, Korostelev Andrei A, Finer-Moore Janet, Zhang Chao, Shokat Kevan M, Stroud Robert M, Walter Peter
Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA.
Nature. 2009 Feb 5;457(7230):687-93. doi: 10.1038/nature07661. Epub 2008 Dec 14.
Aberrant folding of proteins in the endoplasmic reticulum activates the bifunctional transmembrane kinase/endoribonuclease Ire1. Ire1 excises an intron from HAC1 messenger RNA in yeasts and Xbp1 messenger RNA in metozoans encoding homologous transcription factors. This non-conventional mRNA splicing event initiates the unfolded protein response, a transcriptional program that relieves the endoplasmic reticulum stress. Here we show that oligomerization is central to Ire1 function and is an intrinsic attribute of its cytosolic domains. We obtained the 3.2-A crystal structure of the oligomer of the Ire1 cytosolic domains in complex with a kinase inhibitor that acts as a potent activator of the Ire1 RNase. The structure reveals a rod-shaped assembly that has no known precedence among kinases. This assembly positions the kinase domain for trans-autophosphorylation, orders the RNase domain, and creates an interaction surface for binding of the mRNA substrate. Activation of Ire1 through oligomerization expands the mechanistic repertoire of kinase-based signalling receptors.
内质网中蛋白质的异常折叠会激活双功能跨膜激酶/核糖核酸内切酶Ire1。Ire1会从酵母中的HAC1信使核糖核酸以及后生动物中的Xbp1信使核糖核酸中切除一个内含子，这些信使核糖核酸编码同源转录因子。这种非常规的信使核糖核酸剪接事件会启动未折叠蛋白反应，这是一种减轻内质网应激的转录程序。我们在此表明，寡聚化是Ire1功能的核心，并且是其胞质结构域的固有属性。我们获得了Ire1胞质结构域寡聚体与一种激酶抑制剂形成复合物的3.2埃晶体结构，该激酶抑制剂是Ire1核糖核酸酶的有效激活剂。该结构揭示了一种杆状聚集体，在激酶中尚无先例。这种聚集体将激酶结构域定位用于反式自磷酸化，排列核糖核酸酶结构域，并为信使核糖核酸底物的结合创造一个相互作用表面。通过寡聚化激活Ire1扩展了基于激酶的信号受体的作用机制。
