2019年10月4日，加州大学伯克利分校的John Kuriyan和加拿大英属哥伦比亚大学的Sriram Subramaniam等研究人员合作在《科学》杂志发表论文，报道了二聚化B-Raf与14-3-3复合物的冷冻电镜结构。

研究人员利用冷冻电镜结构分析发现，磷酸化的B-Raf激酶结构域二聚体与14-3-3蛋白二聚体形成复合物，分辨率约为3.9埃，这显示出一种不对称排列，其中激酶处于经典的“活化”构象。该激酶C末端尾部的远侧区段以这种不对称排列与同源激酶的活性位点相互作用并阻断。C末端片段的删除降低了Raf活性。出乎意料的不对称四元结构说明了激酶抑制剂为何对Raf的反常激活，从而反映了一种先天的机制，即14-3-3促进了一个激酶的抑制，同时又保持了另一个激酶的活性。这些接触的构象调节可能为Raf抑制剂的开发提供新的机会。

据介绍，Raf激酶是重要的癌症药物靶标。矛盾的是，许多B-Raf抑制剂诱导Raf激酶的激活。

附：英文原文

Title: Cryo-EM structure of a dimeric B-Raf:14-3-3 complex reveals asymmetry in the active sites of B-Raf kinases

Author: Yasushi Kondo, Jana Ognjenovi, Saikat Banerjee, Deepti Karandur, Alan Merk, Kayla Kulhanek, Kathryn Wong, Jeroen P. Roose, Sriram Subramaniam, John Kuriyan

Issue&Volume: Volume 366 Issue 6461

Abstract: Raf kinases are important cancer drug targets. Paradoxically, many B-Raf inhibitors induce the activation of Raf kinases. Cryo–electron microscopy structural analysis of a phosphorylated B-Raf kinase domain dimer in complex with dimeric 14-3-3, at a resolution of ~3.9 angstroms, shows an asymmetric arrangement in which one kinase is in a canonical “active” conformation. The distal segment of the C-terminal tail of this kinase interacts with, and blocks, the active site of the cognate kinase in this asymmetric arrangement. Deletion of the C-terminal segment reduces Raf activity. The unexpected asymmetric quaternary architecture illustrates how the paradoxical activation of Raf by kinase inhibitors reflects an innate mechanism, with 14-3-3 facilitating inhibition of one kinase while maintaining activity of the other. Conformational modulation of these contacts may provide new opportunities for Raf inhibitor development.

DOI: 10.1126/science.aay0543

Source:https://science.sciencemag.org/content/366/6461/109