植酸InsP6激活YopJ家族效应蛋白的分子机制研究

YopJ家族效应蛋白是一类由III型分泌系统（T3SS）转运的致病性蛋白，广泛存在于动物致病菌和植物致病菌中。作为一类非经典的乙酰转移酶，YopJ家族效应蛋白的独特之处在于它们需要与宿主细胞中的植酸（InsP6）结合才能被激活，这在其他类型的乙酰转移酶中是没有发现过的，但具体的机制还有待深入研究。我们前期的实验解析了apo状态下YopJ家族成员PopP2的晶体结构，通过跟我们以往发表的激活状态的PopP2结构对比发现两者之间的构象差异超乎想象。结合初步的生化实验和计算机模拟，我们推测InsP6可以诱导位于催化核心域C-端的fold-switching结构域发生一个由α-螺旋向β-折叠的转变，进而稳定底物结合口袋。接下来我们希望通过NMR和更多的生化实验来验证这一结论。我们的工作将不仅仅揭示YopJ家族蛋白的活化机制，还将为深入研究fold-switching蛋白提供新的模型。

The Yersinia outer protein J (YopJ) family effectors are widely employed in the type III secretion system by both plant and animal pathogens. As non-canonical acetyltransferases, the enzymatic activities of YopJ family effectors are allosterically activated by the eukaryote-specific ligand inositol hexaphosphate (InsP6). However, the molecular mechanism underpinning remains undefined. Here we present the crystal structure of PopP2, a YopJ family member secreted by the plant pathogen Ralstonia solanacearum, in apo state. Structural comparison of apo-PopP2 with our previously reported InsP6-bound PopP2 complexes reveals a substantial conformational readjustment centered the substrate-binding site. Combined biochemical and computational analyses further identify a mechanism in which the association of InsP6 with PopP2 induces an α-helix-to-β-strand transition in the catalytic core, thus stabilizing the substrate recognition helix to form the target protein binding pocket. We will carry out NMR study and more biochemical anylysis to confirm our discovery. Together, our study will uncover the molecular basis governing InsP6-mediated allosteric regulation of YopJ family acetyltransferases and further expands the paradigm of fold-switching proteins.