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首页> 外文期刊>Journal of Molecular Biology >Type II protein secretion in gram-negative pathogenic bacteria: The studyof the structure/secretion relationships of the cellulase CeI5 (formerlyEGZ) from Erwinia chrysanthemi
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Type II protein secretion in gram-negative pathogenic bacteria: The studyof the structure/secretion relationships of the cellulase CeI5 (formerlyEGZ) from Erwinia chrysanthemi

机译：革兰氏阴性致病菌中II型蛋白的分泌：欧文氏杆菌纤维素酶CeI5（以前为EGZ）的结构/分泌关系的研究

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Erwinia chrysanthemi, a Gram-negative plant pathogen, secretes the cellulase Cel5 (formerly EGZ) via the type II secretion pathway (referred to as Out). Cel5 is composed of two domains, a large N-terminal catalytic domain (390 amino acid residues) and a small C-terminal cellulose-binding domain (62 amino acid residues) separated by a linker region. A combination of mutagenesis and structural analysis permitted us to investigate the structure/secretion relationships with respect to the catalytic domain of Cel5. The 3D structure of the catalytic domain was solved by molecular replacement at 2.3 Angstrom resolution. Cel5 exhibits the (beta/alpha)(8) structural fold and two extra-barrel features. Our previous genetic study based upon tRNA-mediated suppression allowed us to predict positions of importance in the molecule in relation to structure and catalysis. Remarkably, all of the predictions proved to be correct when compared with the present structural information. Mutations of Arg57, which is located at the heart of the catalytic domain, allowed us to test the consequences of structural modifications on the secretion efficiency. The results revealed that secretability imposes remarkably strong constraints upon folding. In particular, an Arg-to-His mutation yielded a species that folded to a stable conformation close to, but distinct from the wild-type, which however was not secretable. We discuss the relationships between folding of a protein in the periplasm, en route to the cell exterior, and presentation of secretion information. We propose that different solutions have been selected for type II secreted exoproteins in order to meet the constraints imposed by their interaction with their respective secretion machineries. We propose that evolutionary pressure has led to the adaptation of different secretion motifs for different type II exoproteins.
机译：革兰氏阴性植物病原体欧文氏菌（Erwinia chrysanthemi）通过II型分泌途径（称为Out）分泌纤维素酶Cel5（以前为EGZ）。 Cel5由两个结构域组成，一个大的N末端催化结构域（390个氨基酸残基）和一个小的C末端纤维素结合结构域（62个氨基酸残基），被一个接头区域隔开。诱变和结构分析相结合，使我们能够研究与Cel5催化结构域有关的结构/分泌关系。催化域的3D结构通过2.3埃分辨率的分子置换解决。 Cel5具有（beta / alpha）（8）的结构折叠和两个桶外特征。我们之前基于tRNA介导的抑制作用的遗传研究使我们能够预测分子中与结构和催化有关的重要位置。值得注意的是，与当前的结构信息相比，所有的预测都被证明是正确的。位于催化域核心的Arg57突变使我们能够测试结构修饰对分泌效率的影响。结果表明，秘密性对折叠施加了明显的约束。特别是，从Arg到His的突变产生了一个折叠成稳定构象的物种，该构型接近但不同于野生型，但后者是不可分泌的。我们讨论了周质中蛋白质折叠，进入细胞外部以及分泌信息的表达之间的关系。我们建议为II型分泌的外泌蛋白选择不同的解决方案，以满足它们与其各自分泌机制相互作用所施加的限制。我们提出进化压力已经导致针对不同的II型外蛋白的不同分泌基序的适应。

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