PelN Is a New Pectate Lyase of Dickeya dadantii with Unusual Characteristics
PelN Is a New Pectate Lyase of Dickeya dadantii with Unusual Characteristics
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DOI：
10.1128/jb.02118-12
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发表时间：
2013-05-01
影响因子：
3.2
通讯作者：
Hugouvieux-Cotte-Pattat, Nicole
中科院分区：
文献类型：
--
作者：
Hassan, Susan;Shevchik, Vladimir E.;Hugouvieux-Cotte-Pattat, Nicole
植物病原细菌Dickeya dadantii 产生多种果胶分解酶，这些酶在软腐病中起主要作用。八种特征化的内果胶裂解酶由 II 型分泌系统 Out 分泌到细胞外培养基中。它们裂解果胶的内部糖苷键，导致植物组织浸渍。 D. dadantii 果胶酸裂合酶属于不同的家族，即 PL1、PL2、PL3 和 PL9。对 D. dadantii 3937 基因组的分析揭示了编码 PL9 家族新蛋白的基因，该家族已经包括分泌性内切胶裂解酶 PelL 和周质外切胶裂解酶 PelX。我们证明 PelN 是 Out 系统分泌的一种额外的细胞外蛋白。然而，PelN 有一些不寻常的特征。尽管大多数果胶酸裂合酶需要非常碱性的 pH 值和 Ca2+ 才能发挥其活性，但 PelN 活性在 pH 7.4 和存在 Fe2+ 作为辅助因子的情况下达到最佳。 PelN 仅受果胶甲酯化程度的微弱影响。在PelL结构的基础上构建的PelN结构模型表明，PelL全局拓扑及其催化氨基酸在PelN中是保守的。显着的差异涉及 PelN 表面额外环的存在，以及 PelN 中芳香族残基取代参与底物结合的 PelL 带电残基。 pelN 表达受不同环境条件的影响，例如 pH、渗透压和温度。它由抑制子 KdgR 和 PecS 以及激活子 GacA（D. dadanii 果胶酶基因的三个调节子）控制。由于 pelN 突变体对菊苣叶的毒力降低，因此 PelN 酶在植物感染中发挥作用，尽管其比活性较低且需要不寻常的辅因子。
The plant-pathogenic bacterium Dickeya dadantii produces several pectinolytic enzymes that play a major role in the soft-rot disease. Eight characterized endopectate lyases are secreted in the extracellular medium by the type II secretion system, Out. They cleave internal glycosidic bonds of pectin, leading to plant tissue maceration. The D. dadantii pectate lyases belong to different families, namely, PL1, PL2, PL3, and PL9. Analysis of the D. dadantii 3937 genome revealed a gene encoding a new protein of the PL9 family, which already includes the secreted endopectate lyase PelL and the periplasmic exopectate lyase PelX. We demonstrated that PelN is an additional extracellular protein secreted by the Out system. However, PelN has some unusual characteristics. Although most pectate lyases require a very alkaline pH and Ca2+ for their activity, the PelN activity is optimal at pH 7.4 and in the presence of Fe2+ as a cofactor. PelN is only weakly affected by the degree of pectin methyl esterification. The PelN structural model, constructed on the basis of the PelL structure, suggests that the PelL global topology and its catalytic amino acids are conserved in PelN. Notable differences concern the presence of additional loops at the PelN surface, and the replacement of PelL charged residues, involved in substrate binding, by aromatic residues in PelN. The pelN expression is affected by different environmental conditions, such as pH, osmolarity, and temperature. It is controlled by the repressors KdgR and PecS and by the activator GacA, three regulators of D. dadantii pectinase genes. Since a pelN mutant had reduced virulence on chicory leaves, the PelN enzyme plays a role in plant infection, despite its low specific activity and its unusual cofactor requirement.