Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
J Bacteriol. 2012 Aug;194(16):4415-25. doi: 10.1128/JB.00640-12. Epub 2012 Jun 15.
The bacterial dinucleotide second messenger c-di-GMP has emerged as a central molecule in regulating bacterial behavior, including motility and biofilm formation. Proteins for the synthesis and degradation of c-di-GMP and effectors for its signal transmission are widely used in the bacterial domain. Previous work established the GGDEF-EAL domain-containing receptor LapD as a central switch in Pseudomonas fluorescens cell adhesion. LapD senses c-di-GMP inside the cytosol and relays this signal to the outside by the differential recruitment of the periplasmic protease LapG. Here we identify the core components of an orthologous system in Legionella pneumophila. Despite only moderate sequence conservation at the protein level, key features concerning the regulation of LapG are retained. The output domain of the LapD-like receptor from L. pneumophila, CdgS9, binds the LapG ortholog involving a strictly conserved surface tryptophan residue. While the endogenous substrate for L. pneumophila LapG is unknown, the enzyme processed the corresponding P. fluorescens substrate, indicating a common catalytic mechanism and substrate recognition. Crystal structures of L. pneumophila LapG provide the first atomic models of bacterial proteases of the DUF920 family and reveal a conserved calcium-binding site important for LapG function.
细菌二核苷酸第二信使 c-di-GMP 已成为调节细菌行为（包括运动性和生物膜形成）的核心分子。用于 c-di-GMP 合成和降解的蛋白质以及其信号转导的效应物在细菌领域得到了广泛应用。先前的工作确定了含有 GGDEF-EAL 结构域的受体 LapD 是荧光假单胞菌细胞黏附的中央开关。LapD 在细胞质内感应 c-di-GMP，并通过周质蛋白酶 LapG 的差异募集将此信号传递到细胞外。在这里，我们鉴定了军团菌属中同源系统的核心成分。尽管在蛋白质水平上只有中等的序列保守性，但有关 LapG 调节的关键特征得以保留。来自嗜肺军团菌的 LapD 样受体的输出结构域 CdgS9 与涉及严格保守表面色氨酸残基的 LapG 同源物结合。虽然内源性军团菌 LapG 的底物未知，但该酶处理了相应的荧光假单胞菌底物，表明存在共同的催化机制和底物识别。军团菌属 LapG 的晶体结构提供了 DUF920 家族细菌蛋白酶的首个原子模型，并揭示了一个对 LapG 功能很重要的保守钙结合位点。
