Mating Pair Formation Homologue TraG Is a Variable Membrane Protein Essential for Contact-Independent Type IV Secretion of Chromosomal DNA by Neisseria gonorrhoeae
Mating Pair Formation Homologue TraG Is a Variable Membrane Protein Essential for Contact-Independent Type IV Secretion of Chromosomal DNA by Neisseria gonorrhoeae
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DOI：
10.1128/jb.02098-12
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发表时间：
2013-04-01
影响因子：
3.2
通讯作者：
Dillard, Joseph P.
中科院分区：
文献类型：
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作者：
Kohler, Petra L.;Chan, Yolande A.;Dillard, Joseph P.
淋病奈瑟菌使用 IV 型分泌系统 (T4SS) 将染色体 DNA 分泌到周围环境中。 DNA可有效转化群体中的淋球菌，这种DNA捐赠机制可能有助于该物种的高度遗传多样性。与其他 F 样 T4SS 类似，淋球菌 T4SS 需要一种假定的膜蛋白 TraG 来进行 DNA 转移。在 F 质粒和相关系统中，同源蛋白在菌毛产生、交配对稳定和进入排除中发挥作用。我们表征了淋病奈瑟菌中 TraG 的定位、膜拓扑和变异。 TraG被发现是一种内膜蛋白，具有一个大的周质区域和一个大的细胞质区域。每个淋球菌菌株都携带 traG 的三个不同等位基因之一。发现携带 traG 最小等位基因的菌株缺乏肽聚糖酶基因 atlA，但携带肽聚糖内肽酶基因代替 atlA。纯化的内肽酶在体外降解淋球菌肽聚糖，切断肽交联。尽管其他两个 traG 等位基因在菌株 MS11 中具有 DNA 分泌功能，但最小的 traG 不支持 DNA 分泌。尽管需要交配对稳定同源物，静态共培养转化实验表明DNA转移对核酸酶敏感并且需要受体主动摄取，从而证明转移是通过转化而不是接合发生的。总之，这些结果表明 TraG 在 DNA 输出过程中起作用，而不是特定于结合，并且不同形式的 TraG 会影响可以运输的底物。
Neisseria gonorrhoeae uses a type IV secretion system (T4SS) to secrete chromosomal DNA into the surrounding milieu. The DNA is effective in transforming gonococci in the population, and this mechanism of DNA donation may contribute to the high degree of genetic diversity in this species. Similar to other F-like T4SSs, the gonococcal T4SS requires a putative membrane protein, TraG, for DNA transfer. In F-plasmid and related systems, the homologous protein acts in pilus production, mating pair stabilization, and entry exclusion. We characterized the localization, membrane topology, and variation of TraG in N. gonorrhoeae. TraG was found to be an inner-membrane protein with one large periplasmic region and one large cytoplasmic region. Each gonococcal strain carried one of three different alleles of traG. Strains that carried the smallest allele of traG were found to lack the peptidoglycanase gene atlA but carried a peptidoglycan endopeptidase gene in place of atlA. The purified endopeptidase degraded gonococcal peptidoglycan in vitro, cutting the peptide cross-links. Although the other two traG alleles functioned for DNA secretion in strain MS11, the smallest traG did not support DNA secretion. Despite the requirement for a mating pair stabilization homologue, static coculture transformation experiments demonstrated that DNA transfer was nuclease sensitive and required active uptake by the recipient, thus demonstrating that transfer occurred by transformation and not conjugation. Together, these results demonstrate the TraG acts in a process of DNA export not specific to conjugation and that different forms of TraG affect what substrates can be transported.