The Rickettsial Ankyrin Repeat Protein 2 Is a Type IV Secreted Effector That Associates with the Endoplasmic Reticulum
The Rickettsial Ankyrin Repeat Protein 2 Is a Type IV Secreted Effector That Associates with the Endoplasmic Reticulum
复制标题
DOI：
10.1128/mbio.00975-18
复制
发表时间：
2018-05-01
期刊：
影响因子：
6.4
通讯作者：
Hackstadt, Ted
中科院分区：
文献类型：
--
作者：
Lehman, Stephanie S.;Noriea, Nicholas F.;Hackstadt, Ted
立克次体（落基山斑疹热的蜱传病原体）菌株的毒力差异很大。立氏立克次体菌株的基因组比较已鉴定出无毒菌株中相对少量的差异基因。其中之一被注释为立克次氏体锚蛋白重复蛋白 2 (RARP-2)。 RARP-2 的同源物存在于所有立克次体菌株中，但无毒力菌株 Iowa 中的蛋白质相对于强毒力 Sheila Smith 菌株含有较大的内部缺失。 RARP-2 以 IV 型分泌系统依赖性方式分泌并暴露于宿主细胞胞浆。 Sheila Smith 的 RARP-2 与带有内质网 (ER) 标记的多层膜结构共定位，而爱荷华蛋白未显示与宿主细胞器的共定位，并且检测到蛋白水解降解的证据。 Sheila Smith RARP-2 在爱荷华立克次体中的过度表达将该无毒菌株的典型非裂解或不透明噬菌斑类型转化为与强毒 Sheila Smith 菌株相似的裂解噬菌斑表型。 Sheila Smith RARP-2 的预测蛋白水解活性位点的突变消除了裂解斑表型，但并未消除与宿主膜的关联。因此，RARP-2 是一种 IV 型分泌效应子，从立克次体释放到宿主细胞质中，以在感染过程中调节宿主过程。然而，Sheila Smith RARP-2 的过度表达并没有恢复爱荷华菌株在豚鼠模型中的毒力，这可能是由于立克次体的多因素性质！毒力.重要性 立克次体属成员是专性细胞内细菌，表现出一系列毒力，从无害的节肢动物内共生体到严重疾病的病原体。尽管可用基因组的数量不断增加，但关于立克次体的毒力决定因素却知之甚少。在这里，我们鉴定了一种含有锚蛋白重复序列的蛋白质 RARP-2，它在高毒力和无毒力的立克次体菌株（落基山斑疹热的病原体）之间存在差异。 RARP-2 由 IV 型分泌系统分泌到宿主细胞的细胞质中，与内质网相互作用并操纵内质网的结构。无毒株的 RARP-2 因 10 个锚蛋白重复单元中的 7 个丢失而被截短，但尽管被分泌，但无法改变 ER 结构。识别与毒力相关的立克次体因子将有助于了解疾病严重程度的区域和菌株特异性差异。
Strains of Rickettsia rickettsii, the tick-borne agent of Rocky Mountain spotted fever, vary considerably in virulence. Genomic comparisons of R. rickettsii strains have identified a relatively small number of genes divergent in an avirulent strain. Among these is one annotated as Rickettsia ankyrin repeat protein 2 (RARP-2). Homologs of RARP-2 are present in all strains of R. rickettsii, but the protein in the avirulent strain Iowa contains a large internal deletion relative to the virulent Sheila Smith strain. RARP-2 is secreted in a type IV secretion system-dependent manner and exposed to the host cell cytosol. RARP-2 of Sheila Smith colocalizes with multi-lamellar membranous structures bearing markers of the endoplasmic reticulum (ER), whereas the Iowa protein shows no colocalization with host cell organelles and evidence of proteolytic degradation is detected. Overexpression of Sheila Smith RARP-2 in R. rickettsii Iowa converts this avirulent strain's typically nonlytic or opaque plaque type to a lytic plaque phenotype similar to that of the virulent Sheila Smith strain. Mutation of a predicted proteolytic active site of Sheila Smith RARP-2 abolished the lytic plaque phenotype but did not eliminate association with host membrane. RARP-2 is thus a type IV secreted effector and released from the rickettsiae into the host cytosol to modulate host processes during infection. Overexpression of Sheila Smith RARP-2 did not, however, restore the virulence of the Iowa strain in a guinea pig model, likely due to the multifactorial nature of rickettsia! virulence.IMPORTANCE Members of the genus Rickettsia are obligate intracellular bacteria that exhibit a range of virulence from harmless endosymbionts of arthropods to the etiologic agents of severe disease. Despite the growing number of available genomes, little is known regarding virulence determinants of rickettsiae. Here, we have characterized an ankyrin repeat-containing protein, RARP-2, which differs between a highly virulent and an avirulent strain of R. rickettsii, the agent of Rocky Mountain spotted fever. RARP-2 is secreted by a type IV secretion system into the cytosol of the host cell, where it interacts with and manipulates the structure of the endoplasmic reticulum. RARP-2 from the avirulent strain is truncated by the loss of seven of 10 ankyrin repeat units but, although secreted, fails to alter ER structure. Recognition of those rickettsial factors associated with virulence will facilitate understanding of regional and strain-specific variation in severity of disease.