Heterogeneous surface expression of EspA translocon filaments by Escherichia coli O157:H7 is controlled at the posttranscriptional level
Heterogeneous surface expression of EspA translocon filaments by Escherichia coli O157:H7 is controlled at the posttranscriptional level
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DOI：
10.1128/iai.71.10.5900-5909.2003
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发表时间：
2003-10-01
影响因子：
3.1
通讯作者：
Gally, DL
中科院分区：
文献类型：
--
作者：
Roe, AJ;Yull, H;Gally, DL
肠道细菌的III型分泌系统能够将效应蛋白转位到宿主细胞中。产毒大肠埃希菌O157菌株的分泌蛋白包括易位装置的组件EspA、-B和-D，以及“效应”，如易位的内膜受体(TIR)和线粒体相关蛋白(MAP)。本研究研究了LEE4转位蛋白的调控，特别是EspA。在M9微量培养基中未检测到EspA细丝，而在改良了25 mM HEPES的最低基本培养基上仅有部分细菌有EspA细丝表达。EspA丝状菌的比例在指数期后期最高，之后菌丝迅速从细菌细胞表面消失。我们先前的研究表明，人和牛的O157：H7菌株在EspD分泌水平上显示出显著的差异。研究表明，表达EspA细丝的细菌种群比例与EspD分泌水平有关。通过使用β-半乳糖苷酶和绿色荧光蛋白(GFP)启动子的融合，证明了单个细菌表达EspA细丝的能力不能控制在LEE1-4操纵子转录水平。当使用LEEI-4翻译融合时，所有细菌，无论是否表达EspA细丝，都显示出同等水平的GFP表达。尽管如此，非分泌性细菌比例高的群体(低分泌者)的LEE4-espADB mRNA比分泌性细菌因此丝状菌的高比例群体(高分泌者)的群体更丰富。这项研究表明，虽然诱导LEEI-4表达需要特定的环境条件，但在细菌表面产生EspA细丝和分泌效应蛋白之前，存在进一步的检查点。在E.ColiO157：H7转位表达中，这个检查点是由作用于LEE4-espADB mRNA的转录后机制控制的。EspA细丝形成的异质性可能是由于控制这一转录后机制的调控因子的相位可变表达造成的。
Type III secretion systems of enteric bacteria enable translocation of effector proteins into host cells. Secreted proteins of verotoxigenic Escherichia coli O157 strains include components of a translocation apparatus, EspA, -B, and -D, as well as "effectors" such as the translocated intimin receptor (Tir) and the mitochondrion-associated protein (Map). This research has investigated the regulation of LEE4 translocon proteins, in particular EspA. EspA filaments could not be detected on the bacterial cell surface when E. coli O157:H7 was cultured in M9 minimal medium but were expressed from only a proportion of the bacterial population when cultured in minimal essential medium modified with 25 mM HEPES. The highest proportions of EspA-filamented bacteria were detected in late exponential phase, after which filaments were lost rapidly from the bacterial cell surface. Our previous research had shown that human and bovine E. coli O157:H7 strains exhibit marked differences in EspD secretion levels. Here it is demonstrated that the proportion of the bacterial population expressing EspA filaments was associated with the level of EspD secretion. The ability of individual bacteria to express EspA filaments was not controlled at the level of LEE1-4 operon transcription, as demonstrated by using both beta-galactosidase and green fluorescent protein (GFP) promoter fusions. All bacteria, whether expressing EspA filaments or not, showed equivalent levels of GFP expression when LEEI-4 translational fusions were used. Despite this, the LEE4-espADB mRNA was more abundant from populations with a high proportion of nonsecreting bacteria (low secretors) than from populations with a high proportion of secreting and therefore filamented bacteria (high secretors). This research demonstrates that while specific environmental conditions are required to induce LEEI-4 expression, a further checkpoint exists before EspA filaments are produced on the bacterial surface and secretion of effector proteins occurs. This checkpoint in E. coli O157:H7 translocon expression is controlled by a posttranscriptional mechanism acting on LEE4-espADB mRNA. The heterogeneity in EspA filamentation could arise from phase-variable expression of regulators that control this posttranscriptional mechanism.