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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Disulfide oxidoreductase activity of Shigella flexneri is required for release of Ipa proteins and invasion of epithelial cells.
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Disulfide oxidoreductase activity of Shigella flexneri is required for release of Ipa proteins and invasion of epithelial cells.

机译：弗氏志贺氏菌的二硫键氧化还原酶活性是释放Ipa蛋白和侵袭上皮细胞所必需的。

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摘要

Secretion of IpaB, IpaC, and IpaD proteins of Shigella flexneri, essential for the invasion of epithelial cells, requires a number of proteins encoded by the spa and mxi loci on the large plasmid. Introduction of dsbA::Tn5 into S.flexneri from Escherichia coli K-12 reduced invasiveness, which resulted from a decrease in the capacity to release IpaB, IpaC, and IpaD proteins into the external medium. Examination of the surface-presented Ipa proteins of the dsbA mutant, however, revealed Ipa proteins at levels similar to those on wild-type cells. Since the defective phenotype was similar to that of the spa32 mutant of S. flexneri and the Spa32 sequence possessed two Cys residues, the effect of dsbA mutation of the folding structure of Spa32 under reducing conditions and on the surface expression of Spa32 was investigated. The results indicated that Spa32 was a disulfide-containing protein whose correctly folded structure was required for its presentation on the outer membrane. Indeed, replacing either oneof the two Cys residues in Spa32 with Ser by site-directed mutagenesis reduced its capacity to release Ipa proteins into the external medium and led to the accumulation of Spa32 protein in the periplasm. These results indicated that the DsbA protein performs an essential function during the invasion of mammalian cells, by facilitating transport of the Spa32 protein across the outer membrane.
机译：弗氏志贺氏菌的IpaB，IpaC和IpaD蛋白质的分泌对于上皮细胞的侵袭至关重要，它需要由大质粒上的spa和mxi位点编码的许多蛋白质。将dsbA :: Tn5从大肠杆菌K-12引入弗氏链球菌减少了侵袭性，这是由于释放IpaB，IpaC和IpaD蛋白到外部培养基中的能力降低所致。然而，对dsbA突变体表面呈现的Ipa蛋白的检测显示，Ipa蛋白的水平与野生型细胞上的相似。由于缺陷表型类似于弗氏链球菌的spa32突变体，并且Spa32序列具有两个Cys残基，因此研究了在还原条件下Spa32的折叠结构的dsbA突变对Spa32的表面表达的影响。结果表明，Spa32是一种含二硫键的蛋白质，其正确折叠的结构对于其在外膜上的呈递是必需的。实际上，通过定点诱变用Ser替换Spa32中两个Cys残基之一会降低其将Ipa蛋白释放到外部介质中的能力，并导致Spa32蛋白在周质中积累。这些结果表明，DsbA蛋白通过促进Spa32蛋白跨外膜的转运，在哺乳动物细胞侵袭过程中起着至关重要的作用。

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