MacAB Is Involved in the Secretion of Escherichia coli Heat-Stable Enterotoxin II
MacAB Is Involved in the Secretion of Escherichia coli Heat-Stable Enterotoxin II
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DOI：
10.1128/jb.00853-08
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发表时间：
2008-12-01
影响因子：
3.2
通讯作者：
Okamoto, Keinosuke
中科院分区：
文献类型：
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作者：
Yamanaka, Hiroyasu;Kobayashi, Hidetomo;Okamoto, Keinosuke
产肠毒素大肠杆菌产生的耐热肠毒素(ST)是一种引起宿主水样腹泻的胞外肽毒素。已经发现了两种类型的STS，STI和STII。这两种STS都是以前体蛋白的形式合成的，然后在释放到周质中后转化为具有分子内二硫键的活性形式。活性的STS最终通过TolC制造的隧道穿过外膜转移。然而，目前尚不清楚在周质中形成的活性STS是如何被引导到TolC通道的。已知内膜及其周质附属蛋白中的几个转运蛋白与TolC结合，形成一个三部分转运系统。因此，我们希望这些转运体也能作为TolC的合作伙伴，将STS从周质输出到外部。在本研究中，我们利用不同转运蛋白基因(acrAB、acrEF、emrAB、emrKY、mdtEF、macAB和Yojhi)被敲除的大肠杆菌BL21(DE3)突变体进行了脉冲追逐实验，并分析了这些菌株中STS的分泌。结果表明，在macAB突变体中，STII的胞外分泌显著减少，毒素分子聚集在周质中，而本研究使用的任何突变体对STI的分泌都没有影响。通过将含有macAB基因的pACYC184导入细胞，恢复了macAB突变体中STII的周质停滞。这些结果表明，MacB及其附属蛋白MacA的三磷酸腺苷结合盒转运体MacAB参与了STII从周质到外部的转运。由于已有报道MacAB与TolC合作，我们认为MacAB-TolC系统捕获周质STII分子并将毒素分子输出到外部。
The heat-stable enterotoxin ( ST) produced by enterotoxigenic Escherichia coli is an extracellular peptide toxin that evokes watery diarrhea in the host. Two types of STs, STI and STII, have been found. Both STs are synthesized as precursor proteins and are then converted to the active forms with intramolecular disulfide bonds after being released into the periplasm. The active STs are finally translocated across the outer membrane through a tunnel made by TolC. However, it is unclear how the active STs formed in the periplasm are led to the TolC channel. Several transporters in the inner membrane and their periplasmic accessory proteins are known to combine with TolC and form a tripartite transport system. We therefore expect such transporters to also act as a partner with TolC to export STs from the periplasm to the exterior. In this study, we carried out pulse-chase experiments using E. coli BL21(DE3) mutants in which various transporter genes (acrAB, acrEF, emrAB, emrKY, mdtEF, macAB, and yojHI) had been knocked out and analyzed the secretion of STs in those strains. The results revealed that the extracellular secretion of STII was largely decreased in the macAB mutant and the toxin molecules were accumulated in the periplasm, although the secretion of STI was not affected in any mutant used in this study. The periplasmic stagnation of STII in the macAB mutant was restored by the introduction of pACYC184, containing the macAB gene, into the cell. These results indicate that MacAB, an ATP-binding cassette transporter of MacB and its accessory protein, MacA, participates in the translocation of STII from the periplasm to the exterior. Since it has been reported that MacAB cooperates with TolC, we propose that the MacAB-TolC system captures the periplasmic STII molecules and exports the toxin molecules to the exterior.