Yamanaka H, Nomura T, Fujii Y, Okamoto K
Department of Biochemistry, Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Tokushima, Yamashiro, Tokushima, 770-8514, Japan.
Microb Pathog. 1998 Sep;25(3):111-20. doi: 10.1006/mpat.1998.0211.
Escherichia coli heat-stable enterotoxin Ip (STIp) is a typical extracellular toxin consisting of 18 amino acid residues synthesized as a precursor of pre (amino acid residues 1 to 19), pro (amino acid residues 20 to 54), and mature (amino acid residues 55 to 72) regions. STIp synthesized in the cytoplasm must cross the inner and outer membranes to migrate into the extracellular environment. Previous studies showed that the precursor translocates across the inner membrane utilizing the general export pathway consisting of Sec proteins. However, it remains unclear how it crosses the outer membrane. In this study, we examined the effects of mutation of the tolC gene which encodes an E. coli outer membrane protein, TolC, on the release of STIp into the extracellular environment. The mutation reduced the amount of STIp released into culture supernatant and increased the amount of STIp accumulated in the periplasm. This indicates that TolC mediates the translocation of STIp across the outer membrane. The inability to transfer STIp in the periplasm into the culture supernatant was restored by introduction of the tolC gene into the mutant cells. In the mouse intestinal loop assay, living cells of the mutants did not show a positive response, but wild-type cells did. These results showed that TolC is involved in the translocation of STIp across the outer membrane.
大肠杆菌热稳定肠毒素Ip（STIp）是一种典型的细胞外毒素，由18个氨基酸残基组成，以pre（氨基酸残基1至19）、pro（氨基酸残基20至54）和成熟（氨基酸残基55至72）区域的前体形式合成。在细胞质中合成的STIp必须穿过内膜和外膜才能迁移到细胞外环境中。先前的研究表明，前体利用由Sec蛋白组成的一般输出途径穿过内膜。然而，它如何穿过外膜仍不清楚。在本研究中，我们研究了编码大肠杆菌外膜蛋白TolC的tolC基因突变对STIp释放到细胞外环境中的影响。该突变减少了释放到培养上清液中的STIp量，并增加了周质中积累的STIp量。这表明TolC介导了STIp穿过外膜的转运。通过将tolC基因导入突变细胞，恢复了周质中STIp不能转移到培养上清液中的情况。在小鼠肠袢试验中，突变体的活细胞没有显示出阳性反应，但野生型细胞有。这些结果表明TolC参与了STIp穿过外膜的转运。
