Wu Ye E, Hong Weizhe, Liu Chong, Zhang Lingqing, Chang Zengyi
National Laboratory of Protein Engineering and Plant Genetic Engineering, School of Life Sciences, Peking University, Beijing 100871, China.
Biochem J. 2008 Jun 1;412(2):389-97. doi: 10.1042/BJ20071682.
The extremely acidic environment of the mammalian stomach (pH 1-3) represents a stressful challenge for enteric pathogenic bacteria, including Escherichia coli, Shigella and Brucella. The hdeA (hns-dependent expression A) gene was found to be crucial for the survival of these enteric bacteria under extremely low pH conditions. We recently demonstrated that HdeA is able to exhibit chaperone-like activity exclusively within the stomach pH range by transforming from a well-folded conformation at higher pH values (above pH 3) into an unfolded conformation at extremely low pH values (below pH 3). This study was performed to characterize the action mechanisms and underlying specific structural features for HdeA to function in this unfolded conformation. In the present study, we demonstrate that the conserved 'amphiphilic' feature of HdeA, i.e. the exposure of the conserved hydrophobic region and highly charged terminal regions, is essential for exhibiting chaperone-like activity under extremely low pH conditions. Mutations that disrupt this amphiphilic feature markedly reduced the chaperone-like activity of HdeA. The results also strongly suggest that this acid-induced chaperone-like activity of HdeA is crucial for acid resistance of the enteric bacteria. Moreover, our new understanding of this amphiphilic structural feature of HdeA helps to better interpret how this unfolded (disordered) conformation could be functionally active.
哺乳动物胃内的极端酸性环境（pH值为1 - 3）对肠道病原菌来说是一个严峻的挑战，这些病原菌包括大肠杆菌、志贺氏菌和布鲁氏菌。hdeA（hns依赖表达A）基因被发现对于这些肠道细菌在极低pH条件下的存活至关重要。我们最近证明，HdeA能够通过在较高pH值（pH 3以上）时从折叠良好的构象转变为在极低pH值（pH 3以下）时的未折叠构象，仅在胃的pH范围内展现出类似伴侣蛋白的活性。本研究旨在表征HdeA在这种未折叠构象中发挥作用的作用机制及潜在的特定结构特征。在本研究中，我们证明了HdeA保守的“两亲性”特征，即保守疏水区域和高电荷末端区域的暴露，对于在极低pH条件下展现类似伴侣蛋白的活性至关重要。破坏这种两亲性特征的突变显著降低了HdeA的类似伴侣蛋白的活性。结果还强烈表明，HdeA这种酸诱导的类似伴侣蛋白的活性对于肠道细菌的耐酸性至关重要。此外，我们对HdeA这种两亲性结构特征的新认识有助于更好地解释这种未折叠（无序）构象如何能够具有功能活性。
