Zhang F, Yin Y, Arrowsmith C H, Ling V
Division of Molecular and Structural Biology, Ontario Cancer Institute, Canada.
Biochemistry. 1995 Apr 4;34(13):4193-201. doi: 10.1021/bi00013a007.
The secretion of the 107 kDa hemolysin A (HlyA) from Escherichia coli is mediated by membrane proteins hemolysin B (HlyB) and hemolysin D (HlyD). The signal for transport has been mapped to the C-terminal 60 amino acids of the HylA molecule. We have shown previously that the C-terminal 70 amino acids of leukotoxin (LktA) from Pasteurella hemolytica can substitute functionally for the HlyA signal sequence. This 70 amino acid peptide contains little primary sequence similarity to the HlyA signal sequence, and we have hypothesized that these signal sequences assume a similar higher-order structure which is recognized by the HlyB/D transporter. In the present study, we have expressed and purified small peptides containing the C-terminal 61 amino acids of HlyA and the C-terminal 70 amino acids of LktA. We show that these signal peptides are sufficient for secretion from E. coli in a HlyB/D dependent manner. Circular dichroism analyses show that both molecules exhibit common biophysical properties. In aqueous solution, they appear to be mainly unstructured, but in a membrane mimetic environment they assume a helical secondary structure. The conformational change observed for both peptides going from an aqueous to a membrane mimetic environment may be an important feature of these signal sequences necessary for their recognition and transport.
大肠杆菌分泌的107 kDa溶血素A（HlyA）是由膜蛋白溶血素B（HlyB）和溶血素D（HlyD）介导的。转运信号已定位到HylA分子的C末端60个氨基酸。我们之前已经表明，溶血巴斯德菌白细胞毒素（LktA）的C末端70个氨基酸在功能上可以替代HlyA信号序列。这个70个氨基酸的肽与HlyA信号序列几乎没有一级序列相似性，我们推测这些信号序列具有相似的高级结构，可被HlyB/D转运体识别。在本研究中，我们表达并纯化了含有HlyA C末端61个氨基酸和LktA C末端70个氨基酸的小肽。我们表明，这些信号肽足以以HlyB/D依赖的方式从大肠杆菌中分泌出来。圆二色性分析表明，这两种分子都表现出共同的生物物理特性。在水溶液中，它们似乎主要是无结构的，但在模拟膜的环境中，它们呈现出螺旋二级结构。从水溶液环境到模拟膜环境时，这两种肽观察到的构象变化可能是这些信号序列被识别和转运所必需的重要特征。
