Patel Chetan N, Smith Virginia F, Randall Linda L
Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, USA.
Protein Sci. 2006 Jun;15(6):1379-86. doi: 10.1110/ps.062141006.
The general secretory, Sec, system translocates precursor polypeptides from the cytosol across the cytoplasmic membrane in Escherichia coli. SecB, a small cytosolic chaperone, captures the precursor polypeptides before they fold and delivers them to the membrane translocon through interactions with SecA. Both SecB and SecA display twofold symmetry and yet the complex between the two is stabilized by contacts that are distributed asymmetrically. Two distinct regions of interaction have been defined previously and here we identify a third. Calorimetric studies of complexes stabilized by different subsets of these interactions were carried out to determine the binding affinities and the thermodynamic parameters that underlie them. We show here that there is no change in affinity when either one of two contact areas out of the three is lacking. This fact and the asymmetry of the binding contacts may be important to the function of the complex in protein export.
在大肠杆菌中，一般分泌（Sec）系统将前体多肽从细胞质溶胶转运穿过细胞质膜。SecB是一种小的细胞质伴侣蛋白，它在这些前体多肽折叠之前捕获它们，并通过与SecA的相互作用将它们递送至膜转运体。SecB和SecA均呈现出双重对称性，但二者之间的复合物通过不对称分布的接触得以稳定。此前已经定义了两个不同的相互作用区域，在此我们鉴定出了第三个区域。我们对由这些相互作用的不同子集稳定的复合物进行了量热研究，以确定结合亲和力及其背后的热力学参数。我们在此表明，当三个接触区域中的两个区域中的任何一个缺失时，亲和力不会发生变化。这一事实以及结合接触的不对称性可能对该复合物在蛋白质输出中的功能很重要。
