Sääf A, Andersson H, Gafvelin G, von Heijne G
Karolinska Institute Center for Structural Biochemistry, NOVUM, Huddinge, Sweden.
Mol Membr Biol. 1995 Apr-Jun;12(2):209-15. doi: 10.3109/09687689509027509.
We have analysed the translocation of a large periplasmic loop in the Escherichia coli MalF inner membrane protein when placed in different sequence contexts and under conditions when the function of the SecA protein is inhibited. The results show that the degree of SecA-dependence varies with sequence context: while translocation of the large loop in its normal context is only minimally affected by SecA inhibition, translocation is much more sensitive to SecA inhibition when the loop is placed in the context of other inner membrane proteins. Conversely, when the large MalF loop is replaced by segments from other proteins, translocation of those segments is again very sensitive to SecA inhibition. Thus, SecA-dependence is not an all-or-none phenomenon and is not only a simple function of, e.g. the length of a translocated segment or the hydrophobicity of the flanking transmembrane segments.
我们分析了大肠杆菌MalF内膜蛋白中一个大的周质环在置于不同序列环境时以及在SecA蛋白功能受到抑制的条件下的易位情况。结果表明，对SecA的依赖程度随序列环境而变化：在其正常环境中，大环的易位仅受到SecA抑制的轻微影响，而当该环置于其他内膜蛋白的环境中时，易位对SecA抑制更为敏感。相反，当大的MalF环被其他蛋白的片段取代时，这些片段的易位对SecA抑制同样非常敏感。因此，对SecA的依赖并非全有或全无的现象，也不仅仅是例如易位片段长度或侧翼跨膜片段疏水性的简单函数。
