Calorimetric analyses of the interaction between SecB and its ligands
Calorimetric analyses of the interaction between SecB and its ligands
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DOI：
10.1002/pro.5560070514
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发表时间：
1998-05-01
期刊：
影响因子：
8
通讯作者：
Hardy, SJS
中科院分区：
文献类型：
--
作者：
Randall, LL;Topping, TB;Hardy, SJS
SecB是大肠杆菌中的分子伴侣，致力于将蛋白质从细胞质输出到周质和外膜。它的功能是在输出蛋白质折叠成其天然结构之前将其前体结合并递送到易位装置，从而使其保持在跨膜易位的胜任状态。SecB的天然配体是含有前导序列的前体蛋白。文献中有许多报道表明SecB不特异性识别前导肽。然而，两个公开的研究已经得出结论，前导肽是识别元件（Watanabe M，Blobel G. 1989. Cell 58：685-705; Watanabe M，Blobel G. 1995. Proc Natl Acad Sci USA 92：10133-10136）。在这项工作中，我们使用滴定量热法表明，SecB结合两个生理配体，其中包含前导序列，没有更高的亲和力比相同的分子缺乏其前导序列。事实上，对于一个配体，前导序列的存在降低了亲和力。因此，可以得出结论，前导序列对结合能没有正贡献。
SecB is a chaperone in Escherichia coli dedicated to export of proteins from the cytoplasm to the periplasm and outer membrane. It functions to bind and deliver precursors of exported proteins to the translocation apparatus before they fold into their native structures, thus maintaining them in a competent state for translocation across the membrane. The natural ligands of SecB are precursor proteins containing leader sequences. There are numerous reports in the literature indicating that SecB does not specifically recognize the leader peptides. However, two published investigations have concluded that the leader peptide is the recognition element (Watanabe M, Blobel G. 1989. Cell 58:685-705; Watanabe M, Blobel G. 1995. Proc Natl Acad Sci USA 92:10133-10136). In this work we use titration calorimetry to show that SecB binds two physiological ligands, which contain leader sequences, with no higher affinity than the same molecules lacking their leader sequences. Indeed, for one ligand the presence of the leader sequence reduces the affinity. Therefore, it can be concluded that the leader sequence provides no positive contribution to the binding energy.