Sites of interaction between SecA and the chaperone SecB, two proteins involved in export
Sites of interaction between SecA and the chaperone SecB, two proteins involved in export
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DOI：
10.1110/ps.03410104
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发表时间：
2004-04-01
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;Crane, JM;Hardy, SJS
SecB是大肠杆菌中的一种小的四聚体细胞质伴侣，通过保持前体多肽的规范构象并将其传递给SecA来促进前体多肽的输出，SecA是膜结合易位装置的外围成员。几个实验室已经提出，当SecA沿着输出途径与各种成分相互作用时，它会经历构象变化，这对其功能至关重要。在这里，我们报告了SecA和SecB分子之间相互作用的细节，它们可能作为构象开关。相互作用的一个位点涉及SecA的最后c端21个氨基酸，这些氨基酸带正电并含有锌。SecA二聚体的每个亚基的C端与SecB四聚体的每个二聚体形成的平面p片接触。在这里，我们证明了SecB的极端C端α -螺旋和SecA上的一个位点之间存在第二次相互作用，虽然尚未定义，但与SecA的C端不同。我们用滴定量热法研究了相互作用的能量学，并用沉降速度离心法表征了由两种相互作用或单独相互作用稳定的配合物的水动力学性质。
SecB, a small tetrameric cytosolic chaperone in Escherichia coli, facilitates the export of precursor polypeptides by maintaining them in a normative conformation and passing them to SecA, which is a peripheral member of the membrane-bound translocation apparatus. It has been proposed by several laboratories that as SecA interacts with various components along the export pathway, it undergoes conformational changes that are crucial to its function. Here we report details of molecular interactions between SecA and SecB, which may serve as conformational switches. One site of interaction involves the final C-terminal 21 amino acids of SecA, which are positively charged and contain zinc. The C terminus of each subunit of the SecA dimer makes contact with the flat P-sheet that is formed by each dimer of the SecB tetramer. Here we demonstrate that a second interaction exists between the extreme C-terminal alpha-helix of SecB and a site on SecA, as yet undefined but different from the C terminus of SecA. We investigated the energetics of the interactions by titration calorimetry and characterized the hydrodynamic properties of complexes stabilized by both interactions or each interaction singly using sedimentation velocity centrifugation.