Hou Jennifer Y, Sauer Robert T, Baker Tania A
Department of Biology, 68-523, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
Nat Struct Mol Biol. 2008 Mar;15(3):288-94. doi: 10.1038/nsmb.1392. Epub 2008 Feb 24.
Adaptor proteins modify substrate recognition by AAA+ ATPases. We examined how the adaptor ClpS regulates substrate choice by the Escherichia coli protease ClpAP. Binding of six ClpS molecules to a ClpA hexamer enhanced N-end-rule substrate degradation and inhibited ssrA-tagged protein proteolysis. Substoichiometric ClpS binding allowed intermediate degradation of both substrate types, revealing that adaptor stoichiometry influences substrate choice. ClpS controls substrate selection using distinct mechanisms. The N-terminal segment is essential for delivering N-end-rule substrates but dispensable for ssrA-protein inhibition. We tested existing models for ClpS action and found that ClpS does not block recognition of ssrA-tagged substrates by steric occlusion and that adaptor-mediated tethering of N-end-rule substrates to ClpAP was insufficient to explain facilitated delivery. We propose that ClpS functions, at least in part, as an allosteric effector of ClpAP, broadening our understanding of how AAA+ adaptors control substrate selection.
衔接蛋白可改变AAA+ ATP酶对底物的识别。我们研究了衔接蛋白ClpS如何调节大肠杆菌蛋白酶ClpAP对底物的选择。六个ClpS分子与一个ClpA六聚体的结合增强了N端规则底物的降解，并抑制了带有ssrA标签的蛋白质的蛋白水解。亚化学计量的ClpS结合允许两种底物类型的中间降解，这表明衔接蛋白的化学计量会影响底物选择。ClpS使用不同的机制控制底物选择。N端片段对于递送N端规则底物至关重要，但对于抑制ssrA蛋白则是可有可无的。我们测试了现有的ClpS作用模型，发现ClpS不会通过空间位阻来阻止对带有ssrA标签的底物的识别，并且衔接蛋白介导的将N端规则底物拴系到ClpAP上不足以解释其促进递送的作用。我们提出，ClpS至少部分地作为ClpAP的变构效应器发挥作用，这拓宽了我们对AAA+衔接蛋白如何控制底物选择的理解。
