Mas Guillaume, Burmann Björn M, Sharpe Timothy, Claudi Beatrice, Bumann Dirk, Hiller Sebastian
Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland.
Sci Adv. 2020 Oct 21;6(43). doi: 10.1126/sciadv.abc5822. Print 2020 Oct.
The homotrimeric molecular chaperone Skp of Gram-negative bacteria facilitates the transport of outer membrane proteins across the periplasm. It has been unclear how its activity is modulated during its functional cycle. Here, we report an atomic-resolution characterization of the Skp monomer-trimer transition. We find that the monomeric state of Skp is intrinsically disordered and that formation of the oligomerization interface initiates folding of the α-helical coiled-coil arms via a unique "stapling" mechanism, resulting in the formation of active trimeric Skp. Native client proteins contact all three Skp subunits simultaneously, and accordingly, their binding shifts the Skp population toward the active trimer. This activation mechanism is shown to be essential for fitness in a mouse infection model. The coupled mechanism is a unique example of how an ATP-independent chaperone can modulate its activity as a function of the presence of client proteins.
革兰氏阴性菌的同三聚体分子伴侣Skp促进外膜蛋白穿过周质的转运。目前尚不清楚其活性在功能循环中是如何调节的。在此，我们报告了Skp单体-三聚体转变的原子分辨率特征。我们发现Skp的单体状态本质上是无序的，寡聚化界面的形成通过独特的“钉合”机制启动α-螺旋卷曲螺旋臂的折叠，从而形成活性三聚体Skp。天然的客户蛋白同时与Skp的所有三个亚基接触，因此，它们的结合使Skp群体向活性三聚体转变。这种激活机制在小鼠感染模型中被证明对适应性至关重要。这种偶联机制是一个独特的例子，说明了一种不依赖ATP的伴侣蛋白如何根据客户蛋白的存在来调节其活性。
