Multiple conformational switches in a GTPase complex control co-translational protein targeting
Multiple conformational switches in a GTPase complex control co-translational protein targeting
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DOI：
10.1073/pnas.0808573106
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发表时间：
2009-02-10
影响因子：
11.1
通讯作者：
Shan, Shu-Ou
中科院分区：
文献类型：
--
作者：
Zhang, Xin;Schaffitzel, Christiane;Shan, Shu-Ou
“GTP酶开关”范式，其中GTP酶通过核苷酸交换因子（GEF）或GTP酶活化蛋白（GAP）的募集在活性的GTP结合状态和非活性的GDP结合状态之间切换，已被用于解释许多GTP酶的调节机制。该范例的一个值得注意的例外是由信号识别颗粒（SRP）和SRP受体（SR）中的两个GTP酶提供，其控制蛋白质向细胞膜的共翻译靶向。与经典的“GTdR开关”不同，SRP和SR在相互作用期间都经历了一系列离散的构象重排，最终导致其相互的GTdR激活。在这里，我们表明，在SRP-SR结合和激活过程中的这一系列重排提供了重要的控制点，以驱动和调节蛋白质靶向。使用实时荧光，我们表明，SRP核糖体的货物翻译新生多肽与信号序列加速SRP.SR复合物组装超过100倍，从而驱动货物的快速传递到膜。SRP. SRGTdR复合物中的一系列随后的重排提供了重要的驱动力，以在蛋白质靶向的后期阶段卸载货物。此外，该货物将SRP.SR复合物中的GTdR活化延迟8-12倍，产生了重要的时间窗口，其可以进一步提高蛋白质靶向的效率和保真度。因此，SRP和SR GTP酶在不招募外部调节因子的情况下构成了一个自给自足的系统，该系统提供了对复杂细胞过程的精确的空间和时间控制。
The "GTPase switch'' paradigm, in which a GTPase switches between an active, GTP-bound state and an inactive, GDP-bound state through the recruitment of nucleotide exchange factors (GEFs) or GTPase activating proteins (GAPs), has been used to interpret the regulatory mechanism of many GTPases. A notable exception to this paradigm is provided by two GTPases in the signal recognition particle (SRP) and the SRP receptor (SR) that control the co-translational targeting of proteins to cellular membranes. Instead of the classical "GTPase switch,'' both the SRP and SR undergo a series of discrete conformational rearrangements during their interaction with one another, culminating in their reciprocal GTPase activation. Here, we show that this series of rearrangements during SRP-SR binding and activation provide important control points to drive and regulate protein targeting. Using real-time fluorescence, we showed that the cargo for SRP ribosomes translating nascent polypeptides with signal sequences-accelerates SRP.SR complex assembly over 100-fold, thereby driving rapid delivery of cargo to the membrane. A series of subsequent rearrangements in the SRP.SR GTPase complex provide important driving forces to unload the cargo during late stages of protein targeting. Further, the cargo delays GTPase activation in the SRP.SR complex by 8-12 fold, creating an important time window that could further improve the efficiency and fidelity of protein targeting. Thus, the SRP and SR GTPases, without recruiting external regulatory factors, constitute a self-sufficient system that provides exquisite spatial and temporal control of a complex cellular process.