Hwang Fu Yu-Hsien, Huang William Y C, Shen Kuang, Groves Jay T, Miller Thomas, Shan Shu-Ou
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, United States.
Department of Chemistry, University of California at Berkeley, Berkeley, United States.
Elife. 2017 Jul 28;6:e25885. doi: 10.7554/eLife.25885.
The signal recognition particle (SRP) delivers ~30% of the proteome to the eukaryotic endoplasmic reticulum, or the bacterial plasma membrane. The precise mechanism by which the bacterial SRP receptor, FtsY, interacts with and is regulated at the target membrane remain unclear. Here, quantitative analysis of FtsY-lipid interactions at single-molecule resolution revealed a two-step mechanism in which FtsY initially contacts membrane via a Dynamic mode, followed by an SRP-induced conformational transition to a Stable mode that activates FtsY for downstream steps. Importantly, mutational analyses revealed extensive auto-inhibitory mechanisms that prevent free FtsY from engaging membrane in the Stable mode; an engineered FtsY pre-organized into the Stable mode led to indiscriminate targeting in vitro and disrupted FtsY function in vivo. Our results show that the two-step lipid-binding mechanism uncouples the membrane association of FtsY from its conformational activation, thus optimizing the balance between the efficiency and fidelity of co-translational protein targeting.
信号识别颗粒（SRP）将约30%的蛋白质组输送到真核生物的内质网或细菌的质膜。细菌SRP受体FtsY在靶膜上相互作用并受到调控的确切机制仍不清楚。在这里，单分子分辨率下对FtsY与脂质相互作用的定量分析揭示了一种两步机制，其中FtsY最初通过动态模式接触膜，随后由SRP诱导构象转变为稳定模式，从而激活FtsY进行下游步骤。重要的是，突变分析揭示了广泛的自抑制机制，这些机制可防止游离的FtsY以稳定模式与膜结合；预先组织成稳定模式的工程化FtsY导致体外靶向无差别，并破坏体内FtsY功能。我们的结果表明，两步脂质结合机制将FtsY的膜结合与其构象激活解偶联，从而优化了共翻译蛋白质靶向的效率和保真度之间的平衡。
