Mori H, Cline K
Horticultural Sciences Department and Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, Florida 32611-0690, USA.
J Biol Chem. 1998 May 8;273(19):11405-8. doi: 10.1074/jbc.273.19.11405.
Signal peptides that specifically direct precursor proteins to the thylakoid Delta pH pathway possess an N domain RR motif. Signal peptides that direct transport of bacterial proteins across a non-Sec export pathway possess an N domain RRXFLK consensus motif. Recent genetic studies suggest an evolutionary link between these two protein translocation pathways. To further explore this relationship, we examined the thylakoid targeting capability of the signal peptide for Escherichia coli hydrogenase 1 small subunit (HyaA) by linking it to plastocyanin and assaying the chimeric protein in an in vitro thylakoid transport assay. The chimeric precursor was transported across thylakoids with high efficiency. Transport was characteristic of the Delta pH but not the Sec pathway, i.e. it was eliminated by ionophores that dissipate the DeltapH but occurred in the absence of stromal extract or ATP. This result was confirmed by competition with chemical quantities of a Delta pH pathway precursor. This indicates that the HyaA signal peptide has the necessary elements for efficient and exclusive targeting to the Delta pH pathway and further supports the notion that the alternate targeting pathways in prokaryotes and plant thylakoids are analogous.
能将前体蛋白特异性导向类囊体ΔpH转运途径的信号肽具有一个N结构域RR基序。能将细菌蛋白跨非Sec输出途径转运的信号肽具有一个N结构域RRXFLK共有基序。最近的遗传学研究表明这两种蛋白质转运途径之间存在进化联系。为了进一步探究这种关系，我们通过将大肠杆菌氢化酶1小亚基（HyaA）的信号肽与质体蓝素连接，并在体外类囊体转运试验中检测嵌合蛋白，来研究其对类囊体的靶向能力。嵌合前体高效转运穿过类囊体。转运具有ΔpH途径而非Sec途径的特征，即它被能消除ΔpH的离子载体所阻断，但在没有基质提取物或ATP的情况下仍会发生。这一结果通过与化学计量的ΔpH途径前体竞争得到证实。这表明HyaA信号肽具有高效且特异性靶向ΔpH途径的必要元件，并进一步支持了原核生物和植物类囊体中交替靶向途径相似的观点。
