Yuan Jianguo, Kight Alicia, Goforth Robyn L, Moore Misty, Peterson Eric C, Sakon Joshua, Henry Ralph
Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701, USA.
J Biol Chem. 2002 Aug 30;277(35):32400-4. doi: 10.1074/jbc.M206192200. Epub 2002 Jun 24.
The signal recognition particle (SRP) and its receptor (FtsY in prokaryotes) are essential for cotranslational protein targeting to the endoplasmic reticulum in eukaryotes and the cytoplasmic membrane in prokaryotes. An SRP/FtsY-like protein targeting/integration pathway in chloroplasts mediates the posttranslational integration of the light-harvesting chlorophyll a/b-binding protein (LHCP) into thylakoid membranes. GTP, chloroplast SRP (cpSRP), and chloroplast FtsY (cpFtsY) are required for LHCP integration into thylakoid membranes. Here, we report the reconstitution of the LHCP integration reaction with purified recombinant proteins and salt-washed thylakoids. Our data demonstrate that cpSRP and cpFtsY are the only soluble protein components required for LHCP integration. In addition, our studies reveal that ATP, though not absolutely required, remarkably stimulates LHCP integration into salt-washed thylakoids. ATP stimulates LHCP integration by a mechanism independent of the thylakoidal pH gradient (DeltapH) and exerts no detectable effect on the formation of the soluble LHCP-cpSRP-targeting complex. Taken together, our results indicate the participation of a thylakoid ATP-binding protein in LHCP integration.
信号识别颗粒（SRP）及其受体（原核生物中的FtsY）对于真核生物中蛋白质共翻译靶向内质网以及原核生物中蛋白质共翻译靶向细胞质膜至关重要。叶绿体中一种类似SRP/FtsY的蛋白质靶向/整合途径介导了捕光叶绿素a/b结合蛋白（LHCP）翻译后整合到类囊体膜中。LHCP整合到类囊体膜中需要GTP、叶绿体SRP（cpSRP）和叶绿体FtsY（cpFtsY）。在此，我们报道了利用纯化的重组蛋白和盐洗类囊体重构LHCP整合反应。我们的数据表明，cpSRP和cpFtsY是LHCP整合所需的仅有的可溶性蛋白质组分。此外，我们的研究表明，ATP虽不是绝对必需的，但能显著刺激LHCP整合到盐洗类囊体中。ATP通过一种独立于类囊体pH梯度（ΔpH）的机制刺激LHCP整合，并且对可溶性LHCP-cpSRP靶向复合物的形成没有可检测到的影响。综上所述，我们的结果表明一种类囊体ATP结合蛋白参与了LHCP整合。
