Processing the Polyprotein Precursor to Euglena LHCPII

细胞质合成的蛋白质转运到细胞器并插入细胞膜是生物学家面临的一个基本问题。通常，叶绿体蛋白是在游离核糖体上合成的，并在翻译后输入到叶绿体中；而内质网(ER)蛋白是在膜结合的核糖体上合成的，然后共翻译输入到内质网中。内质网和高尔基体发生蛋白水解性前体的成熟和分选，以运输到其最终的细胞内位置。免疫电子显微镜已将裸藻叶绿体蛋白LHCPII定位于高尔基体合成活跃的时期。Euglena pLHCPII是一种膜结合核糖体上合成的多聚蛋白。Euglena LHCPII的光诱导在伸长的起始或早期受翻译控制。综上所述，这些结果表明，Euglena LHCPII在输入叶绿体之前被共翻译运输到内质网和高尔基体中。这与高等植物和绿藻叶绿体直接翻译后吸收前体蛋白形成对比。本研究的目的是利用体内脉冲标记和细胞器分离以及体内对微粒体和叶绿体的转位研究(独立和顺序地)来描述Euglena将细胞质合成的蛋白质运输到叶绿体的新途径所需的步骤和涉及的胞内隔室。叶绿体膜的组装需要合成和运输来自不同细胞室的组成蛋白。这项研究将描绘光合酶复合体“捕光叶绿素蛋白II”合成的细胞位置，并阐明它被运输到发育中的叶绿体结构的机制。所获得的信息将增加我们对膜定位多酶复合体的生物合成和组装的理解。

The transport of cytoplasmically synthesized proteins to cellular organelles and insertion into membranes is a fundamental question confronting biologists. As a rule, chloroplast proteins are synthesized on free ribosomes and post-translationally imported into chloroplasts while Endoplasmic Reticulum (ER) proteins are synthesized on membrane bound ribosomes and co-translationally imported to the ER. Proteolytic precursor maturation and sorting for transport to their final intracellular site occurs in the ER and golgi. Immunoelectronmicroscopy has localized the Euglena chloroplast protein LHCPII to the golgi apparatus during times of active synthesis. Euglena pLHCPII is a polyprotein synthesized on membrane bound ribosomes. Photoinduction of Euglena LHCPII is translationally controlled at initiation or an early stage of elongation. Taken together, these results suggest that Euglena LHCPII is co-translationally transported into the ER and golgi apparatus prior to import into chloroplasts. This contrasts with the direct post-translational uptake of precursor proteins into higher plant and green algal chloroplasts. The purpose of this research is to use in vivo pulse labeling and organelle fractionation as well as in vivo translocation studies into microsmes and chloroplasts (independently and sequentially) to delineate the steps required and intracellular compartments involved in the novel pathway Euglena utilizes for the transport of cytoplasmically synthesized proteins to chloroplasts. %%% The assembly of chloroplast membranes requires the synthesis and transport of constituent proteins from various cellular compartments. This research will delineate the cellular site of synthesis of the photosynthetic enzyme complex "Light Harvesting Chlorophyll-Protein II" and elucidate the mechanism by which it is transported into the developing chloroplast structure. Information gained will increase our understanding of the biosynthesis and assembly of membrane-localized multienzyme complexes.