Department of Biology, Wilfrid Laurier University, Waterloo, ON N2L 3C5, Canada.
Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada.
Int J Mol Sci. 2022 Jan 29;23(3):1571. doi: 10.3390/ijms23031571.
Plastids are a dynamic class of organelle in plant cells that arose from an ancient cyanobacterial endosymbiont. Over the course of evolution, most genes encoding plastid proteins were transferred to the nuclear genome. In parallel, eukaryotic cells evolved a series of targeting pathways and complex proteinaceous machinery at the plastid surface to direct these proteins back to their target organelle. Chloroplasts are the most well-characterized plastids, responsible for photosynthesis and other important metabolic functions. The biogenesis and function of chloroplasts rely heavily on the fidelity of intracellular protein trafficking pathways. Therefore, understanding these pathways and their regulation is essential. Furthermore, the chloroplast outer membrane proteome remains relatively uncharted territory in our understanding of protein targeting. Many key players in the cytosol, receptors at the organelle surface, and insertases that facilitate insertion into the chloroplast outer membrane remain elusive for this group of proteins. In this review, we summarize recent advances in the understanding of well-characterized chloroplast outer membrane protein targeting pathways as well as provide new insights into novel targeting signals and pathways more recently identified using a bioinformatic approach. As a result of our analyses, we expand the known number of chloroplast outer membrane proteins from 117 to 138.
质体是植物细胞中一类具有动态特征的细胞器，起源于古老的蓝细菌内共生体。在进化过程中，大多数编码质体蛋白的基因转移到核基因组中。与此同时，真核细胞在质体表面进化出一系列靶向途径和复杂的蛋白质机器，以将这些蛋白质引导回其靶细胞器。叶绿体是研究最深入的质体，负责光合作用和其他重要的代谢功能。叶绿体的生物发生和功能严重依赖于细胞内蛋白质运输途径的保真度。因此，了解这些途径及其调控机制至关重要。此外，叶绿体外膜蛋白组在我们对蛋白质靶向的理解中仍然是一个相对未知的领域。对于这组蛋白质，质体细胞质中的许多关键因子、细胞器表面的受体以及促进插入叶绿体外膜的插入酶仍然难以捉摸。在这篇综述中，我们总结了近年来对已充分研究的叶绿体外膜蛋白靶向途径的理解的最新进展，并通过生物信息学方法提供了对最近发现的新型靶向信号和途径的新见解。通过我们的分析，我们将已知的叶绿体外膜蛋白数量从 117 个扩展到 138 个。
