Around 100 proteins are produced inside the chloroplast but the vast majority must be imported. These proteins are synthesized in the cytosol as preproteins with cleavable targeting sequences. Several plastid types ot...Around 100 proteins are produced inside the chloroplast but the vast majority must be imported. These proteins are synthesized in the cytosol as preproteins with cleavable targeting sequences. Several plastid types other than chloroplasts exist. During plant development, one plastid type may be converted to another, a process referred to as plastid transition (Jarvis and Lopez-Juez, 2013). During plastid transitions, proteome remodeling occurs, and one set of imported proteins is replaced by another that is functionally adapted (Kleffmann et al., 2007). Moreover, plastid proteomes are known to be regulated in an environmentdependent fashion, and chloroplasts may respond to changing light conditions by regulating the composition and abundance of photosynthetic complexes.展开更多
Subcellular organelles in eukaryotes are surrounded by lipid membranes.In an endomembrane system,vesicle trafficking is the primary mechanism for the delivery of organellar proteins to specific organelles.However,orga...Subcellular organelles in eukaryotes are surrounded by lipid membranes.In an endomembrane system,vesicle trafficking is the primary mechanism for the delivery of organellar proteins to specific organelles.However,organellar proteins for chloroplasts,mitochondria,the nucleus,and peroxisomes that are translated in the cytosol are directly imported into their target organelles.Chloroplasts are a plant-specific organelle with outer and inner envelope membranes,a dual-membrane structure that is similar to mitochondria.Interior chloroplast proteins translated by cytosolic ribosomes are thus translocated through TOC and TIC complexes(translocons in the outer and inner envelope of chloroplasts,respectively),with stromal ATPase motor proteins playing a critical role in pulling pre-proteins through these import channels.Over the last three decades,the identity and function of TOC/TIC components and stromal motor proteins have been actively investigated,which has shed light on the action mechanisms at a molecular level.However,there remains some disagreement over the exact composition of TIC complexes and genuine stromal motor proteins.In this review,we discuss recent findings on the mechanisms by which proteins are translocated through TOC/TIC complexes and discuss future prospects for this field of research.展开更多
叶绿体作为植物及藻类细胞中含有内外双层被膜的细胞器,能够通过光合作用过程将光能转化为化学能。大部分的叶绿体蛋白由细胞核基因编码,其前体蛋白是在细胞质中的80S核糖体上合成的。前体蛋白在转运肽的引导下,通过跨越叶绿体外被膜和...叶绿体作为植物及藻类细胞中含有内外双层被膜的细胞器,能够通过光合作用过程将光能转化为化学能。大部分的叶绿体蛋白由细胞核基因编码,其前体蛋白是在细胞质中的80S核糖体上合成的。前体蛋白在转运肽的引导下,通过跨越叶绿体外被膜和内被膜的路径被传送进入叶绿体内部,进而到达发挥其生物学功能的目的微区。目前已知的前体蛋白转运的一个主要途径是通过叶绿体外被膜转运子(translocon in the outer envelope membrane of chloroplast, TOC)和内被膜转运子(translocon in the inner envelope membrane of chloroplast, TIC),在二者的协同作用下前体蛋白得以跨越双层被膜进入叶绿体。文章回顾了TOC-TIC超复合物的结构生物学研究进展,并深入探讨了各组件的功能特性以及前体蛋白易位至叶绿体内部的潜在途径和调控机制。展开更多
叶绿体外膜转运蛋白(translocon of the outer membrane of chloroplasts,TOC)介导了数千种位于细胞质中由细胞核编码的前体蛋白的识别与初始转运,对叶绿体生物合成及正常行使生物学功能具有重要作用。为明确番茄TOC复合体组分及其表达...叶绿体外膜转运蛋白(translocon of the outer membrane of chloroplasts,TOC)介导了数千种位于细胞质中由细胞核编码的前体蛋白的识别与初始转运,对叶绿体生物合成及正常行使生物学功能具有重要作用。为明确番茄TOC复合体组分及其表达特性,本研究基于番茄(Solanum lycopersicum)全基因组数据对番茄TOC复合体进行组分鉴定,并对其染色体定位、基因结构、保守基序、系统进化及弱光胁迫下表达模式等进行了分析。结果表明,番茄基因组中鉴定到10个TOC组分,分布于8条染色体上,分为4个基因家族,同一家族中的成员具有相似的基因结构和基序。e Plant提供的组织表达数据显示,TOC复合体不同组分在番茄中的表达具有组织特异性。qRT-PCR分析发现,番茄果实成熟过程中TOC复合体组分基因表达水平高于叶片组织,在这一过程中SlToc34-1、SlToc159-1和SlToc75表达上调,SlToc34-2、SlToc159-2和SlToc120表达下调;弱光胁迫处理下SlToc159-2、SlToc34-1和SlToc120表达水平均受到抑制,SlToc159-1和SlToc34-2没有明显的变化。研究成功克隆了SlToc159-2、SlToc34-1和SlToc34-2基因的cDNA序列,它们的氨基酸推导序列与拟南芥TOC组分蛋白具有很高的同源性,表明番茄是一种新的研究TOC复合体的有效模式植物。本研究为进一步探究番茄TOC复合体组分的功能提供参考。展开更多
Sec61β, a subunit of the Sec61 translocon complex, is not essential in yeast and commonly used as a marker of endoplasmic reticulum （ER）. In higher eukaryotes, such as Drosophila, deletion of Sec61β causes lethali...Sec61β, a subunit of the Sec61 translocon complex, is not essential in yeast and commonly used as a marker of endoplasmic reticulum （ER）. In higher eukaryotes, such as Drosophila, deletion of Sec61β causes lethality, but its physiological role is unclear. Here, we show that Sec61β interacts directly with microtubules. Overex- pression of Sec61β containing small epitope tags, but not a RFP tag, induces dramatic bundling of the ER and microtubule. A basic region in the cytosolic domain of Sec61β is critical for microtubule association. Depletion of Sec61β induces ER stress in both mammalian cells and Caenorhabditis elegans, and subsequent restoration of ER homeostasis correlates with the microtubule binding ability of Sec61β. Loss of Sec61β causes increased mobility of translocon complexes and reduced level of membrane-bound ribosomes. These results suggest that Sec61β may stabilize protein translocation by linking translocon complex to micro- tubule and provide insight into the physiological function of ER-microtubule interaction.展开更多
Preprotein import into chloroplasts depends on macromolecular machineries in the outer and inner chloroplast envelope membrane （TOC and TIC）. It was suggested that both machineries are interconnected by components o...Preprotein import into chloroplasts depends on macromolecular machineries in the outer and inner chloroplast envelope membrane （TOC and TIC）. It was suggested that both machineries are interconnected by components of the intermembrane space （IMS）. That is, amongst others, Tic22, of which two closely related isoforms exist in Arabidopsis thaliana, namely atTic22-III and atTic22-IV. We investigated the function of Tic22 in vivo by analyzing T-DNA insertion lines of the corresponding genes. While the T-DNA insertion in the individual genes caused only slight defects, a double mutant of both isoforms showed retarded growth, a pale phenotype under high-light conditions, a reduced import rate, and a reduction in the photosynthetic performance of the plants. The latter is supported by changes in the metabolite content of mutant plants when compared to wild-type. Thus, our results support the notion that Tic22 is directly involved in chloroplast preprotein import and might point to a particular importance of Tic22 in chloroplast biogenesis at times of high import rates.展开更多
基金the Swiss National Science Foundation (31003A_156998 and 31003A_176191).
文摘Around 100 proteins are produced inside the chloroplast but the vast majority must be imported. These proteins are synthesized in the cytosol as preproteins with cleavable targeting sequences. Several plastid types other than chloroplasts exist. During plant development, one plastid type may be converted to another, a process referred to as plastid transition (Jarvis and Lopez-Juez, 2013). During plastid transitions, proteome remodeling occurs, and one set of imported proteins is replaced by another that is functionally adapted (Kleffmann et al., 2007). Moreover, plastid proteomes are known to be regulated in an environmentdependent fashion, and chloroplasts may respond to changing light conditions by regulating the composition and abundance of photosynthetic complexes.
基金supported by an NRF grant funded by the MSIT(grant NRF-2020R1A2C4002294)supported by a National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(No.2019R1A2B5B03099982)。
文摘Subcellular organelles in eukaryotes are surrounded by lipid membranes.In an endomembrane system,vesicle trafficking is the primary mechanism for the delivery of organellar proteins to specific organelles.However,organellar proteins for chloroplasts,mitochondria,the nucleus,and peroxisomes that are translated in the cytosol are directly imported into their target organelles.Chloroplasts are a plant-specific organelle with outer and inner envelope membranes,a dual-membrane structure that is similar to mitochondria.Interior chloroplast proteins translated by cytosolic ribosomes are thus translocated through TOC and TIC complexes(translocons in the outer and inner envelope of chloroplasts,respectively),with stromal ATPase motor proteins playing a critical role in pulling pre-proteins through these import channels.Over the last three decades,the identity and function of TOC/TIC components and stromal motor proteins have been actively investigated,which has shed light on the action mechanisms at a molecular level.However,there remains some disagreement over the exact composition of TIC complexes and genuine stromal motor proteins.In this review,we discuss recent findings on the mechanisms by which proteins are translocated through TOC/TIC complexes and discuss future prospects for this field of research.
文摘叶绿体作为植物及藻类细胞中含有内外双层被膜的细胞器,能够通过光合作用过程将光能转化为化学能。大部分的叶绿体蛋白由细胞核基因编码,其前体蛋白是在细胞质中的80S核糖体上合成的。前体蛋白在转运肽的引导下,通过跨越叶绿体外被膜和内被膜的路径被传送进入叶绿体内部,进而到达发挥其生物学功能的目的微区。目前已知的前体蛋白转运的一个主要途径是通过叶绿体外被膜转运子(translocon in the outer envelope membrane of chloroplast, TOC)和内被膜转运子(translocon in the inner envelope membrane of chloroplast, TIC),在二者的协同作用下前体蛋白得以跨越双层被膜进入叶绿体。文章回顾了TOC-TIC超复合物的结构生物学研究进展,并深入探讨了各组件的功能特性以及前体蛋白易位至叶绿体内部的潜在途径和调控机制。
文摘叶绿体外膜转运蛋白(translocon of the outer membrane of chloroplasts,TOC)介导了数千种位于细胞质中由细胞核编码的前体蛋白的识别与初始转运,对叶绿体生物合成及正常行使生物学功能具有重要作用。为明确番茄TOC复合体组分及其表达特性,本研究基于番茄(Solanum lycopersicum)全基因组数据对番茄TOC复合体进行组分鉴定,并对其染色体定位、基因结构、保守基序、系统进化及弱光胁迫下表达模式等进行了分析。结果表明,番茄基因组中鉴定到10个TOC组分,分布于8条染色体上,分为4个基因家族,同一家族中的成员具有相似的基因结构和基序。e Plant提供的组织表达数据显示,TOC复合体不同组分在番茄中的表达具有组织特异性。qRT-PCR分析发现,番茄果实成熟过程中TOC复合体组分基因表达水平高于叶片组织,在这一过程中SlToc34-1、SlToc159-1和SlToc75表达上调,SlToc34-2、SlToc159-2和SlToc120表达下调;弱光胁迫处理下SlToc159-2、SlToc34-1和SlToc120表达水平均受到抑制,SlToc159-1和SlToc34-2没有明显的变化。研究成功克隆了SlToc159-2、SlToc34-1和SlToc34-2基因的cDNA序列,它们的氨基酸推导序列与拟南芥TOC组分蛋白具有很高的同源性,表明番茄是一种新的研究TOC复合体的有效模式植物。本研究为进一步探究番茄TOC复合体组分的功能提供参考。
文摘Sec61β, a subunit of the Sec61 translocon complex, is not essential in yeast and commonly used as a marker of endoplasmic reticulum （ER）. In higher eukaryotes, such as Drosophila, deletion of Sec61β causes lethality, but its physiological role is unclear. Here, we show that Sec61β interacts directly with microtubules. Overex- pression of Sec61β containing small epitope tags, but not a RFP tag, induces dramatic bundling of the ER and microtubule. A basic region in the cytosolic domain of Sec61β is critical for microtubule association. Depletion of Sec61β induces ER stress in both mammalian cells and Caenorhabditis elegans, and subsequent restoration of ER homeostasis correlates with the microtubule binding ability of Sec61β. Loss of Sec61β causes increased mobility of translocon complexes and reduced level of membrane-bound ribosomes. These results suggest that Sec61β may stabilize protein translocation by linking translocon complex to micro- tubule and provide insight into the physiological function of ER-microtubule interaction.
文摘Preprotein import into chloroplasts depends on macromolecular machineries in the outer and inner chloroplast envelope membrane （TOC and TIC）. It was suggested that both machineries are interconnected by components of the intermembrane space （IMS）. That is, amongst others, Tic22, of which two closely related isoforms exist in Arabidopsis thaliana, namely atTic22-III and atTic22-IV. We investigated the function of Tic22 in vivo by analyzing T-DNA insertion lines of the corresponding genes. While the T-DNA insertion in the individual genes caused only slight defects, a double mutant of both isoforms showed retarded growth, a pale phenotype under high-light conditions, a reduced import rate, and a reduction in the photosynthetic performance of the plants. The latter is supported by changes in the metabolite content of mutant plants when compared to wild-type. Thus, our results support the notion that Tic22 is directly involved in chloroplast preprotein import and might point to a particular importance of Tic22 in chloroplast biogenesis at times of high import rates.
