Characterization of Periplastidal Compartment-Targeting Signals in Chlorarachniophytes
Characterization of Periplastidal Compartment-Targeting Signals in Chlorarachniophytes
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DOI：
10.1093/molbev/msq038
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发表时间：
2010-07-01
影响因子：
10.7
通讯作者：
Ishida, Ken-ichiro
中科院分区：
文献类型：
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作者：
Hirakawa, Yoshihisa;Gile, Gillian H.;Ishida, Ken-ichiro
次生质体是通过真核藻类的吞噬和保留而获得的，相对于陆地植物中更熟悉的初级质体，次生质体会产生额外的膜或对膜。在大多数情况下，内吞噬的藻类在整合过程中会失去真核基因组，但在两种藻类中，隐生藻类和绿蛛形藻类，次生质体在质周隔室（PPC）中保留了一个退化核，这是内膜和外膜对之间的真核细胞质残留。这些减少的基因组中缺少许多基本的管家基因，这表明它们现在在宿主细胞核中编码，它们的产物以PPC为目标。一种这样的核编码的ppc靶向蛋白，翻译延伸因子样（EFL）最近在chlorararachniophytes中被发现。它具有一个n端靶向序列，包括一个信号肽和一个类似于chlorarachninites的质体靶向蛋白的转运肽样序列（transit peptide like sequence， TPL），以及一个富含赖氨酸和天冬氨酸的亲水性c端延伸。在这里，我们描述了转化的氯蛛形纲植物细胞中ppc靶向EFL的N端和c端延伸的功能。使用绿色荧光蛋白作为报告分子，我们证明了TPL中几个带负电的氨基酸对于准确靶向PPC是必不可少的。我们的研究结果进一步揭示了c端延伸与n端质体靶向肽结合作为PPC保留信号，这表明质体和PPC蛋白可能在PPC中被分类。
Secondary plastids are acquired by the engulfment and retention of eukaryotic algae, which results in an additional surrounding membrane or pair of membranes relative to the more familiar primary plastids of land plants. In most cases, the endocytosed alga loses its eukaryotic genome as it becomes integrated, but in two algal groups, the cryptophytes and chlorarachniophytes, the secondary plastids retain a vestigial nucleus in the periplastidal compartment (PPC), the remnant eukaryotic cytoplasm between the inner and the outer membrane pairs. Many essential housekeeping genes are missing from these reduced genomes, suggesting that they are now encoded in the host nucleus and their products are targeted to the PPC. One such nucleus-encoded, PPC-targeted protein, the translation elongation factor like (EFL) was recently identified in chlorarachniophytes. It bears an N-terminal targeting sequence comprising a signal peptide and a transit peptide like sequence (TPL) similar to the plastid-targeted proteins of chlorarachniophytes as well as a hydrophilic C-terminal extension rich in lysine and aspartic acid. Here, we characterize the function of the N- and C-terminal extensions of PPC-targeted EFL in transformed chlorarachniophyte cells. Using green fluorescent protein as a reporter molecule, we demonstrate that several negatively charged amino acids within the TPL are essential for accurate targeting to the PPC. Our findings further reveal that the C-terminal extension functions as a PPC retention signal in combination with an N-terminal plastid-targeting peptide, which suggests that plastid and PPC proteins may be sorted in the PPC.