Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.
PLoS One. 2013 Jul 23;8(7):e70384. doi: 10.1371/journal.pone.0070384. Print 2013.
Hsp70 chaperones are involved in multiple biological processes and are recruited to specific processes by designated J domain-containing cochaperones, or J proteins. To understand the evolution and functions of chloroplast Hsp70s and J proteins, we identified the Arabidopsis chloroplast J protein constituency using a combination of genomic and proteomic database searches and individual protein import assays. We show that Arabidopsis chloroplasts have at least 19 J proteins, the highest number of confirmed J proteins for any organelle. These 19 J proteins are classified into 11 clades, for which cyanobacteria and glaucophytes only have homologs for one clade, green algae have an additional three clades, and all the other 7 clades are specific to land plants. Each clade also possesses a clade-specific novel motif that is likely used to interact with different client proteins. Gene expression analyses indicate that most land plant-specific J proteins show highly variable expression in different tissues and are down regulated by low temperatures. These results show that duplication of chloroplast Hsp70 in land plants is accompanied by more than doubling of the number of its J protein cochaperones through adding new J proteins with novel motifs, not through duplications within existing families. These new J proteins likely recruit chloroplast Hsp70 to perform tissue specific functions related to biosynthesis rather than to stress resistance.
热休克蛋白 70 伴侣参与多种生物过程，并通过指定的含有 J 结构域的共伴侣蛋白或 J 蛋白被招募到特定的过程中。为了了解叶绿体 Hsp70 和 J 蛋白的进化和功能，我们使用基因组和蛋白质组数据库搜索以及单个蛋白质导入测定的组合，鉴定了拟南芥叶绿体 J 蛋白组成。我们表明，拟南芥叶绿体至少有 19 种 J 蛋白，这是任何细胞器中确认的 J 蛋白数量最多的。这 19 种 J 蛋白被分为 11 个分支，其中蓝细菌和绿藻只有一个分支的同源物，绿藻有另外三个分支，而其他 7 个分支都是陆地植物所特有的。每个分支还具有一个分支特异性的新基序，可能用于与不同的客户蛋白相互作用。基因表达分析表明，大多数陆地植物特异性 J 蛋白在不同组织中的表达具有高度可变性，并受到低温的下调。这些结果表明，陆地植物叶绿体 Hsp70 的复制伴随着其 J 蛋白共伴侣数量的增加，超过了两倍，这是通过添加具有新基序的新 J 蛋白来实现的，而不是通过现有家族内的重复来实现的。这些新的 J 蛋白可能会招募叶绿体 Hsp70 来执行与生物合成相关的组织特异性功能，而不是应激抗性。
