Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA 01003, USA.
Proc Natl Acad Sci U S A. 2013 Feb 19;110(8):3173-8. doi: 10.1073/pnas.1219229110. Epub 2013 Feb 4.
Chloroplast heat shock protein 90 (Hsp90C) represents a highly conserved subfamily of the Hsp90 family of molecular chaperones whose function has not been defined. We identified Hsp90C as a component that interacts with import intermediates of nuclear-encoded preproteins during posttranslational import into isolated chloroplasts. Hsp90C was specifically coprecipitated with a complex of protein import components, including Tic110, Tic40, Toc75, Tic22, and the stromal chaperones, Hsp93 and Hsp70. Radicicol, an inhibitor of Hsp90 ATPase activity, reversibly inhibited the import of a variety of preproteins during translocation across the inner envelope membrane, indicating that Hsp90C functions in membrane translocation into the organelle. Hsp90C is encoded by a single gene in Arabidopsis thaliana, and insertion mutations in the Hsp90C gene are embryo lethal, indicating an essential function for the chaperone in plant viability. On the basis of these results, we propose that Hsp90C functions within a chaperone complex in the chloroplast stroma to facilitate membrane translocation during protein import into the organelle.
叶绿体热休克蛋白 90（Hsp90C）是分子伴侣 HSP90 家族中高度保守的亚家族，其功能尚未确定。我们鉴定出 Hsp90C 是一种与核编码前体蛋白的翻译后导入到分离的叶绿体中时的进口中间体相互作用的成分。Hsp90C 与包括 Tic110、Tic40、Toc75、Tic22 和基质伴侣 Hsp93 和 Hsp70 在内的蛋白质导入组件复合物特异性共沉淀。Radicicol 是 HSP90 ATP 酶活性的抑制剂，可逆地抑制各种前体蛋白在穿过内膜转运时的导入，表明 Hsp90C 在线粒体膜转运中起作用。拟南芥中的 Hsp90C 由单个基因编码，并且 Hsp90C 基因的插入突变是胚胎致死的，表明该伴侣在植物活力中具有必需的功能。基于这些结果，我们提出 Hsp90C 在叶绿体基质中的伴侣复合物中发挥作用，以促进蛋白质导入细胞器时的膜转运。
