Division of Applied Life Science (BK21 and WCU Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju 660-701, Republic of Korea.
Plant Physiol Biochem. 2013 Sep;70:368-73. doi: 10.1016/j.plaphy.2013.05.039. Epub 2013 Jun 5.
The seven members of the 90-kDa heat shock protein (Hsp90) family encode highly conserved molecular chaperones essential for cell survival in Arabidopsis thaliana. Hsp90 are abundant proteins, localized in different compartments with AtHsp90.1-4 in the cytosol and AtHsp90.5-7 in different organelles. Among the AtHsp90, AtHsp90.1, is stress-inducible and shares comparatively low sequence identity with the constitutively expressed AtHsp90.2-4. Even though abundant information is available on mammalian cytosolic Hsp90 proteins, it is unknown whether cytosolic Hsp90 proteins display different structural and functional properties. We have now analyzed two A. thalianas cytosolic Hsp90s, AtHsp90.1 and AtHsp90.3, for functional divergence. AtHsp90.3 showed higher holdase chaperone activity than AtHsp90.1, although both AtHsp90s exhibited effective chaperone activity. Size-exclusion chromatography revealed different oligomeric states distinguishing the two Hsp90 proteins. While AtHsp90.1 exists in several oligomeric states, including monomers, dimers and higher oligomers, AtHsp90.3 exists predominantly in a high oligomeric state. High oligomeric state of AtHsp90.1 showed higher holdase chaperone activity than the respective monomer or dimer states. When high oligomeric forms of AtHsp90.1 and AtHsp90.3 are reduced by DTT, activity was reduced compared to that found in the native high oligomeric state. In addition, ATP-dependent foldase chaperone activity of AtHsp90.3 was higher with strong intrinsic ATPase activity than that of AtHsp90.1. As a conclusion, the two A. thaliana cytosolic Hsp90 proteins display different functional activities depending on structural differences, implying functional divergence although the proteins are localized to the same sub-cellular organelle.
七名 90kDa 热休克蛋白 (Hsp90) 家族成员编码高度保守的分子伴侣，对拟南芥细胞存活至关重要。Hsp90 是丰富的蛋白质，定位于不同的隔室中，AtHsp90.1-4 存在于细胞质中，AtHsp90.5-7 存在于不同的细胞器中。在 AtHsp90 中，AtHsp90.1 是应激诱导的，与组成型表达的 AtHsp90.2-4 相比，具有相对较低的序列同一性。尽管关于哺乳动物细胞质 Hsp90 蛋白有大量信息，但尚不清楚细胞质 Hsp90 蛋白是否表现出不同的结构和功能特性。我们现在分析了两种拟南芥细胞质 Hsp90，AtHsp90.1 和 AtHsp90.3，以研究其功能分化。AtHsp90.3 表现出比 AtHsp90.1 更高的持家伴侣活性，尽管两种 AtHsp90 都表现出有效的伴侣活性。排阻色谱显示两种 Hsp90 蛋白的不同寡聚状态。虽然 AtHsp90.1 存在于几种寡聚状态中，包括单体、二聚体和更高的寡聚体，但 AtHsp90.3 主要存在于高寡聚状态。AtHsp90.1 的高寡聚状态显示出比相应的单体或二聚体状态更高的持家伴侣活性。当用 DTT 还原 AtHsp90.1 和 AtHsp90.3 的高寡聚形式时，与在天然高寡聚状态下发现的活性相比，活性降低。此外，AtHsp90.3 的 ATP 依赖性折叠酶伴侣活性具有比 AtHsp90.1 更高的内在 ATPase 活性。总之，两种拟南芥细胞质 Hsp90 蛋白显示出不同的功能活性，这取决于结构差异，尽管这些蛋白质定位于相同的亚细胞细胞器。
