Mechanistic Differences between Two Conserved Classes of Small Heat Shock Proteins Found in the Plant Cytosol
Mechanistic Differences between Two Conserved Classes of Small Heat Shock Proteins Found in the Plant Cytosol
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DOI：
10.1074/jbc.m109.074088
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发表时间：
2010-04-09
影响因子：
4.8
通讯作者：
Vierling, Elizabeth
中科院分区：
文献类型：
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作者：
Basha, Eman;Jones, Christopher;Vierling, Elizabeth
小热休克蛋白（sHSP）和α-晶体蛋白是高度有效的，ATP-独立的伴侣，可以结合变性客户蛋白，以防止其不可逆的聚集。sHSP功能的一个模型表明，低聚sHSP通过在升高的温度下解离成二聚体或其他亚低聚物物质而被活化成客户结合形式。在这里，我们研究这个模型中的寡聚体结构和分子伴侣活性的两个保守类的细胞溶质的sHSPs在植物中，I类（CI）和II类（CII）蛋白质的比较。像CI sHSP一样，来自三种不同植物物种豌豆、小麦和拟南芥的重组CII sHSP是十二聚体，如通过纳米电喷雾质谱法所确定的。虽然在35至45 ° C下，所有三种Cl sHSP可逆地解离成二聚体，但CII sHSP在高温下保留寡聚体结构。然而，CII十二聚体是动态的并且快速交换亚基，但与Cl sHSP不同，交换单元看起来大于二聚体。十二聚体结构的差异还反映在CII蛋白不与CISHSP异源寡聚化的事实中。疏水探针bis-ANS的结合和有限的蛋白水解表明CII蛋白在高温下发生显著的可逆结构变化。所有三种重组CII蛋白比CI蛋白更有效地保护萤火虫荧光素酶在加热过程中不溶解。C1和CII蛋白在客户端保护中表现出严格的相加性。总之，结果表明，不同的sHSP可以通过不同的机制实现对客户蛋白的有效保护。
The small heat shock proteins (sHSPs) and alpha-crystallins are highly effective, ATP-independent chaperones that can bind denaturing client proteins to prevent their irreversible aggregation. One model of sHSP function suggests that the oligomeric sHSPs are activated to the client-binding form by dissociation at elevated temperatures to dimers or other sub-oligomeric species. Here we examine this model in a comparison of the oligomeric structure and chaperone activity of two conserved classes of cytosolic sHSPs in plants, the class I (CI) and class II (CII) proteins. Like the CI sHSPs, recombinant CII sHSPs from three divergent plant species, pea, wheat, and Arabidopsis, are dodecamers as determined by nano-electrospray mass spectrometry. While at 35 to 45 degrees C, all three CI sHSPs reversibly dissociate to dimers, the CII sHSPs retain oligomeric structure at high temperature. The CII dodecamers are, however, dynamic and rapidly exchange subunits, but unlike CI sHSPs, the exchange unit appears larger than a dimer. Differences in dodecameric structure are also reflected in the fact that the CII proteins do not hetero-oligomerize with CI sHSPs. Binding of the hydrophobic probe bis-ANS and limited proteolysis demonstrate CII proteins undergo significant, reversible structural changes at high temperature. All three recombinant CII proteins more efficiently protect firefly luciferase from insolubilization during heating than do the CI proteins. The CI and CII proteins behave strictly additively in client protection. In total, the results demonstrate that different sHSPs can achieve effective protection of client proteins by varied mechanisms.