Jiao, W., Hong, W., Li, P., Sun. S., Ma., J., Qian, M., Hu, M., and Chang, Z. (2008) “The dramatically increased chaperone activity of small heat-shock protein IbpB is retained for an extended period of time after the stress condition is removed”, Biochem. J., 410:63-70.

sHSP (small heat-shock protein) IbpB (inclusion-body-binding protein B) from Escherichia coli is known as an ATP-independent holding chaperone which prevents the insolubilization of aggregation-prone proteins by forming stable complexes with them. It was found that the chaperone function of IbpB is greatly modulated by the ambient temperature, i.e. when the temperature increases from normal to heat-shock, the chaperone activity of IbpB is dramatically elevated to a level that allows it to effectively bind the aggregation-prone client proteins. Although it is generally believed that the release and refolding of the client protein from the sHSPs depends on the aid of the ATP-dependent chaperones such as Hsp (heat-shock protein) 70 and Hsp100 when the ambient temperature recovers from heat-shock to normal, the behaviour of the sHSPs during this recovery stage has not yet been investigated. In the present study, we examined the behaviour and properties of IbpB upon temperature decrease from heat-shock to normal. We found that IbpB, which becomes functional only under heat-shock conditions, retains the chaperone activity for an extended period of time after the heat-shock stress condition is removed. A detail comparison demonstrates that such preconditioned IbpB is distinguished from the non-preconditioned IbpB by a remarkable conformational transformation, including a significant increase in the flexibility of the N- and C-terminal regions, as well as enhanced dynamic subunit dissociation/reassociation. Intriguingly, the preconditioned IbpB displayed a dramatic decrease in its surface hydrophobicity, suggesting that the exposure of hydrophobic sites might not be the sole determinant for IbpB to exhibit chaperone activity. We propose that the maintenance of the chaperone activity for such ‘holdases’ as sHSPs would be important for cells to recover from heat-shock stress.

中文翻译

      题目：小分子热休克蛋白IbpB之被极大增强的分子伴侣活性在胁迫条件被去除后仍旧能够长时间保持

      摘要：大肠杆菌的小分子热休克蛋白IbpB（最初被命名为包涵体结合蛋白）被发现为一种不依赖ATP的“持有性”分子伴侣蛋白，它通过与具有聚集倾向的“客户”蛋白形成稳定的复合物而阻止其形成不可溶性聚集体。我们以前的研究发现，IbpB蛋白的分子伴侣功能是高度受环境温度而调节的：当温度从正常上升到热休克条件时，该蛋白质的分子伴侣活性被大幅度地增强，使之能够有效地与具有聚集倾向的“客户”蛋白质结合。尽管人们一般都认为，当环境温度从休克条件恢复到正常时，客户蛋白质从小分子热休克蛋白上释放和重折叠依赖于像Hsp70和Hsp100这样的ATP依赖性分子伴侣蛋白的帮助，但小分子热休克蛋白在这样的恢复阶段的行为还没有被研究过。在本文的工作中，我们系统分析了小分子热休克蛋白经历温度从热休克降至正常条件过程中的行为。我们发现，只有在热休克胁迫条件下才具有生物学活性的IbpB蛋白，在胁迫条件被消除后仍旧能够长时间维持其分子伴侣活性。我们的比较研究表明，这样的经过热休克预处理过的 IbpB蛋白与未经历过热休克条件的蛋白之间存在很大的构象上的差异,包括前者在N-和C-末端区域可曲性的明显增强，以及亚基动态分离/重结合的加强。令人惊讶的是，我们发现经历过热休克条件的IbpB蛋白的疏水表面表现出大幅度的减小，表明疏水位点的暴露并非该蛋白发挥分子伴侣活性的唯一决定条件。我们认为，像小分子热休克蛋白这样的“持有性”分子伴侣蛋白的活性的维持对于细胞经历过热休克条件后的有效恢复是重要的。