Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel.
Plant J. 2015 Jun;82(5):850-60. doi: 10.1111/tpj.12855.
HSP33 was originally identified in bacteria as a redox-sensitive chaperone that protects unfolded proteins from aggregation. Here, we describe a eukaryote ortholog of HSP33 from the green algae Chlamydomonas reinhardtii, which appears to play a protective role under light-induced oxidizing conditions. The algal HSP33 exhibits chaperone activity, as shown by citrate synthase aggregation assays. Studies from the Jakob laboratory established that activation of the bacterial HSP33 upon its oxidation initiates by the release of pre-bound Zn from the well conserved Zn-binding motif Cys-X-Cys-Xn -Cys-X-X-Cys, and is followed by significant structural changes (Reichmann et al., ). Unlike the bacterial protein, the HSP33 from C. reinhardtii had lost the first cysteine residue of its center, diminishing Zn-binding activity under all conditions. As a result, the algal protein can be easily activated by minor structural changes in response to oxidation and/or excess heat. An attempt to restore the missing first cysteine did not have a major effect on Zn-binding and on the mode of activation. Replacement of all remaining cysteines abolished completely any residual Zn binding, although the chaperone activation was maintained. A phylogenetic analysis of the algal HSP33 showed that it clusters with the cyanobacterial protein, in line with its biochemical localization to the chloroplast. Indeed, expression of the algal HSP33 increases in response to light-induced oxidative stress, which is experienced routinely by photosynthetic organisms. Despite the fact that no ortholog could be found in higher eukaryotes, its abundance in all algal species examined could have a biotechnological relevance.
HSP33 最初在细菌中被鉴定为一种对氧化还原敏感的伴侣蛋白，可防止未折叠的蛋白质聚集。在这里，我们描述了来自绿藻衣藻的 HSP33 的真核生物同源物，它似乎在光诱导的氧化条件下发挥保护作用。藻类 HSP33 表现出伴侣活性，如柠檬酸合酶聚集测定所示。Jakob 实验室的研究表明，细菌 HSP33 在其氧化时的激活是通过从保守的 Zn 结合基序 Cys-X-Cys-Xn -Cys-X-X-Cys 中释放预先结合的 Zn 起始的，随后发生显著的结构变化（Reichmann 等人，）。与细菌蛋白不同，来自 C. reinhardtii 的 HSP33 失去了其中心的第一个半胱氨酸残基，在所有条件下 Zn 结合活性降低。因此，藻类蛋白可以很容易地通过对氧化和/或过热的微小结构变化进行激活。尝试恢复缺失的第一个半胱氨酸对 Zn 结合和激活方式没有重大影响。取代所有剩余的半胱氨酸完全消除了任何残留的 Zn 结合，尽管伴侣激活得以维持。藻类 HSP33 的系统发育分析表明，它与蓝细菌蛋白聚类一致，与其生化定位到叶绿体一致。事实上，藻类 HSP33 的表达会响应光诱导的氧化应激而增加，这是光合作用生物经常经历的。尽管在高等真核生物中没有找到同源物，但它在所有检查的藻类物种中的丰富度可能具有生物技术相关性。
