We have shown that cyanobacterial chaperonins have pH-dependent anti-aggregation activity. The pH in cyanobacterial cytosol increases by one pH unit following a shift from darkness to light. In the present study, we examined whether other major chaperones such as Hsp90 (HtpG) and Hsp70 (DnaK2) from the cyanobacterium Synechococcus elongatus PCC7942 also display pH-dependent activity. Suppressing aggregation of various heat-denatured proteins, especially lactate dehydrogenase, at an equimolar ratio of cyanobacterial Hsp90 to protein substrate was found to be pH-dependent. Hsp90 showed the highest activity at pH 8.5 over the examined pH range of 7.0 to 8.5. pH affected the anti-aggregation activity of DnaK2 in a similar manner to that of Hsp90 in the presence of half equimolar DnaK2 to the protein substrate. The ATPase activity of cyanobacterial Hsp90 was pH-dependent, with a four-fold increase in activity when the pH was raised from 7.0 to 8.5. The ATPase activity of DnaK2 was also regulated by pH in a similar manner. Finally, an increase in pH from 7.0 to 8.5 enhanced activities of both Hsp90 and Hsp70 in protein-folding assistance by two- to three-fold. These results suggest that changes in pH may regulate chaperone function during a light-dark cycle in cyanobacterial cells.

中文翻译：

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蓝藻 Hsp90 和 Hsp70 的 pH 调节伴侣功能：对光/暗调节的影响

我们已经证明蓝藻伴侣蛋白具有依赖于 pH 值的抗聚集活性。在从黑暗到​​光明的转变之后，蓝藻细胞质中的 pH 值增加一个 pH 单位。在本研究中，我们检查了其他主要分子伴侣，如来自细长蓝藻聚球藻的Hsp90 (HtpG) 和 Hsp70 (DnaK2)PCC7942 还显示出 pH 依赖性活性。发现在蓝藻 Hsp90 与蛋白质底物的等摩尔比下抑制各种热变性蛋白质（尤其是乳酸脱氢酶）的聚集是 pH 依赖性的。在 7.0 至 8.5 的检测 pH 范围内，Hsp90 在 pH 8.5 下显示出最高活性。在存在与蛋白质底物半等摩尔的 DnaK2 的情况下，pH 值以与 Hsp90 相似的方式影响 DnaK2 的抗聚集活性。蓝藻 Hsp90 的 ATPase 活性是 pH 依赖性的，当 pH 从 7.0 升高到 8.5 时，其活性增加了四倍。DnaK2 的 ATPase 活性也以类似的方式受 pH 调节。最后，pH 从 7.0 增加到 8.5 将 Hsp90 和 Hsp70 在蛋白质折叠辅助方面的活性提高了两到三倍。