Akter Tahmina, Nakamoto Hitoshi
Department of Biochemistry and Molecular Biology, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan.
J Biochem. 2021 Dec 4;170(4):463-471. doi: 10.1093/jb/mvab061.
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 this study, we examined whether other major chaperones such as Hsp90 (HtpG) and Hsp70 (DnaK2) from the cyanobacterium Synechococcus elongatus PCC 7942 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 fourfold 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 threefold. These results suggest that changes in pH may regulate chaperone function during a light-dark cycle in cyanobacterial cells.
我们已经表明，蓝藻伴侣蛋白具有pH依赖性的抗聚集活性。从黑暗转变为光照后，蓝藻细胞质中的pH值会增加一个pH单位。在本研究中，我们检测了来自聚球藻属PCC 7942的其他主要伴侣蛋白，如Hsp90（HtpG）和Hsp70（DnaK2）是否也具有pH依赖性活性。发现在蓝藻Hsp90与蛋白质底物等摩尔比的情况下，抑制各种热变性蛋白（尤其是乳酸脱氢酶）的聚集具有pH依赖性。在所检测的7.0至8.5的pH范围内，Hsp90在pH 8.5时表现出最高活性。在DnaK2与蛋白质底物为半等摩尔的情况下，pH以与Hsp90类似的方式影响DnaK2的抗聚集活性。蓝藻Hsp90的ATP酶活性具有pH依赖性，当pH从7.0升高到8.5时，活性增加四倍。DnaK2的ATP酶活性也以类似方式受pH调节。最后，pH从7.0升高到8.5使Hsp90和Hsp70在蛋白质折叠辅助方面的活性增强了两到三倍。这些结果表明，pH的变化可能在蓝藻细胞的明暗循环过程中调节伴侣蛋白的功能。
