Graduate School of Environmental Science, Hokkaido University, N10 W5, Sapporo, 060-0810, Japan; Institute of Low Temperature Science, Hokkaido University, N19 W8, Sapporo, 060-0819, Japan.
Institute of Low Temperature Science, Hokkaido University, N19 W8, Sapporo, 060-0819, Japan.
Plant Physiol Biochem. 2024 Oct;215:109073. doi: 10.1016/j.plaphy.2024.109073. Epub 2024 Aug 23.
Chlorophyll a serves as a photosynthetic pigment in plants. Its degradation is initiated by the extraction of the central Mg by the Mg-dechelatase enzyme, which is encoded by Stay-Green (SGR). Plant SGR is believed to be derived from bacterial SGR homolog obtained through horizontal gene transfer into photosynthetic eukaryotes. However, it is not known how the bacterial SGR homolog was modified to function in plants. To assess its adaptation mechanism in plants, a bacterial SGR homolog derived from the Anaerolineae bacterium SM23_63 was introduced into plants. It was found that the bacterial SGR homolog metabolized chlorophyll in plants. However, its chlorophyll catabolic activity was lower than that of plant SGR. Recombinant proteins of the bacterial SGR homolog exhibited higher activity than those of the plant SGR. The reduced chlorophyll catabolic activity of bacterial SGR homologs in plants may be associated with low hydrophobicity of the entrance to the catalytic site compared to that of plant SGR. This hinders the enzyme access to chlorophyll, which is localized in hydrophobic environments. This study offers insights into the molecular changes underlying the optimization of enzyme function.
叶绿素 a 是植物光合作用中的色素。其降解是由 Mg 去螯合酶（由 Stay-Green 基因编码）提取中央的 Mg 启动的。植物 SGR 被认为是通过水平基因转移从细菌 SGR 同源物获得的，然后进入光合真核生物。然而，目前尚不清楚细菌 SGR 同源物是如何被修饰以在植物中发挥作用的。为了评估其在植物中的适应机制，将源自 Anaerolineae 细菌 SM23_63 的细菌 SGR 同源物引入植物中。结果发现，细菌 SGR 同源物在植物中代谢叶绿素。然而，其叶绿素分解代谢活性低于植物 SGR。重组细菌 SGR 同源物的蛋白质表现出比植物 SGR 更高的活性。与植物 SGR 相比，细菌 SGR 同源物在植物中的较低的叶绿素分解代谢活性可能与催化部位入口的低疏水性有关。这阻碍了酶与位于疏水环境中的叶绿素的接触。本研究为阐明酶功能优化的分子变化提供了线索。
