Zhang Botao, Xu Yuancong, Liu Shuwen, Chen Sixu, Zhao Wencong, Li Zhaoyang, Wang Junshuai, Zhao Weijian, Zhang Heng, Dong Yuhui, Gong Yong, Sheng Wang, Cao Peng
College of Chemistry and Life Science, Beijing University of Technology, Beijing 100124, China.
Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
Int J Mol Sci. 2025 Jan 19;26(2):824. doi: 10.3390/ijms26020824.
Cyanobacterial cytochrome c6 (Cyt c6) is crucial for electron transfer between the cytochrome b6f complex and photosystem I (PSI), playing a key role in photosynthesis and enhancing adaptation to extreme environments. This study investigates the high-resolution crystal structures of Cyt c6 from PCC 7942 and PCC 6803, focusing on its dimerization mechanisms and functional implications for photosynthesis. Cyt c6 was expressed in using a dual-plasmid co-expression system and characterized in both oxidized and reduced states. X-ray crystallography revealed three distinct crystal forms, with asymmetric units containing 2, 4, or 12 molecules, all of which consist of repeating dimeric structures. Structural comparisons across species indicated that dimerization predominantly occurs through hydrophobic interactions within a conserved motif around the heme crevice, despite notable variations in dimer positioning. We propose that the dimerization of Cyt c6 enhances structural stability, optimizes electron transfer kinetics, and protects the protein from oxidative damage. Furthermore, we used AlphaFold3 to predict the structure of the PSI-Cyt c6 complex, revealing specific interactions that may facilitate efficient electron transfer. These findings provide new insights into the functional role of Cyt c6 dimerization and its contribution to improving cyanobacterial photosynthetic electron transport.
蓝藻细胞色素c6（Cyt c6）对于细胞色素b6f复合体与光系统I（PSI）之间的电子传递至关重要，在光合作用中起关键作用，并增强对极端环境的适应性。本研究调查了来自集胞藻PCC 7942和集胞藻PCC 6803的Cyt c6的高分辨率晶体结构，重点关注其二聚化机制及其对光合作用的功能影响。Cyt c6通过双质粒共表达系统在[具体表达宿主未给出]中表达，并对氧化态和还原态进行了表征。X射线晶体学揭示了三种不同的晶体形式，不对称单元包含2、4或12个分子，所有这些都由重复的二聚体结构组成。跨物种的结构比较表明，尽管二聚体定位存在显著差异，但二聚化主要通过血红素裂隙周围保守基序内的疏水相互作用发生。我们提出，Cyt c6的二聚化增强了结构稳定性，优化了电子转移动力学，并保护蛋白质免受氧化损伤。此外，我们使用AlphaFold3预测了PSI-Cyt c6复合体的结构，揭示了可能促进有效电子传递的特定相互作用。这些发现为Cyt c6二聚化的功能作用及其对改善蓝藻光合电子传递的贡献提供了新的见解。
