Noji Tomoyasu, Saito Keisuke, Ishikita Hiroshi
Department of Applied Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo, 1, Japan.
Research Center for Advanced Science and Technology, The University of Tokyo, Meguro-ku, Tokyo, Japan.
Commun Chem. 2024 Aug 30;7(1):192. doi: 10.1038/s42004-024-01281-5.
Structural differences between illuminated and unilluminated crystal structures led to the proposal that the charge-separated state was stabilized by structural changes in its membrane extrinsic protein subunit H in a bacterial photosynthetic reaction center [Katona, G. et al. Nat. Struct. Mol. Biol. 2005, 12, 630-631]. Here, we explored the proposal by titrating all titratable sites and calculating the redox potential (E) values in these crystal structures. Contrary to the expected charge-separated states, E for quinone, E(Q/Q), is even lower in the proposed charge-separated structure than in the ground-state structure. The subunit-H residues, which were proposed to exhibit electron-density changes in the two crystal structures, contribute to an E(Q/Q) difference of only <0.5 mV. Furthermore, the protonation states of the titratable residues in the entire reaction center are practically identical in the two structures. These findings indicate that the proposed structural differences are irrelevant to explaining the significant prolongation of the charge-separated-state lifetime.
光照和未光照晶体结构之间的结构差异，促使人们提出电荷分离态是通过细菌光合反应中心膜外在蛋白亚基H的结构变化而得以稳定的观点[Katona, G.等人，《自然结构与分子生物学》，2005年，第12卷，630 - 631页]。在此，我们通过滴定所有可滴定位点并计算这些晶体结构中的氧化还原电位（E）值来探究这一观点。与预期的电荷分离态相反，在所提出的电荷分离结构中，醌的E值（E(Q/Q)）甚至比基态结构中的更低。在两个晶体结构中被认为会出现电子密度变化的亚基H残基，对E(Q/Q)差异的贡献仅<0.5 mV。此外，整个反应中心中可滴定残基的质子化状态在这两种结构中实际上是相同的。这些发现表明，所提出的结构差异与解释电荷分离态寿命的显著延长无关。
