Khmelnitskiy Anton, Toporik Hila, Mazor Yuval, Jankowiak Ryszard
Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States.
School of Molecular Sciences and The Biodesign Institute, Arizona State University, Tempe, Arizona 85287, United States.
J Phys Chem B. 2020 Oct 1;124(39):8504-8515. doi: 10.1021/acs.jpcb.0c05201. Epub 2020 Aug 27.
To identify the molecular composition of the low-energy states in cyanobacterial Photosystem I (PSI) of PCC6803, we focus on high-resolution (low-temperature) absorption, emission, resonant, and nonresonant hole-burned spectra obtained for wild-type (WT) PSI and three PSI mutants. In the Red_a mutant, the B33 chlorophyll (Chl) is added to the B31-B32 dimer; in Red_b, histidine 95 (His95) on PsaB (which coordinates Mg in the B7 Chl within the His95-B7-A31-A32-cluster) is replaced with glutamine (Gln), while in the Red_ab mutant, both mutations are made. We show that the C706 state (B31-B32) changes to the C710 state (B31-B32-B33) in both Red_a and Red_ab mutants, while the C707 state in WT (localized on the His95-B7-A31-A32 cluster) is modified to C716 in both Red_b and Red_ab. Excitation energy transfer from C706 to the C714 trap in the WT PSI and Red_b mutant is hampered as reflected by a weak emission at 712 nm. Large electron-phonon coupling strength (exposed via resonant hole-burned spectra) is consistent with a strong mixing of excited states with intermolecular charge transfer states leading to significantly red-shifted emission spectra. We conclude that excitation energy transfer in PSI is controlled by fine-tuning the electronic states of a small number of highly conserved red states. Finally, we show that mutations modify the protein potential energy landscape as revealed by different shapes and shifts of the blue- and red-shifted antiholes.
为了确定集胞藻PCC6803光合系统I（PSI）中低能态的分子组成，我们重点研究了野生型（WT）PSI和三个PSI突变体的高分辨率（低温）吸收光谱、发射光谱、共振光谱和非共振空穴烧蚀光谱。在Red_a突变体中，B33叶绿素（Chl）被添加到B31 - B32二聚体中；在Red_b突变体中，PsaB上的组氨酸95（His95）（其在His95 - B7 - A31 - A32 - 簇内与B7 Chl中的镁配位）被谷氨酰胺（Gln）取代，而在Red_ab突变体中，两种突变都存在。我们发现，在Red_a和Red_ab突变体中，C706态（B31 - B32）转变为C710态（B31 - B32 - B33），而野生型中的C707态（位于His95 - B7 - A31 - A32簇上）在Red_b和Red_ab中都被修饰为C716。野生型PSI和Red_b突变体中从C706到C714陷阱的激发能量转移受到阻碍，这表现为712 nm处的微弱发射。大的电子 - 声子耦合强度（通过共振空穴烧蚀光谱揭示）与激发态与分子间电荷转移态的强烈混合一致，导致发射光谱显著红移。我们得出结论，PSI中的激发能量转移是通过微调少数高度保守的红色态的电子态来控制的。最后，我们表明突变改变了蛋白质势能面，这通过蓝移和红移反空穴的不同形状和位移揭示出来。
