Discovery of a ‘Quantum Switch’ Controlling Photosynthesis by Scientists

Photosynthesis is an important process that allows plants to use sunlight to convert carbon dioxide into organic compounds. Light-harvesting complex II (LHCII) consists of dye molecules bound to proteins. It alternates between two main roles. Under strong light, excess energy is dissipated as heat through non-photochemical quenching, and under weak light, light is efficiently transferred to the reaction center.

Recent bioengineering research has revealed that faster switching between these functions can improve photosynthetic efficiency. For example, soybean crops showed yield increases of up to 33%. However, the precise atomic-level structural changes in LHCII that cause this control have not been known until now.

The molecular mechanism of NPQ and acidity-induced changes in several key structural factors cause the LHCII trimer to switch between light-harvesting and energy-quenching states.Credit: Institute of Physics

innovative research approach

In the new study, researchers led by Professor Weng Yuxiang from the Institute of Physics, Chinese Academy of Sciences, in collaboration with Professor Gao Jiali’s group from the Shenzhen Bay Institute, combined single-particle cryo-electron microscopy (cryo-EM) research. Using multistate density functional theory (MSDFT) calculations of energy transfer between photosynthetic pigment molecules, we analyzed the dynamic structure of his LHCII at atomic resolution and identified photosynthetic pigment quantum switches for intermolecular energy transfer. Masu.

As part of the study, they developed a series of six cryogenic states, including energy transfer states with LHCII in solution and energy quenching states with laterally confined LHCII in membrane nanodisks under neutral and acidic conditions. reported the EM structure.

Comparing these different structures shows that LHCII undergoes a structural change upon acidification. This change allosterically changes the interpigment distance of the fluorescence quenching locus lutein 1 (Lut1)-chlorophyll 612 (Chl612) only when LHCII is confined to membrane nanodiscs, leading to the quenching of excited Chl612 by Lut1. cause. Therefore, lateral pressure-confined LHCII (e.g., aggregated LHCII) is a prerequisite for non-photochemical quenching (NPQ), whereas acidThe induced conformational change enhances fluorescence quenching.

Cryo-EM structures of LHCII in nanodiscs and surfactant solutions at pH 7.8 and 5.4. Credit: Institute of Physics

Quantum switching mechanism in photosynthesis

Through cryo-EM structures and MSDFT calculations of known crystal structures in the extinction state and transient fluorescence experiments, an important quantum switching mechanism of LHCII with the Lut1-Chl612 distance as a key factor was revealed.

This distance controls the energy transfer quantum channels in response to lateral pressure and conformational changes to LHCII. That is, a small change in the critical distance of 5.6 Å allows a reversible switch between light collection and excess energy dissipation. This mechanism allows for rapid response to changes in light intensity, achieving both high efficiency and efficiency. photosynthesis Balanced photoprotection using LHCII as a quantum switch.

Fluorescence decay rate, relationship of Lut1–Chl612 electronic bond strength to Lut1–Chl612 separation distance, and plot of Lut1–Chl612 distance versus crossing angle of TM helices A and B in different LHCII structures. Credit: Institute of Physics

Previously, these two research groups collaborated on molecular dynamics simulations and ultrafast infrared spectroscopy experiments to propose that LHCII is an allosterically controlled molecular machine. Their current experimental cryo-EM structure confirms previously theoretically predicted structural changes in his LHCII.

Reference: “Cryo-EM structure of LHCII in photoactive and photoprotected states reveals allosteric control of light harvesting and excess energy dissipation” Meixia Ruan, Hao Li, Ying Zhang, Ruoqi Zhao, Jun Zhang, Yingjie Wang , Jiali Gao, Zhuan Wang, Yumei Wang, Dapeng Sun, Wei Ding, Yuxiang Weng, August 31, 2023, natural plants.
DOI: 10.1038/s41477-023-01500-2

This research was supported by a project of the Chinese Academy of Sciences, the National Natural Science Foundation of China, and the Shenzhen Science and Technology Innovation Committee.