圖1. 一項新研究業已揭露一種，在捕獲光的複合體II (LHCII)中，對高效光合作用至關重要的量子轉換機制。該項透過先進之低溫電子顯微鏡術(cryo-EM：Cryogenic electron microscopy)，及理論計算獲得的發現，證實了LHCII在調節植物能量轉移中的動態角色。
A new study has revealed a quantum switching mechanism in Light-harvesting complex II (LHCII), crucial for efficient photosynthesis. This discovery, achieved through advanced cryo-EM and theoretical calculations, confirms LHCII’s dynamic role in regulating energy transfer in plants.
Photosynthesis is a vital process enabling plants to transform carbon dioxide into organic compounds using sunlight. The Light-harvesting complex II (LHCII) consists of pigment molecules attached to proteins.
光合作用是使植物能利用陽光，將二氧化碳轉化成有機化合物的重要過程。捕獲光的複合體II (LHCII)，由附著於蛋白質上的色素分子組成。
It alternates between two primary roles: when under intense light, it dissipates excess energy as heat through nonphotochemical quenching, and under low light, it efficiently transfers light to the reaction center.
它在兩個主要角色間交替：在強光下，它透過非光化學猝滅，以熱量形式消散過多的能量。在弱光下，它有效地將光轉移到反應中心。
Recent bioengineering research has revealed that speeding up the switch between these functions can boost photosynthetic efficiency. For instance, soybean crops have shown yield increases of up to 33%. However, the precise atomic-level structural changes in LHCII that trigger this regulation were previously unknown.
最近的生物工程研究業已揭露，加速於此些功能之間的轉換，能提高光合作用的效率。譬如，大豆作物已經證實，產量增加達33%。然而，於LHCII 中，觸發此調節的精確原子級結構變化，先前是不詳的。
圖2. 非光化學猝滅(NPQ：Non-Photochemical Quenching)之分子機制及在一些關鍵結構因素中，驅動LHCII三聚體，於捕獲光與能量猝滅狀態間切換之酸度誘導的變化。
Molecular mechanism of NPQ and acidity-induced changes in some key structural factors drive the LHCII trimer to switch between light-harvesting and energy-quenching states.
ln a new study, researchers led by Prof. Weng Yuxiang from the Institute of Physics of the Chinese Academy of Sciences, together with Prof. Gao Jiali’s group from Shenzhen Bay Laboratory, combined single-particle cryo-electron microscopy (cryo-EM) studies of dynamic structures of LHCII at atomic resolution with multistate density functional theory (MSDFT) calculations of energy transfer between photosynthetic pigment molecules to identify the photosynthetic pigment quantum switch for intermolecular energy transfer.
在一項新研究中，由中國科學院物理研究所Weng Yuxiang教授領導的研究人員們，連同來自深圳灣實驗室Gao Jiali教授的團隊結合了，LHCII於原子分辨率下，動態結構之單粒子低溫電子顯微鏡術(cryo-EM)的研究，與光合色素分子之間能量轉移之多態性密度泛函理論(MSDFT)的計算。(密度泛函理論是計算原子、分子及固體電子結構的成功理論)
As part of their work, they reported a series of six cryo-EM structures, including the energy transfer state with LHCII in solution and the energy quenching state with laterally confined LHCII in membrane nanodiscs under both neutral and acidic conditions.
作為他們研究的一部分，他們提出了六種低溫電子顯微鏡術的一系列結構報告，包括在溶液中，具有LHCII的能量轉移狀態，及在中性及酸性情況下，於膜奈米盤中，具有遭側向限制之LHCII的能量猝滅狀態。
Comparison of these different structures shows that LHCII undergoes a conformational change upon acidification. This change allosterically alters the inter-pigment distance of the fluorescence quenching locus Lutein1 (Lut1)–Chlorophyll612 (Chl612) only when LHCII is confined in membrane nanodiscs, leading to the quenching of excited Chl612 by Lut1.
此些不同結構的比較顯示，LHCII在酸化時經歷一種構象變化。此變化，僅當LHCII被限制於膜奈米盤(一種合成模型膜的盤狀蛋白質)中時，才變構性地改變螢光猝滅位點，葉黃素1(Lut1)–葉綠素612(Chl612)色素之間的距離。這導致被激發的Chl612遭Lut1猝滅。
Thus, LHCII confined with lateral pressure (e.g., aggregated LHCII) is a prerequisite for non-photochemical quenching (NPQ), whereas acid-induced conformational change enhances fluorescence quenching.
因此，遭側壓限制的LHCII(譬如，聚集的LHCII)是非光化學猝滅(NPQ)的一種先決條件。而酸誘導的構象變化，增強了螢光猝滅。
圖3. LHCII於奈米盤(盤狀蛋白質)及pH 7.8與5.4洗滌劑溶液中之低溫電子顯微鏡術的結構。
Cryo-EM structures for LHCII in nanodisc and in detergent solution at pH 7.8 and 5.4.
Through MSDFT calculations of cryo-EM structures and the known crystal structure in quenched states, together with transient fluorescence experiments, a significant quantum switching mechanism of LHCII has been revealed with Lut1–Chl612 distance as the key factor.
透過低溫電子顯微鏡術的結構及，在猝滅狀態中，已知之晶體結構的多態性密度泛函理論(MSDFT)計算，連同瞬態螢光實驗，以Lut1-Chl612之距離為關鍵因素，已經揭露了LHCII的一種重要量子轉換機制。
This distance regulates the energy transfer quantum channel in response to the lateral pressure on LHCII and the conformational change, that is, a slight change at its critical distance of 5.6 Å would allow reversible switching between light harvesting and excess energy dissipation.
在對LHCII上的側向壓力及構象變化作出反應時，此距離調節了能量轉移量子通道。也就是說，其臨界距離5.6 Å的微小變化能容許，在光捕獲與過量能量耗散之間的可逆切換。
This mechanism enables a rapid response to changes in light intensity, ensuring both high efficiency in photosynthesis and balanced photoprotection with LHCII as a quantum switch.
此機制使能對光強度的變化，作出快速反應。這確保了，在光合作用的高效率，及以LHCII作為量子開關的平衡光保護。
圖4. 於不同LHCII結構中，在螢光衰減率、Lut1-Chl612電子耦合強度對Lut1-Chl612分離距離之間的關係，及Lut1-Chl612距離對跨膜(TM：Transmembrane )螺旋A與B交叉角的圖。
The relationship between fluorescence decay rate, Lut1–Chl612 electronic coupling strength against Lut1–Chl612 separation distance, and plot of Lut1–Chl612 distance versus the crossing angle of TM helices A and B in different LHCII structures.
Previously, these two research groups had collaborated on molecular dynamics simulations and ultrafast infrared spectroscopy experiments and had proposed that LHCII is an allosterically regulated molecular machine. Their current experimental cryo-EM structures confirm the previously theoretically predicted structural changes in LHCII.
先前，這兩支研究團隊曾針對，分子動態模擬及超快紅外光譜學實驗共同進行研究，且曾提出LHCII是一種變構性調節的分子運作物。他們當前實驗之低溫電子顯微鏡術的結構，證實了先前理論上所預測，在LHCII的結構變化。
網址：https://scitechdaily.com/scientists-have-discovered-a-quantum-switch-that-regulates-photosynthesis/
翻譯：許東榮
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