Analysis of LhcSR3, a protein essential for feedback de-excitation in the green alga Chlamydomonas reinhardtii.
Analysis of LhcSR3, a protein essential for feedback de-excitation in the green alga Chlamydomonas reinhardtii.
复制标题
DOI：
10.1371/journal.pbio.1000577
复制
发表时间：
2011-01-18
期刊：
影响因子：
9.8
通讯作者：
Bassi R
中科院分区：
文献类型：
--
作者：
Bonente G;Ballottari M;Truong TB;Morosinotto T;Ahn TK;Fleming GR;Niyogi KK;Bassi R
为了防止过度光照造成的光损伤，植物使用不同的蛋白质来感知pH值的变化并耗散激发态。然而，在绿色微藻中，LhcSR 3基因产物能够执行pH传感和能量淬灭功能。在光合生物中，过量吸收的光能的反馈耗散平衡了光的收集与代谢能量消耗。该机制防止了由叶绿素（Chl）三重态与O2反应产生的活性氧引起的光损伤。已经发现植物在特定的蛋白质中执行热耗散，结合属于Lhc家族的Chl和类胡萝卜素（汽车），而该过程的触发由PsbS亚基执行，其是内腔pH检测所需的。PsbS在藻类中没有发现，这表明能量依赖性淬灭（QE）机制的重要差异。与这一建议相一致，一种不同的Lhc样基因产物，称为LhcSR 3（以前称为LI 818），已被发现是莱茵衣藻qE所必需的。在这项工作中，我们报告的生产两个重组LhcSR异构体从C。reinhardtii及其生化和光谱特征。我们发现以下内容：（i）LhcSR同种型是Chl a/B-和叶黄素-结合蛋白，与高等植物PsbS相反;（ii）LhcSR 3同种型在强光下积累，是Chl激发态的强猝灭剂，表现出非常快的荧光衰减，寿命低于100 ps，能够耗散来自邻近天线蛋白的激发能量;（iii）LhcSR 3同种型在Car自由基阳离子的瞬时形成中具有高度活性，Car自由基阳离子是一种被提出在热耗散过程中充当淬灭剂的物质。值得注意的是，自由基阳离子信号检测波长对应的车叶黄素，而不是玉米黄质，这意味着后者，主要在植物中，是不是必不可少的;（iv）LhcSR 3是响应于低pH值，触发非光化学淬灭，因为它结合非光化学淬灭抑制剂二环己基碳二亚胺，并增加其能量耗散性能酸化。这是第一次报告的一个孤立的LHC蛋白质组成型活性的能量耗散在其纯化形式，开辟了详细的分子分析的方式。由于其质子化残基和组成性激发能量耗散，这种蛋白质似乎合并pH传感和能量淬灭功能，分别由PsbS和单体Lhcb蛋白在植物中完成。活性氧在光合作用过程中形成，特别是当电子传递在强光下饱和时。非光化学猝灭（NPQ）过程通过将叶绿素的激发态耗散成热量来帮助植物免受过量光照的影响。通过这样做，它防止了三重激发态的形成，否则三重激发态将与分子氧反应形成单线态氧，一种破坏性的活性氧物质。在植物中，NPQ是由PsbS蛋白触发的，PsbS蛋白感知由过量光引起的pH变化，从而触发其他蛋白质的能量淬灭功能。绿色微囊藻C. reinhardtii缺乏PsbS蛋白，NPQ依赖于LhcSR 3蛋白。在这项研究中，我们表明，与PsbS，LhcSR 3不仅结合色素，但也是一个强猝灭叶绿素激发态。LhcSR 3携带可质子化的残基，使其能够感测pH变化。其淬灭活性进一步增强低pH值，这表明这种藻类蛋白融合的pH传感器和激发态淬灭剂到一个单一的基因产物的功能。
To prevent photodamage by excess light, plants use different proteins to sense pH changes and to dissipate excited energy states. In green microalgae, however, the LhcSR3 gene product is able to perform both pH sensing and energy quenching functions. In photosynthetic organisms, feedback dissipation of excess absorbed light energy balances harvesting of light with metabolic energy consumption. This mechanism prevents photodamage caused by reactive oxygen species produced by the reaction of chlorophyll (Chl) triplet states with O2. Plants have been found to perform the heat dissipation in specific proteins, binding Chls and carotenoids (Cars), that belong to the Lhc family, while triggering of the process is performed by the PsbS subunit, needed for lumenal pH detection. PsbS is not found in algae, suggesting important differences in energy-dependent quenching (qE) machinery. Consistent with this suggestion, a different Lhc-like gene product, called LhcSR3 (formerly known as LI818) has been found to be essential for qE in Chlamydomonas reinhardtii. In this work, we report the production of two recombinant LhcSR isoforms from C. reinhardtii and their biochemical and spectroscopic characterization. We found the following: (i) LhcSR isoforms are Chl a/b– and xanthophyll-binding proteins, contrary to higher plant PsbS; (ii) the LhcSR3 isoform, accumulating in high light, is a strong quencher of Chl excited states, exhibiting a very fast fluorescence decay, with lifetimes below 100 ps, capable of dissipating excitation energy from neighbor antenna proteins; (iii) the LhcSR3 isoform is highly active in the transient formation of Car radical cation, a species proposed to act as a quencher in the heat dissipation process. Remarkably, the radical cation signal is detected at wavelengths corresponding to the Car lutein, rather than to zeaxanthin, implying that the latter, predominant in plants, is not essential; (iv) LhcSR3 is responsive to low pH, the trigger of non-photochemical quenching, since it binds the non-photochemical quenching inhibitor dicyclohexylcarbodiimide, and increases its energy dissipation properties upon acidification. This is the first report of an isolated Lhc protein constitutively active in energy dissipation in its purified form, opening the way to detailed molecular analysis. Owing to its protonatable residues and constitutive excitation energy dissipation, this protein appears to merge both pH-sensing and energy-quenching functions, accomplished respectively by PsbS and monomeric Lhcb proteins in plants. Reactive oxygen species are formed during photosynthesis, particularly when electron transport is saturated in high light. The process of non-photochemical quenching (NPQ) helps protect plants against excess light by dissipating the excited states of chlorophyll into heat. By doing so, it prevents the formation of triplet excites that otherwise would react with molecular oxygen to form singlet oxygen, a damaging reactive oxygen species. In plants, NPQ is triggered by the PsbS protein, which senses pH changes caused by excess light and consequently triggers energy-quenching functions in other proteins. The green microalga C. reinhardtii lacks the PsbS proteins, and NPQ depends on the LhcSR3 protein. In this study, we show that, unlike PsbS, LhcSR3 not only binds pigments but is also a strong quencher for chlorophyll excited states. LhcSR3 carries protonatable residues that enable it to sense pH change. Its quenching activity is further enhanced by low pH, suggesting that this algal protein merges the functions of pH sensor and of excited state quencher into a single gene product.
登录
查看更多内容
影响因子：
2.9
作者：
Croce, R;Canino, G;Bassi, R
通讯作者：
Bassi, R
影响因子：
3.5
作者：
Croce, R;Remelli, R;Bassi, R
通讯作者：
Bassi, R
影响因子：
4.8
作者：
BERGANTINO, E;DAINESE, P;BASSI, R
通讯作者：
BASSI, R
影响因子：
2.9
作者：
Castelletti, S;Morosinotto, T;Croce, R
通讯作者：
Croce, R
DOI：
10.1046/j.1432-1033.2001.01874.x
发表时间：
2001-01-01
期刊：
EUROPEAN JOURNAL OF BIOCHEMISTRY
影响因子：
--
作者：
Crimi, M;Dorra, D;Bassi, R
通讯作者：
Bassi, R