Dipartimento di Biotecnologie, Università di Verona, Verona, Italy.
Nat Plants. 2020 Mar;6(3):303-313. doi: 10.1038/s41477-020-0612-8. Epub 2020 Mar 9.
Non-photochemical quenching is the photoprotective heat dissipation of chlorophyll-excited states. In higher plants, two quenching sites are located in trimeric LHCII and monomeric CP29 proteins. Catalysis of dissipative reactions requires interactions between chromophores, either carotenoid, chlorophyll or both. We identified CP29 protein domains involved in quenching by complementing an Arabidopsis deletion mutant with sequences deleted in pigment-binding or pH-sensitive sites. Acidic residues exposed to the thylakoid lumen were found not essential for activation of thermal dissipation in vivo. Chlorophylls a603 (a5) and a616 were identified as components of the catalytic pigment cluster responsible for quenching reaction(s), in addition to xanthophyll L2 and chlorophyll a609 (b5). We suggest that a conformational change induced by acidification in PsbS is transduced to CP29, thus bringing chlorophylls a603, a609 and a616 into close contact and activating a dissipative channel. Consistently, mutations on putative protonatable residues, exposed to the thylakoid lumen and previously suggested to regulate xanthophyll exchange at binding site L2, did not affect quenching efficiency.
非光化学猝灭是叶绿素激发态的光保护热耗散。在高等植物中，有两个猝灭位点位于三聚体 LHCII 和单体 CP29 蛋白中。耗散反应的催化需要发色团之间的相互作用，无论是类胡萝卜素、叶绿素还是两者兼有。我们通过用缺失色素结合或 pH 敏感位点的序列互补拟南芥缺失突变体来鉴定参与猝灭的 CP29 蛋白结构域。暴露在类囊体腔中的酸性残基对于体内热耗散的激活不是必需的。叶绿素 a603(a5)和 a616 被鉴定为负责猝灭反应的催化色素簇的组成部分，除了叶黄素 L2 和叶绿素 a609(b5)。我们提出，由 PsbS 酸化诱导的构象变化被传递到 CP29，从而使叶绿素 a603、a609 和 a616 紧密接触并激活耗散通道。一致地，先前被认为调节结合位点 L2 上叶黄素交换的暴露在类囊体腔中的假定可质子化残基的突变，不影响猝灭效率。
