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.

非光化学淬灭是叶绿素激发态的光保护散热。在高等植物中，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生色团之间的相互作用，类胡萝卜素，叶绿素或两者。我们通过与拟南芥缺失突变体与色素结合位点或pH敏感位点缺失的序列互补来鉴定与淬灭有关的CP29蛋白结构域。发现暴露于类囊体腔的酸性残基对于体内的散热激活不是必需的。叶绿素a 603（a5）和a除叶黄素L2和叶绿素a 609（b5）之外，还确定616是催化颜料簇中引起淬灭反应的组分。我们建议在PSBS诱导酸化的构象改变转导到CP29，从而把叶绿素一个603，一个609和一个616紧密接触并激活耗散通道。一致地，假定的质子化残基上暴露于类囊体腔的突变，以前建议在结合位点L2调节叶黄素交换，但不影响淬灭效率。