Xu Pengqi, Tian Lijin, Kloz Miroslav, Croce Roberta
Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam and LaserLab Amsterdam. De Boelelaan, 1081, 1081 HV, Amsterdam, The Netherlands.
Sci Rep. 2015 Sep 1;5:13679. doi: 10.1038/srep13679.
Photosynthetic organisms protect themselves from high-light stress by dissipating excess absorbed energy as heat in a process called non-photochemical quenching (NPQ). Zeaxanthin is essential for the full development of NPQ, but its role remains debated. The main discussion revolves around two points: where does zeaxanthin bind and does it quench? To answer these questions we have followed the zeaxanthin-dependent quenching from leaves to individual complexes, including supercomplexes. We show that small amounts of zeaxanthin are associated with the complexes, but in contrast to what is generally believed, zeaxanthin binding per se does not cause conformational changes in the complexes and does not induce quenching, not even at low pH. We show that in NPQ conditions zeaxanthin does not exchange for violaxanthin in the internal binding sites of the antennas but is located at the periphery of the complexes. These results together with the observation that the zeaxanthin-dependent quenching is active in isolated membranes, but not in functional supercomplexes, suggests that zeaxanthin is acting in between the complexes, helping to create/participating in a variety of quenching sites. This can explain why none of the antennas appears to be essential for NPQ and the multiple quenching mechanisms that have been observed in plants.
光合生物通过在一个称为非光化学猝灭（NPQ）的过程中将过量吸收的能量以热的形式耗散，从而保护自身免受高光胁迫。玉米黄质对于NPQ的充分发展至关重要，但其作用仍存在争议。主要讨论围绕两点：玉米黄质结合在哪里以及它是否猝灭？为了回答这些问题，我们追踪了从叶片到单个复合物（包括超级复合物）的玉米黄质依赖性猝灭。我们发现少量的玉米黄质与复合物相关联，但与普遍看法相反，玉米黄质本身的结合不会导致复合物的构象变化，也不会诱导猝灭，即使在低pH值下也是如此。我们表明，在NPQ条件下，玉米黄质不会在天线的内部结合位点与紫黄质交换，而是位于复合物的外围。这些结果以及玉米黄质依赖性猝灭在分离的膜中活跃但在功能性超级复合物中不活跃的观察结果表明，玉米黄质在复合物之间起作用，有助于创建/参与各种猝灭位点。这可以解释为什么没有一个天线似乎对NPQ是必不可少的，以及在植物中观察到的多种猝灭机制。
