Applied Science and Technology Department-BioSolar Lab, Politecnico di Torino, Environment Park, Via Livorno 60, 10144, Torino, Italy.
Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, University of Utrecht, Padualaan 8, 3584 CH, Utrecht, The Netherlands.
Nat Commun. 2020 Mar 13;11(1):1361. doi: 10.1038/s41467-020-15184-1.
Grana are a characteristic feature of higher plants' thylakoid membranes, consisting of stacks of appressed membranes enriched in Photosystem II (PSII) and associated light-harvesting complex II (LHCII) proteins, together forming the PSII-LHCII supercomplex. Grana stacks undergo light-dependent structural changes, mainly by reorganizing the supramolecular structure of PSII-LHCII supercomplexes. LHCII is vital for grana formation, in which also PSII-LHCII supercomplexes are involved. By combining top-down and crosslinking mass spectrometry we uncover the spatial organization of paired PSII-LHCII supercomplexes within thylakoid membranes. The resulting model highlights a basic molecular mechanism whereby plants maintain grana stacking at changing light conditions. This mechanism relies on interactions between stroma-exposed N-terminal loops of LHCII trimers and Lhcb4 subunits facing each other in adjacent membranes. The combination of light-dependent LHCII N-terminal trimming and extensive N-terminal α-acetylation likely affects interactions between pairs of PSII-LHCII supercomplexes across the stromal gap, ultimately mediating membrane folding in grana stacks.
类囊体是高等植物类囊体膜的特征结构，由富含光系统 II（PSII）和相关的光捕获复合物 II（LHCII）蛋白的堆叠的附接膜组成，共同形成 PSII-LHCII 超复合物。类囊体堆叠经历光依赖性结构变化，主要通过重组 PSII-LHCII 超复合物的超分子结构。LHCII 对形成类囊体至关重要，其中也涉及 PSII-LHCII 超复合物。通过自上而下和交联质谱的组合，我们揭示了类囊体膜中配对 PSII-LHCII 超复合物的空间组织。由此产生的模型突出了一种基本的分子机制，植物通过该机制在不断变化的光照条件下维持类囊体堆叠。该机制依赖于 LHCII 三聚体暴露在基质侧的 N 端环与相邻膜中彼此相对的 Lhcb4 亚基之间的相互作用。光依赖性 LHCII N 端修剪和广泛的 N 端 α-乙酰化的组合可能会影响基质间隙中 PSII-LHCII 超复合物对的相互作用，最终介导类囊体堆叠中的膜折叠。
