Onoa Bibiana, Fukuda Shingo, Iwai Masakazu, Bustamante Carlos, Niyogi Krishna K
Howard Hughes Medical Institute, University of California, Berkeley, California.
Howard Hughes Medical Institute, University of California, Berkeley, California.
Biophys J. 2020 Apr 21;118(8):1876-1886. doi: 10.1016/j.bpj.2020.02.029. Epub 2020 Mar 13.
Thylakoid membranes in chloroplasts contain photosynthetic protein complexes that convert light energy into chemical energy. Photosynthetic protein complexes are considered to undergo structural reorganization to maintain the efficiency of photochemical reactions. A detailed description of the mobility of photosynthetic complexes in real time is necessary to understand how macromolecular organization of the membrane is altered by environmental fluctuations. Here, we used high-speed atomic force microscopy to visualize and characterize the in situ mobility of individual protein complexes in grana thylakoid membranes isolated from Spinacia oleracea. Our observations reveal that these membranes can harbor complexes with at least two distinctive classes of mobility. A large fraction of grana membranes contained proteins with quasistatic mobility exhibiting molecular displacements smaller than 10 nm. In the remaining fraction, the protein mobility is variable with molecular displacements of up to 100 nm. This visualization at high spatiotemporal resolution enabled us to estimate an average diffusion coefficient of ∼1 nm s. Interestingly, both confined and Brownian diffusion models could describe the protein mobility of the second group of membranes. We also provide the first direct evidence, to our knowledge, of rotational diffusion of photosynthetic complexes. The rotational diffusion of photosynthetic complexes could be an adaptive response to the high protein density in the membrane to guarantee the efficiency of electron transfer reactions. This characterization of the mobility of individual photosynthetic complexes in grana membranes establishes a foundation that could be adapted to study the dynamics of the complexes inside intact and photosynthetically functional thylakoid membranes to be able to understand its structural responses to diverse environmental fluctuations.
叶绿体中的类囊体膜含有将光能转化为化学能的光合蛋白复合物。光合蛋白复合物被认为会进行结构重组以维持光化学反应的效率。为了理解膜的大分子组织是如何因环境波动而改变的，有必要对光合复合物的迁移率进行实时详细描述。在这里，我们使用高速原子力显微镜来可视化和表征从菠菜中分离出的基粒类囊体膜中单个蛋白复合物的原位迁移率。我们的观察结果表明，这些膜可以容纳至少两类具有不同迁移率的复合物。很大一部分基粒膜含有迁移率为准静态的蛋白质，其分子位移小于10纳米。在其余部分中，蛋白质迁移率是可变的，分子位移可达100纳米。这种高时空分辨率的可视化使我们能够估计平均扩散系数约为1纳米/秒。有趣的是，受限扩散模型和布朗扩散模型都可以描述第二组膜的蛋白质迁移率。据我们所知，我们还提供了光合复合物旋转扩散的首个直接证据。光合复合物的旋转扩散可能是对膜中高蛋白密度的一种适应性反应，以保证电子传递反应的效率。对基粒膜中单个光合复合物迁移率的这种表征奠定了一个基础，该基础可用于研究完整且具有光合功能的类囊体膜内复合物的动态，从而能够理解其对各种环境波动的结构响应。
