Cucumber (Cucumis sativus L.) LHC-Ⅱ complex, which consists of only one subunit (27 kD), was isolated and purified. 2-D crystallization was performed by batch method. The crystal is 0.7 μm×1.0 μm, and diffracts to 30 ?. The projection map of the negatively stained two-dimensional crystal of LHC-Ⅱ complex shows that the crystal has p3 symmetry, lattice constant 15.4 nm×15.4 nm, which is different from the LHC-Ⅱ of spinach (Spinacia oleracea L.) and pea (Pisum satium L.). A continuous tomographic tilt series, containing 12 projections from the two-dimensional crystal was subjected to 3-D reconstruction. The 3-D model represents that LHC-Ⅱ complex consists of 6 monomers. These trimer and dimer interactions build up the sixmember ring.
黄瓜27 kD LHC-II复合物三维结构的电子晶体学初步研究
张旭家1 王凌云1 黄有国1 王可玢2 匡廷云2
（1. 中国科学院生物物理研究所生物大分子国家重点实验室，北京100101；2. 中国科学院植物研究所，北京100093）
摘要：从黄瓜(Cucumis sativus L.)叶片中分离出只含有一种亚基(27 kD)的LHC-Ⅱ复合物.采用batch方法获得了其二维晶体,大小为0.7 μm×1.0μm,衍射能力达30 A.负染样品的二维投影结果表明,该晶体为p3对称性,晶胞参数为15.4 nm×15.4 nm,不同于以往报道的菠菜(Spinacia oleracea L.)或豌豆(Pisum satium L.)LHC-Ⅱ晶体,为另外一种晶型.采用tomography技术,收集了0°～-55°系列倾斜照片,进行三维重构.LHC-Ⅱ复合物是由6个单体组成的六元环,相邻2个单体分别从膜的两侧插膜,方向相反,在膜区靠疏水-疏水相互作用成二聚体,3个相同的二聚体相互连接成六元环.
关键词： LHC-II；电子晶体学；三维重构
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