Atomic force microscopic analysis of the light-harvesting complex 2 from purple photosynthetic bacterium Thermochromatium tepidum
Atomic force microscopic analysis of the light-harvesting complex 2 from purple photosynthetic bacterium Thermochromatium tepidum
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DOI：
10.1007/s11120-023-01010-4
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发表时间：
2023-03-17
影响因子：
3.7
通讯作者：
Saga，Yoshitaka
中科院分区：
文献类型：
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作者：
Morimoto，Masayuki;Hirao，Haruna;Saga，Yoshitaka
紫色光合细菌天线蛋白中重复色素多肽亚基环状排列的结构信息，为更好地理解这种天线的环状结构形成和高效光收集的分子机制提供了线索。本文利用原子力显微镜分析了嗜热紫色细菌热致变色菌（thermochromatium tepidum, tepidum-LH2）的捕光配合物2 （LH2）的环结构。在脂质双分子层中成功地观察到二氢- lh2亚基的圆形排列。环形结构的平均顶距为4.8±0.3 nm，与环形尺寸相关。该值接近于前人分析得出的molischianum（molischianum-LH2）八聚体LH2的顶顶距离。对tepidum- lh2环状结构中相邻亚基组成的片段的角度进行高斯分布，其中值为44°，对应于八角圆结构的角度（45°）。这些结果表明，tepidum- lh2具有由8个重复亚基组成的环状结构。tepidum- lh2与molischianum- lh2的八聚环结构一致，这与tepidum- lh2与molischianum- lh2之间多肽氨基酸序列的同源性一致。
Structural information on the circular arrangements of repeating pigment–polypeptide subunits in antenna proteins of purple photosynthetic bacteria is a clue to a better understanding of molecular mechanisms for the ring-structure formation and efficient light harvesting of such antennas. Here, we have analyzed the ring structure of light-harvesting complex 2 (LH2) from the thermophilic purple bacteriumThermochromatium tepidum(tepidum-LH2) by atomic force microscopy. The circular arrangement of thetepidum-LH2 subunits was successfully visualized in a lipid bilayer. The average top-to-top distance of the ring structure, which is correlated with the ring size, was 4.8 ± 0.3 nm. This value was close to the top-to-top distance of the octameric LH2 fromPhaeospirillum molischianum(molischianum-LH2) by the previous analysis. Gaussian distribution of the angles of the segments consisting of neighboring subunits in the ring structures oftepidum-LH2 yielded a median of 44°, which corresponds to the angle for the octameric circular arrangement (45°). These results indicate thattepidum-LH2 has a ring structure consisting of eight repeating subunits. The coincidence of an octameric ring structure oftepidum-LH2 with that ofmolischianum-LH2 is consistent with the homology of amino acid sequences of the polypeptides betweentepidum-LH2 andmolischianum-LH2.