Purification, characterization and crystallization of the core complex from thermophilic purple sulfur bacterium Thermochromatium tepidum
- 作者：Hiroaki Suzuki ; Yu Hirano ; Yukihiro Kimura ; Shinichi Takaichi ; Masayuki Kobayashi ; Kunio Miki ; Zheng-Yu Wang
- 关键词：Light-harvesting ; Reaction center ; Photosynthesis ; Blue native PAGE ; Circular dichroism ; Magnetic circular dichroism
- 刊名：Biochimica et Biophysica Acta (BBA)/Bioenergetics
- 出版年：2007
- 期刊代码：13_00052728
- 类别：bio
- 出版时间：August 2007
- 卷：1767
- 期：8
- 页码：1057-1063
- 文件大小：388 K
摘要
A light-harvesting-reaction center (LH1-RC) core complex has been highly purified from a thermophilic purple sulfur bacterium, Thermochromatium tepidum. The bacteriochlorophyll (BChl) a molecules in the LH1 exhibit a Qy transition at 914 nm, more than 25 nm red-shift from those of its mesophilic counterparts. The LH1-RC complex was isolated in a monomeric form as confirmed by sucrose density gradient centrifugation, blue native PAGE and size-exclusion chromatography. Four subunits (L, M, H and a tetraheme cytochrome) in RC and two polypeptides (α and β) in LH1 were identified. Spirilloxanthin was determined to be the predominant carotenoid in the core complex. The purified core complex was highly stable, no significant change in the LH1 Qy transition was observed over 10 days of incubation at room temperature in dark. Circular dichroism spectrum of the LH1 complex was characterized by low intensity and nonconservative spectral shape, implying a high symmetry of the large LH1 ring and interaction between the BChl a and carotenoid molecules. A dimeric feature of the BChl a molecules in LH1 was revealed by magnetic circular dichroism spectrum. Crystals of the core complex were obtained which diffracted X-rays to about 10 Å.