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Thermochromatium(Tch.)tepidum是一种中等嗜热的紫色光合细菌,最佳生长温度为48-50℃;其捕光天线复合物2(LH2)含有非均一性脱辅基蛋白和类胡萝卜素(Car),且高分辨率晶体结构未知.我们通过超快光谱研究了分别采用去垢剂n-dodecyl-β-D-maltoside(DDM)和lauryldimethylamine oxide(LDAO)制备的LH2的激发态动力学,观测到由细菌叶绿素(BChl)的Qy态介导的B800-to-B850单重态能量传递过程(时间尺度～1.2ps,用DDM制备的LH2),以及由类胡萝卜素S2态介导的Car-to-Car和Car-to-BChl单重态能量传递过程(～100fs).结果表明C=C共轭双键数目(NC=C)为11和12的两类Car共处于同一LH2复合物中;相对于源自其它菌种、构成组分相对简单的LH2,Tch.tepidum的LH2中B800-B850的相对取向有较大差异.本工作发现LH2中低含量类胡萝卜素组分anhydrorhodovibrin(NC=C=12)起着高效“能量陷阱”的作用,可能是一种重要的光保护机制;基于类胡萝卜素的超快谱带位移现象提出(OH-)spirilloxanthin(NC=C=13)距BChl分子可能比其它类胡萝卜素更近.这些研究结果有助于进一步理解苛刻自然条件下生长的Tch.tepidum的捕光和光保护机制.
Thermochromatium (Tch.) Tepidum is a moderately thermophilic purple photosynthetic bacterium with an optimal growth temperature of 48-50 ° C; its light harvesting antenna complex 2 (LH2) contains heterogeneous apo-proteins and carotenoids Car), and the high-resolution crystal structure is unknown.We investigated the excited state kinetics of LH2 prepared by using detergent n-dodecyl-β-D-maltoside (DDM) and lauryldimethylamine oxide (LDAO) The B800-to-B850 singlet energy transfer mediated by the Qy state of bacterial chlorophyll (BChl) was observed (time scale ~ 1.2 ps, LH2 prepared with DDM) and the carotenoid S2-mediated Car -to-Car and Car-to-BChl singlet energy transfer processes (-100 fs). The results show that two types of Car with C = C conjugate double bonds (NC = C) of 11 and 12 are co-located in the same LH2 complex In contrast, the relative orientation of B800-B850 in LH2 of Tch.tepidum was significantly different from that of LH2 in other species.It was found that low-content carotenoid LH2 in anhydrohodovibrin (NC = C = 12) plays an efficient “energy trap” role and may be an important photoprotective mechanism; based on the carotenoid The fast band shift phenomenon suggests that (OH-) spirilloxanthin (NC = C = 13) may be closer to the BChl molecule than other carotenoids.These findings are useful for further understanding of the light harvesting of Tch.tepidum grown under harsh natural conditions And light protection mechanism.