CAJ | 학술논문

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～1.2 ps,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(～100 fs).结果表明C=C共轭舣键数目(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.)tepidum시일충중등기열적자색광합세균,최가생장온도위48-50℃;기포광천선복합물2(LH2)함유비균일성탈보기단백화류호라복소(Car),차고분변솔정체결구미지.아문통과초쾌광보연구료분별채용거구제,n-dodecyl-β-D-maltoside(DDM)화lauryldimethylamine oxide(LDAO)제비적LH2적격발태동역학,관측도유세균협록소(BChl)적Qy태개도적B800-to-B850단중태능량전체과정(시간척도～1.2 ps,용DDM제비적LH2),이급유류호라복소S2태개도적Car-to-Car화Car-to-BChl단중태능량전체과정(～100 fs).결과표명C=C공액의건수목(Nc=c)위11화12적량류Car공처우동일LH2복합물중;상대우원자기타균충、구성조분상대간단적LH2,Tch.tepidum적LH2중B800-B850적상대취향유교대차이.본공작발현LH2중저함량류호라복소조분anhydrorhodovibrin(Nc=c=12)기착고효"능량함정"적작용,가능시일충중요적광보호궤제;기우류호라복소적초쾌보대위이현상제출(OH-)spirilloxanthin(Nc=c=13)거BChl분자가능비기타류호라복소경근.저사연구결과유조우진일보리해가각자연조건하생장적Tch.tepidum적포광화광보호궤제.
Purple photosynthetic bacterium Thermochromatium (Tch.) tepidum is a moderate thermophile growing in an optimal temperature range of 48-50℃.Its light-harvesting complex 2 (LH2) possesses heterogeneous compositions of apoprotein and carotenoid (Car),but the high-resolution crystallographic structure remains unknown.We have attempted an ultrafast time-resolved spectroscopic study of the isolated LH2 complex from Tch.tepidum.The spectral dynamics and population kinetics of n-dodecyl-β-D-moltoside (DDM) and lauryldimethylamine oxide (LDAO)preparations of LH2 reveal efficient S2-state mediated Car-to-Car and Car-to-bacteriochlorophyll (BChl) singlet excitation energy transfer (EET) occurring in a time scale of～100 fs,as well as the Qy-state mediated B800-to-B850 singlet EET for the DDM preparation proceeding with a time constant of～1.2 ps.These ultrafast EET processes suggest that the Cars with 11 and 12 conjugated C=C double bonds (Nc=c) coexist in the LH2 complex,and that the B800-B850 mutual orientation in LH2 differs considerably from those in the LH2s from some of the previously investigated bacterial species.In addition,anhydrorhodovibrin (Nc=c=12) as a minor Car composition is found to act as an efficient trap of excitation energy,which is considered to be an important photoprotection mechanism.Furthermore,based on the results of ultrafast Car band shift in response to BChl excitation,we propose that,compared to other Car compositions,(OH-)spirilloxanthin (Nc=c=13) locates in closer proximity to BChl.Our results may facilitate to understand the light-harvesting and the photoprotection mechanisms of Tch.tepidum living under harsh natural conditions.