体外组装类胡萝卜素对外周捕光复合体(LH2)能量传递活性的影响

【目的】探求不产氧光合细菌(APB)外周捕光复合体(LH2)中类胡萝卜素(Car)结构和能量传递效率的关系和规律。【方法】通过二苯胺(DPA)抑制Car合成的方法从固氮红细菌134K20中获得部分缺失Car的LH2 (LC-LH2)；采用TLC和HPLC法从3种APB中制备球形烯(SE)、玫红品(RP)和奥氏酮(OK) 3种Car；在含0.1%十二烷基二甲基胺氧化物(LDAO)的10 mmol/L Tris-HCl (pH 8.0)缓冲液中采用超声孵育法分别将这3种Car与LC-LH2体外组装，采用吸收光谱法、拉曼光谱法和荧光光谱法对组装LH2进行结构与功能分析。【结果】制备的部分缺失Car的LH2中，SE缺失率约为64.7%。这3种共轭长度、取代基的极性不同的Car均能与这种部分缺失SE的LH2自组装，Car组装率约在24.0%?29.4%之间，其中SE和OK的组装率高于RP。与部分缺失Car LH2中原有SE构象一致，重组的Car在LH2中也呈现较为伸展的平面构象。LH2中重组Car到细菌叶绿素(BChl)的能量传递效率由高到低的顺序依次为SE-LH2>RP-LH2>OK-LH2，与Car共轭体系大小的关系一致，而与Car极性大小没有明显的关系。【结论】在组装的LH2中Car采用平面构象与脱辅基蛋白结合，Car共轭长度仍是决定和影响LH2中Car-BChl能量传递效率的主要因素，而Car的取代基和极性影响较小。

Reconstitution of carotenoids into peripheral light harvesting complex 2 of Rhodobacter azotoformans in vitro and its effects on energy transfer

[Objective] To explore the relationships between carotenoid (Car) structure and energy transfer efficiency in peripheral light-harvesting complex 2 (LH2) from anoxygenic phototrophic bacteria (APB). [Methods] Partially carotenoid-deficient LH2 (LC-LH2) was obtained from Rhodobacter azotoformans 134K20 by diphenylamine (DPA) inhibition. Three Cars including spheroidene (SE), rhodopin (RP) and okenone (OK) were obtained from three species of APB by thin layer chromatography and high performance liquid chromatography. The reconstitutions of different Cars into LC-LH2 were performed by using ultrasonic procedures in 10 mmol/L Tris-HCl buffer, pH 8.0, containing 0.1% LDAO. The structure and function of reconstituted LH2 (N-LH2) were studied by using UV-VIS spectra, Raman spectra and fluorescence spectroscopy. [Results] The deficiency of SE in LC-LH2 was about 64.7%. Three Cars with different conjugation length, substituent and polarity could be reconstituted into the partially SE-deficient LC-LH2, and the reconstitution efficiency was in the range from 24.0% to 29.4%, and the reconstitution efficiencies of SE and OK were higher than that of RP. Compared to the intrinsic planner conformation of SE in LC-LH2, the incorporated Cars also adopted a planner conformation in N-LH2. The Car to bacteriochlorophyll (BChl) energy transfer efficiency in different N-LH2 changed in the order of SE-LH2>RP-LH2>OK-LH2. The energy transfer efficiency in N-LH2 had a negative correlation with the conjugated length of Cars, whereas independent of the polarity of Cars. [Conclusion] In N-LH2, Cars bind to the apoproteins with a planner conformation, the conjugated length of Cars still plays a dominant role in controlling the Car to BChl energy transfer efficiency; however, the substituent and polarity of Cars have negligible effects on energy transfer efficiency.