Investigation of the functional mechanisms of artificial photosynthetic pigment-protein supra-molecular complexes

点击翻译按钮获取中文摘要

Three different kinds of pigment-protein complexes (two antennae called LH2 and LH1, and reaction center (RC)) are deeply involved in the primary process of purple photosynthetic bacteria. In this research project, for the deeper understanding of the functional mechanisms of these pigment-protein complexes, artificial pigment-protein complexes in which the structure of the carotenoid pigments were modified by utilizing organic synthesis were extensively studied. The following remarkable features have been achieved.1.Achievement of the large-scale total synthesis of analogue carotenoids : Larges-scale total syntheses of a series of analogue carotenoids of spheroidene, spirilloxanthin, and lycopene which have different extent of conjugation were achieved.2.X-ray crystallography of the reaction centers in which the analogue carotenoids have been incorporated : The analogue carotenoids of spheroidene were incorporated into the carotenoidless reaction center (RC) from a photosynthetic bacte … More rium Rhodobacter sphaeroides strain R26.1. Thus prepared artificial RCs were crystallized and their crystal structures were determined by X-ray crystallography. These structure analyses revealed the unidirectional insertion of the carotenoid molecule when it is incorporated into the RC. PheM162 is a gate-keeper amino-acid residue, while TrpM75 is a locking amino-acid residue when the carotenoid molecule is re-incorporated into the R26.1 RC.3.Electroabsorption spectroscopy on the native LH2 antenna complex : Electroabsorption spectroscopy using dual-phase lock-in detection was proposed to be one of the most promising methods to detect the electrostatic interaction between the pigments and apoproteins in the pigment-protein complexes. Exact experimental protocols together with the analysis methods were constructed, and they were applied to the native LH2 complex from a photosynthetic bacterium Rb, sphaeroides strain GIC.4.Electroabsorption spectroscopy of the artificial reaction centre in which an analogue carotenoid has been re-incorporated : Electroabsorption spectroscopy was applied to the carotenoidless reaction centre (RC) from Rb. sphaeroides strain R26.1 as well as the same RC in which an analogue carotenoid has been incorporated. We have, for the first time, quantitatively determined the difference of the electrostatic environment induced by the presence or absence of a carotenoid molecule around the bacteriochlorophyll molecules bound to the RC.5.Sub-20 fs time-resolved absorption spectroscopy of carotenoids : Time-resolved absorption spectroscopy with unprecedented temporal resolution of sub-20 fs was applied to f3-carotene and lycopene. The intermediate singlet excited-state (Sx state) in-between the one-photon allowed 1^1B_u^+(S_2) and forbidden 2^1Ag^-(S_1) states was time-resolved for the first time in the real time-domain, and it was evidenced that this intermediate excited state was involved in the relaxation process following the photoexcitation up to the 1^1B_u^+ state. This study was extended to the series of carotene molecules which have different polyene chain-lengths. Except the case of the carotene molecule having 5 conjugated C=C bonds, all the carotene molecules were evidenced in real time-domain to have the S_x state in the relaxation process from S_2 to S_1.6.Reorganization of the LHI antenna complex of Rs. rubrum and its electroabsorption spectroscopy : Carotenoid-free monomeric subunits of B880 pigment-protein complex from Rs. rubrum strain G9+ was reorganized with purified all-trans-spirilloxanthin to form the artificial light-harvesting 1(LH1) complex. Electroabsorption spectroscopy was applied to thus reconstituted LH1 in order to evaluate electrostatic interaction between pigments and apo-proteins in the complex. Less