Abstract of Doctoral Thesis
Title ： Supramolecular Nanostructures of Chlorosomal Chlorophyll Self-Aggregates
Doctoral Program in Advanced Life Sciences Graduate School of Life Sciences
Ritsumeikan University
ふりがな すなお しょうじ 氏 名 Sunao Shoji
Photosynthetic light-harvesting (LH) antennas have attracted much attention from the viewpoint of their supramolecular structures and functions. LH antennas contain bacteriochlorophyll [(B)Chl]
pigments which are the most important porphyrinoids in nature and play key roles in primary processes of photosynthesis including sunlight absorption, excited energy migration/transfer and charge separation. Most (B)Chl pigments are located in a specific array by binding with peptides.
Major antenna systems in green photosynthetic bacteria are called chlorosomes. In a chlorosome, a large amount of BChl-c/d/e/f molecules form J-type self-aggregates without any assistance from the peptides in a hydrophobic environment constructed by lipid monolayer. Their supramolecular nanostructure is supposed to be a tube with a 5~10-nm diameter or a lamella sheet. Here, I report supramolecular nanostructures of chlorosomal self-aggregates of synthetic chlorophyll derivatives and naturally occurring BChls.
A self-aggregative zinc chlorophyll derivative possessing a dodecyl chain at the 17-propionate residue was prepared by modifying naturally occurring Chl-a. Its chlorosomal self-aggregates were prepared in 1% (v/v) THF and hexane. The self-aggregates on substrates were analyzed by spectroscopic and microscopic analysis including cryogenic-transmission electron (cryo-TEM), transmission electron (TEM), scanning electron (SEM) and atomic force microscopies (AFM). The microscopic analyses indicated self-aggregates of the zinc chlorophyll derivative were tube-shaped supramolecular nanostructures with a 5-nm diameter. Next, chlorosomal self-aggregates of zinc chlorophyll derivatives possessing an oligomethylene (straight alkyl) chain at the 17-propionate residue were prepared in a hexane-based solution. Their AFM analysis showed a long oligomethylene chain at the 17-propionate residue was useful for formation and stabilization of tube-shaped supramolecular nanostructures with a 5-nm diameter due to its hydrophobic interaction.
Self-aggregates of naturally occurring BChl-c from a green photosynthetic bacterium, Chloroflexus (Cfl.) aurantiacus, were reconstructed in a hexane-based solution. AFM analysis indicated them to be tubes with a 5-nm diameter. Supramolecular nanostructure of such in vitro self-aggregates were identical to that of in vivo self-aggregates of Cfl. aurantiacus.
