A group of researchers from Ritsumeikan University, Nagoya University, and Osaka University revealed that principle structures involved in photochemical energy conversion apparatuses are common. The pigment-associated photosynthetic protein, photosystem I (PS I), in higher plants and algae produces highly reducing power (NADPH) which is needed for carbon dioxide fixation, using solar energy. This PS I is known to have evolved from the photosynthetic apparatus in green sulfur bacteria which appeared 3 billion years ago. A special pair of chlorophylls is essential for the initial charge separation reaction in order to produce highly reducing power. Local protein structures, which surround the special pair, have to be kept without great changes in the long evolutionary history of photosynthesis during 3 billion years.

The research group also succeeded in making mutant proteins in green sulfur bacteria with a novel genetic modification technique, although their structural analyses have not been progressed so far.

Figure : The 3D structure of photosystem I which produces highly reducing power (NADPH) (Left side). The detailed structure around a special pair of chlorophylls, P700, in photosystem I (Right side). Only a one side (PsaA side) ligating with the special pair is shown. The amino acid residues, Phe676, His680, Thr742 and Thr743, in photosystem I were predicted to correspond to PscA-Leu617, -His621, -Leu688 and -Val689, respectively, in the photosynthetic apparatus of green sulfur bacteria, based on sequence comparison with each other. Mutations of PscA-Leu688 and -Val689 to cysteine residues induced the S-H stretching vibration band and the band shift of keto C=O in a chlorophyll molecule, strongly indicating very similar environments to those in photosystem I.

(Link) http://resou.osaka-u.ac.jp/en/research/2016/20160125_1