Life science
Biofuel, Biobattery, Algal engineering

Structural study and structure-based engineering of photosynthetic
electron transfer in cyanobacteria
Institute for Protein ResearchProfessor Genji Kurisu

https://researchmap.jp/read0051718?lang=en

Assistant Professor Akihiro Kawamoto

https://researchmap.jp/akikawa019?lang=en

Life science

Abstract
Photosynthetic electron transfer is a chemical reaction driven by
light energy. The conversion from light energy to chemical energy
is carried out by membrane protein complexes called photosystem
I and II. The structure of the photosystem I complex from thermophilic cyanobacterium in its monomeric state was analyzed at highresolution, and a detailed mechanistic model was proposed toexplain why the complex is monomerized and how the chlorophyllmolecules in the complex enable the characteristic light absorption
and drive the electron transfer.

▍ Background & Results
Plants and algae have changed the ancient Earth into a green
planet by evolving photosynthetic functions, and they continue
to support global environment on which our human societies fully
depend. Photosynthetic reactions are like solar cells that generate
electricity using light energy. The heart of this reaction is the generation of molecular oxygen by oxidizing water using excitationenergy collected by light-harvesting antenna proteins composed ofchlorophyll, as well as of reducing equivalent to fix carbon dioxide.
The understanding and enhancement of photosynthetic function
is an important research topic for the plant science, to stop global
warming or climate change caused by fossil fuel consumption. If
the detailed mechanisms of photosynthetic energy conversion,
which are equivalent to solar cells, can be clarified, it would bepossible to dramatically improve the photosynthetic functions ofplants and algae by engineering the corresponding proteins, which
had been thought to be impossible so far. Our group succeeded in
obtaining a homogeneous membrane protein sample by improving
the purification method of photosystem I in its monomeric state andanalyzed successfully its three-dimensional structure of the complex at atomic resolution by high-quality cryo-electron micrographs
using a state-of-the-art cryo-EM system (Cryo-ARM) (Figure).

Cryo-EM structure of monomeric photosystem I from thermophilic cyanobacterium T. elongatus BP-1

▍ Significance of the research and Future perspective
Our obtained resolution is good enough to discuss the atomic
structure of proteins, pigments, and bound lipids, although themolecular size of photosystem I is larger than those of average
protein molecules. In this analysis, comparison with the sample in
the trimeric state allowed us to identify a cluster of red chlorophylls,
whose absorption spectrum is red-shifted, and to understand how
the bound chlorophyll molecules efficiently utilize the absorbed
light energy. This might help to optimize the artificial photosynthesis and enhancement of photosynthetic functions.
Chlorophyll molecules in the PSI structure with density map

P a t e n t
Orkun; Frank, Anna; Tanaka, Hidaki et al. Cryo-EM structure of a functional monomeric Photosystem I from Thermosynechococcus elongatus
T r e a t i s e Çoruh,reveals red chlorophyll cluster. Commun. Biol., 2021, 4, p.304, doi: 10.1038/s42003-021-01808-9
UR
L http://www.protein.osaka-u.ac.jp/crystallography/LabHP/en/
K e y w o r d membrane protein complex, energy transduction in photosynthesis, cryo-electron microscopy