A new joint research, Published in Nature Communications, by scientists from Chinese Academy of Sciences, University of Liverpool, Riken Center for Biosystems Dynamics Research, University of Tokyo provides new insight into the atomic structures and synthesizing mechanisms of key photosynthetic proteins involved in microbial photosynthesis.

Purple bacteria are the oldest microorganisms on Earth that can harness the energy of sunlight through photosynthesis. The central photosynthetic component in purple bacteria is known as a RC-LH1 core supercomplex, which is formed by a light-harvesting 1 ring (LH1) surrounding the reaction center (RC), together with numerous associated pigment molecules such as bacterial chlorophylls and carotenoids.

Using cryo-electron microscopy (cryo-EM) and genetic techniques, the researchers have uncovered key information about the photosynthetic core complex structure of the purple bacterium Rhodobacter sphaeroides.

This study reveals a dimeric RC-LH1 structure and several structural variants in R. sphaeroides. This RC-LH1 core dimer has an "S-shaped" LH1 ring with a large opening, which is formed by two extra protein peptides known as PufX and PufY. By genetically "deleting" these peptides, the researchers deciphered that PufX is responsible for binding two monomeric cores together to form the dimer structure, whereas the PufY peptide sites at the opposite side of the opening is important to keep the "gate".

Based on the systematic study of the dimeric structure and its variants, the researchers propose how the photosynthetic core complex is generated and self-organised in nature.

The researchers further used computational approaches to prove that the "gates" in the "S-shaped" LH1 ring provide the channels for the electron carrier molecules called quinones to diffuse across the LH1 barrier, which is fundamental for efficient photosynthetic electron transport.

In this work, Professor LIU Luning from the University of Liverpool, UK, Professor LI Mei from the Institute of Biophysics, Chinese Academy of Sciences, and Professor Shirouzu from the RIKEN Center for Biosystem Dynamics in Japan are the co-corresponding authors; CAO Peng, Laura Bracun and Atsushi Yamagata are the co-first authors. This work was supported by the Strategic Priority Research Program of CAS, the National Natural Science Foundation of China, the National Key R&D Program of China, the UK Royal Society, and the UK Biotechnology and Biological Sciences Research Council. Data collection and sample analysis were supported and helped by relevant staff such as the Bioimaging Center of the Institute of Biophysics and the Protein Science Research Platform of the Institute of Biophysics.

Figure 1. Cryo-EM structures of RC-LH1 supercomplexes from Rhodobacter sphaeroides

Full text link: https://www.nature.com/articles/s41467-022-29563-3

Contact: LI Mei

Institute of Biophysics, Chinese Academy of Sciences

Beijing 100101, China

Email: meili@ibp.ac.cn

(Reported by Dr. LI Mei's group)