The unique structure of the photosynthetic complex called Lhcp suggests how photosynthetic systems changed as photosynthetic organisms evolved from water to land
Illustration Credit: Osaka Metropolitan University
Scientific Frontline: "At a Glance" Summary
- Main Discovery: Researchers elucidated the three-dimensional structure and function of Lhcp, a unique light-harvesting complex in the prasinophyte alga Ostreococcus tauri, revealing critical evolutionary differences compared to LHCII in terrestrial plants.
- Methodology: The study utilized cryo-electron microscopy to visualize the protein scaffold of Lhcp and analyzed structural variations in pigment binding and protein loops to determine light absorption and energy transfer mechanisms.
- Key Data: The Lhcp trimer architecture is uniquely stabilized by pigment–pigment and pigment–protein interactions, specifically involving a distinct carotenoid arranged at the subunit interface that enhances absorption of blue-green light.
- Significance: This analysis highlights the molecular adaptations that primitive algae utilized to survive in low-light deep-sea environments and identifies structural shifts necessary for the evolutionary transition of photosynthetic organisms from water to land.
- Future Application: Uncovering the molecular basis for the selection of LHCII over Lhcp could refine our understanding of plant evolution and inform the development of artificial photosynthesis systems optimized for specific light environments.
- Branch of Science: Evolutionary Biology, Structural Biology, and Plant Physiology
Early marine algae adapted their light-harvesting systems for weak blue-green light, suggesting how photosynthesis evolved
Before plants evolved, a vegetative life consisted of primitive green algae living in the sea. Like plants, these algae survived by performing photosynthesis, turning sunlight into energy. However, little light reaches the ocean where algae live; therefore, they evolved specialized organs to grab what little is available.
Among these tiny ocean algae are prasinophytes, which are among the earliest photosynthetic life forms on Earth. Like all photosynthetic organisms, they rely on a pigment–protein complex called LHC to capture sunlight. How efficiently LHC performs photosynthesis in different environments depends on the pigments bound to it.
A research team including Associate Professor Ritsuko Fujii of the Graduate School of Science at Osaka Metropolitan University used cryo-electron microscopy to look at the three-dimensional structure and function of Lhcp, a unique prasinophyte LHC, from the microscopic alga Ostreococcus tauri. The team compared their results to LHCII, which is found in terrestrial plants.
They found that the basic design of the protein scaffold was similar, but there were structural differences in pigment binding and protein loops that affect how Lhcp absorbs light and transfers energy. Unlike the plant’s light-harvesting complex, Lhcp’s trimer architecture is stabilized by both pigment–pigment and pigment–protein interactions, especially involving a unique carotenoid arranged at the interface between subunits.
“The carotenoid stabilizes the structure and improves the efficiency of light adsorption of blue-green light, which is abundant in the deep-sea environment,” Professor Fujii explained.
Their results showed that Lhcp includes structures unique to the algae despite sharing some structural and functional features with LHCII. These similarities and differences may be key changes that enabled plants to leave the oceans and colonize the land.
“Understanding this molecular foundation can be used to uncover why, when, and how land plants selected LHCII over Lhcp during their evolutionary process,” Professor Fujii added. “This may be key to understanding this important evolution event.”
Funding: JSPS KAKENHI Grant Number 23K05721 and 24H02091, Osaka Metropolitan University RESPECT Grant 2022, Grant-in-aid for JSPS Research Fellows Grant Number 23KJ1834, JSPS KAKENHI Grant Number 23H04958, JST CREST Grant Number JPMJCR20E1,Platform Project for Supporting Drug Discovery and Life Science Research (BINDS) from AMED under Grant Number JP23ama121001 and JP23ama121003 and JEOL YOKOGUSHI Research Alliance Laboratories of Osaka University, and Koyanagi Foundation Research Grant
Published in journal: Communications Biology
Authors: Soichiro Seki, Masato Kubota, Nami Yamano, Eunchul Kim, Asako Ishii, Tomoko Miyata, Hideaki Tanaka, Richard J. Cogdell, Jian-Ping Zhang, Keiichi Namba, Genji Kurisu, Jun Minagawa, and Ritsuko Fujii
Source/Credit: Osaka Metropolitan University
Reference Number: ebio020326_01