A team of researchers from Okayama University in Japan has revealed a groundbreaking high-resolution cryo-electron microscopy (cryo-EM) structure of photosystem II (PSII) in the marine alga Chrysotila roscoffensis, a haptophyte species known for its intricate calcium carbonate plates called coccoliths. This discovery sheds new light on the unique molecular architecture of light-harvesting complexes in marine algae, opening promising avenues for advancing artificial photosynthesis technologies. With the global quest for sustainable energy sources intensifying, understanding the nuances of natural photosynthesis at the molecular level provides a crucial blueprint for engineering next-generation solar energy conversion systems.
Photosynthesis is the cornerstone of life on Earth, transforming sunlight into chemical energy and releasing molecular oxygen, which maintains atmospheric balance and sustains diverse ecosystems. Central to this process are the photosystems—complex assemblies of proteins and pigments embedded in the thylakoid membranes of chloroplasts. PSII initiates photosynthesis by harnessing light energy to catalyze the photolysis of water molecules, generating oxygen, protons, and electrons. These electrons then flow to photosystem I (PSI), where they undergo further excitation before enabling carbon fixation. Despite its indispensability, the precise structural adaptations of PSII across different species, particularly marine photosynthetic organisms like haptophytes, have remained elusive due to their complex protein-pigment interactions.
The research led by Assistant Professor Romain La Rocca, alongside Associate Professor Fusamichi Akita and Professor Jian-Ren Shen, utilized cryo-EM at an exceptional 2.2-angstrom resolution to unravel the detailed configuration of the PSII-FCPII (fucoxanthin chlorophyll c-binding protein) supercomplex in Chrysotila roscoffensis. This imaging breakthrough has elucidated the spatial arrangement of six FCPII antenna proteins per PSII monomer, revealing a distinct organizational pattern markedly different from that observed in diatoms and green algae. These findings underscore the evolutionary adaptations these marine algae have developed to optimize light capture and energy transfer in their specific ecological niches within the ocean surface layers.
One of the most striking revelations of the study is the identification of the FCPII-2 antenna protein as a central energy hub within the PSII supercomplex. This protein occupies a strategic position, efficiently funneling excitation energy from surrounding antenna units directly to the core PSII subunit CP47. The high concentration of fucoxanthin pigments within FCPII-2 enhances its ability to absorb diverse light wavelengths while simultaneously dissipating excess energy, thus safeguarding the photosynthetic apparatus from photodamage under intense light conditions. This dual functionality optimizes photosynthetic efficiency and cellular protection, a vital trait for survival in the fluctuating light environments of marine ecosystems.
Additionally, the study has characterized the previously enigmatic Psb36 protein subunit, localized at the interface between the PSII core and antenna system. Though Psb36 was known from earlier studies in diatoms and red algae, its amino acid sequence remained unidentified until this breakthrough. The discovery of Psb36’s sequence and its structural integration offers fresh insight into how photosynthetic complexes maintain stability and regulate energy transfer, highlighting intricate protein-protein interactions critical for photosystem functionality.
Marine algae, particularly haptophytes, are ecologically vital, contributing roughly half of the ocean’s biomass production and playing a central role in global carbon cycling. Yet, the molecular details underlying their photosynthetic machinery have been conspicuously underexplored relative to terrestrial plants and other algae groups. This study fills that gap by providing a molecular snapshot of how these algae’s light-harvesting antenna complexes are architecturally configured to meet the demands of their marine habitat, optimizing energy capture and electron transport efficiency.
The researchers emphasize that the unique antenna arrangement in C. roscoffensis‘ PSII supports highly efficient light harvesting tailored to the marine photic environment where fluctuating light intensities and spectral compositions pose challenges for photosynthetic organisms. The structural insights suggest potential mechanisms through which these algae maximize photon utilization while minimizing photoinhibition, a balance critical for their survival and productivity.
These revelations not only extend fundamental biological knowledge but also have profound implications for artificial photosynthesis. By mimicking the arrangement and pigment composition of the FCPII antenna complexes and their integration with PSII, synthetic systems could be engineered to achieve higher light-harvesting efficiencies and enhanced photoprotection. Such biomimetic designs could accelerate the development of solar fuel technologies, providing greener alternatives to fossil fuels and advancing energy sustainability goals globally.
The application of cryo-EM at near-atomic resolution marks a significant leap forward in structural biology, especially in studying challenging membrane protein complexes like photosystems. This technique offers unprecedented clarity in mapping pigment-protein interactions and electron transfer pathways, enabling researchers to dissect the subtleties of natural photosynthetic processes that have evolved over billions of years.
Dr. La Rocca remarked on the unexpected findings, noting that the distinctive antenna protein arrangement in C. roscoffensis contrasts with well-characterized systems in other photosynthetic organisms, underscoring nature’s versatility in optimizing energy capture. He highlighted that understanding these variations could provide critical design cues for tailored synthetic photosystems capable of operating under diverse environmental conditions.
Concluding the study, Professor Jian-Ren Shen emphasized the potential of these discoveries to propel artificial photosynthesis research. By unraveling the molecular intricacies of highly efficient natural photosystems, scientists are moving closer to emulating and surpassing nature’s solutions for solar energy conversion, a revolutionary step toward sustainable energy futures.
Okayama University, as the host institution for this research, continues its mission to advance interdisciplinary science for global sustainability. Their commitment is reflected in supporting pioneering studies like this, which blend structural biology, biophysics, and environmental science to tackle some of the most pressing challenges facing humanity today.
This landmark study was published in Nature Communications on May 5, 2025, underlining the remarkable progress being made at the interface of marine biology and renewable energy research. As the quest to harness sunlight with increased efficiency accelerates, these molecular insights pave the way for innovations that could transform how we generate and consume energy on a planetary scale.
Subject of Research: Cells
Article Title: Structure of a photosystem II-FCPII supercomplex from a haptophyte reveals a distinct antenna organization
News Publication Date: 5-May-2025
Web References: https://doi.org/10.1038/s41467-025-59512-9
Image Credits: Credit: Robin Mejia and Dr. Alison Taylor from Wikimedia Commons
Keywords: Life sciences, Plant sciences, Photosynthesis, Marine photosynthesis, Biomolecular structure, Molecular biology, Marine resources, Photosystems, Sustainable energy, Algae, Marine ecosystems
