(Press-News.org)
Corals may lack eyes, but they are far from blind. These delicate animals sense light in ways that continue to amaze and inspire the scientific community.
Researchers from Osaka Metropolitan University’s Graduate School of Science have uncovered a unique light-sensing mechanism of reef-building corals, in which light-detecting proteins, known as opsins, use chloride ions to flip between UV and visible light sensitivity depending on the pH of their surroundings. Their findings suggest a unique functionality that expands our understanding of vision and photoreception across the animal kingdom.
Animal vision relies on opsins, which are proteins that detect light using a small molecule called retinal. Retinal, however, naturally absorbs ultraviolet (UV) light only, meaning it sees shorter light than the visible light that we see. To extend its sensitivity into the visible range, retinal binds to the opsin to form a light-sensitive pigment through a special chemical bond called a Schiff base. This bond carries a positive charge that normally requires a nearby negatively charged amino acid, or counterion, to remain stable.
Anthozoans, such as corals and sea anemones, have opsins belonging to the anthozoan-specific opsins (ASO)-II group, which is a newly discovered opsin group. ASO-II opsins have properties that are different from the opsins of mammals.
“Some ASO-II opsins of reef-building corals lack the usual counterion amino acids found in other animal opsins,” said Akihisa Terakita, a professor at Osaka Metropolitan University’s Graduate School of Science and one of the lead authors of the study.
So, how do these opsins manage to ‘see’ visible light at all without these amino acids?
To understand this question, the team studied ASO-II opsins of the reef-building coral Acropora tenuis.
Using mutational experiments, spectroscopy, and targeted advanced simulation, the researchers found that instead of using amino acids, ASO-II opsins employ chloride ions (Cl⁻) from the surrounding environment as counterions. This is the first time scientists have reported an opsin that uses inorganic ions in this way.
“We found that chloride ions stabilize the Schiff base more weakly than amino acids do,” Yusuke Sakai, a postdoctoral researcher in Terakita's lab and the first author of the study, said, “so the opsin can reversibly switch between visible-light sensitivity and UV sensitivity depending on the pH.”
This suggests a mechanism where the opsin’s sensitivity depends on whether the retinal–opsin bond, Schiff base, is protonated or not, with pH shifting that balance. Low pH conditions increase number of protons, meaning the Schiff base becomes positively charged and absorbs longer wavelengths, including visible light. This is then stabilized by chloride. On the other hand, in high pH conditions, there are fewer protons, making the Schiff base deprotonated and absorbing UV light.
This pH-dependent switching may have ecological importance. Corals live in close symbiosis with algae that produce nutrients through photosynthesis. Since photosynthesis alters the pH inside coral cells, this may then shift opsin sensitivity between visible and UV light. This suggests that coral light sensitivity can adjust according to the algae’s photosynthetic activity — a new insight into their symbiotic relationship.
Beyond a better understanding of coral biology, the discovery could inspire new biotechnology. “The ASO-II opsin of Acropora tenuis was shown to regulate calcium ions in a light-dependent way, hinting at potential applications as an optogenetic tool whose wavelength sensitivity changes with pH,” Mitsumasa Koyanagi, a professor at Osaka Metropolitan University’s Graduate School of Science and one of lead authors of the study, said.
The study was published in eLife.
###
About OMU
Established in Osaka as one of the largest public universities in Japan, Osaka Metropolitan University is committed to shaping the future of society through the “Convergence of Knowledge” and the promotion of world-class research. For more research news, visit https://www.omu.ac.jp/en/ and follow us on social media: X, Facebook, Instagram, LinkedIn.
END
Breast milk is the first ‘super food’ for many babies. Full of vitamins, minerals, and other bioactive compounds, it helps build the young immune system and is widely considered the optimal source of infant nutrition. Not all mothers, however, have the opportunity to directly breastfeed multiple times during the day and night, and might use expressed milk stored for later.
Breast milk delivers a variety of cues from the mother to the infant, including signals that are thought to influence babies’ circadian rhythms. The hormones and proteins involved in circadian signaling, however, may vary in breast milk concentration ...
Researchers Shinjiro Takano, Yuya Hamasaki, and Tatsuya Tsukuda of the University of Tokyo have successfully visualized the geometric structure of growing gold nanoclusters in their earliest stages. During this process, they also successfully “grew” a novel structure of elongated nanoclusters, which they named “gold quantum needles.” Thanks to their responsiveness to light in the near-infrared range, these “needles” could enable much higher-resolution biomedical imaging and more efficient light-energy conversion. The findings were published in the Journal of the American ...
Niigata, Japan – A team of scientists have unveiled a breakthrough in the field of renewable energy materials. They have developed a transparent, crystalline mesoporous tungsten trioxide (WO₃) film that exhibited exceptional efficiency and stability for photoelectrochemical (PEC) water splitting. The innovation can accelerate the transition toward sustainable solar-to-hydrogen technologies, a clean energy pathway with far-reaching implications for global decarbonization. The research developed a transparent film of tungsten trioxide (WO₃) ...
Astronomers have gained insights into star formation by capturing the first spatially resolved detection of protostellar outflows and jets in the Milky Way’s outer region. The discovery, made using the Atacama Large Millimeter/submillimeter Array (ALMA), revealed that although the fundamental physics of star formation remains the same across different galactic environments, different chemistry or dust composition is observed in the outer Galaxy source.
The research focused on the protostellar source Sh 2-283-1a SMM1, located about 7.9 kiloparsecs (26,000 light-years) from the Sun ...
A new species of a native bushland marsupial – closely related to the kangaroo – has been discovered but is already likely extinct, new research shows.
Analysing fossils collected from caves of the Nullarbor and southwest Australia, researchers from Curtin University, the Western Australian Museum and Murdoch University uncovered a completely new species of bettong as well as two new subspecies of woylie.
Woylies are ecosystem engineers capable of turning over several tonnes of earth each year in search for their favourite mushroom treats. The cute kangaroo relatives, native to Western Australia, are the country’s ...
Former male high-level rugby players in New Zealand have a 22 percent increased risk of developing Alzheimer’s and other dementias later in life compared to men in the general population, according to new research from the University of Auckland.
The project is co-led by senior lecturer Dr Stephanie D’Souza from the COMPASS Research Centre in the University’s Faculty of Arts and Education and Dr Ken Quarrie from New Zealand Rugby.
Researchers examined long-term neurodegenerative disease risk outcomes for almost 13,000 men who played provincial-level or higher rugby between 1950 and 2000 and compared them with 2.4 million New Zealand men, matched on age, ...
In the criminal justice system, decisions about when and how long to detain people have historically been made by other people, like judges and parole boards. But that process is changing: Decision-makers increasingly include artificial intelligence systems in a variety of tasks, from predicting crime to analyzing DNA to recommending prison sentences. The use of AI in these domains raises pressing questions about how these computing systems use data to make predictions and recommendations, as well as larger questions about how to safeguard fairness in an AI age.
Notably, many AI systems are “black ...
Less than half of England has access to tirzepatide (Mounjaro) through their GP, despite the NHS roll-out of the weight-loss jab officially starting over two months ago, an investigation by The BMJ has found.
Due to the large number of people who could benefit from tirzepatide - an estimated 3.4 million people - and the drug’s price, NHS England and its spending watchdog, the National Institute for Health and Care Excellence, agreed the injections would be rolled out in phases over a 12-year period, which commenced on 23 June 2025, explains Elisabeth Mahase. Yet just 18 out of 42 commissioning bodies (43%) across the country ...
Researchers observed mother–infant interactions in urban UK and rural Ugandan communities, focussing on how mothers soothed their babies following naturally occurring episodes of distress.
They found that although the UK mothers responded to their babies' distress more quickly, Ugandan infants actually recovered faster.
This challenges long-standing assumptions rooted in Western models of parenting by showing that maternal promptness is not the only factor influencing how infants manage ...
From images of fruit to claims of being ‘sugar-free’, baby foods often feature misleading claims aimed at convincing parents the products are a healthy choice, new research shows.
The study led by the University of Auckland, reviewed packaging of more than 200 processed foods for infants and toddlers and found all featured marketing and nutrition claims, which didn’t necessarily stack up when they examined the ingredients. See Nutrition and Dietetics.
“These little packages are cluttered ...
