Summary: Researchers have identified a new photoreceptor that is roughly 50 times more efficient at capturing light than the rhodopsin found in the human eye.
Source: University of Michigan
New Photoreceptor LITE-1 Is Exceptionally Efficient at Capturing UV Light
An international research team led by the University of Michigan reports the discovery of LITE-1, a novel type of photoreceptor found in invertebrates. LITE-1 is only the third distinct class of animal photoreceptor identified to date and absorbs ultraviolet light far more efficiently than known animal photoreceptors. The results were published online November 17 in the journal Cell.
The LITE-1 protein was identified among a family of taste receptor homologs in the roundworm Caenorhabditis elegans, a widely used model organism in biological research. Unlike the opsins and cryptochromes previously characterized in animals, LITE-1 exhibits a remarkably high photon-capturing capacity—approximately 10 to 100 times greater than those other photoreceptors, and roughly 50 times more efficient than human rhodopsin in certain metrics.
Although C. elegans lack conventional eyes, prior observations showed the worms move away from bright light. The new experiments demonstrate that LITE-1 itself directly absorbs UV-A and UV-B light and initiates the worm’s light-avoidance response, rather than acting indirectly by detecting light-generated chemical signals.
According to senior author X.Z. Shawn Xu of the U-M Life Sciences Institute, LITE-1’s efficiency and unusual properties raise several possible applications and open new directions for research. For example, with further development LITE-1 or derivatives might be used as a UV-absorbing additive in protective formulations or as a tool to confer light sensitivity to otherwise insensitive cells for laboratory studies.
Distinct Mechanism and Structural Requirements
Unlike classical animal photoreceptors that rely on a separate chromophore molecule (such as retinal, derived from vitamin A) to capture photons, LITE-1 depends strictly on its protein conformation to absorb light. When the protein is denatured, it loses its light-absorbing ability entirely rather than retaining partial function as isolated chromophores sometimes do. This finding indicates that LITE-1 represents a fundamentally different photoreception mechanism.
Biochemical and genetic analyses revealed that two specific tryptophan amino acids within LITE-1 are critical for its photosensitive function. Introducing equivalent tryptophan residues into a closely related, normally non-light-sensitive family member (GUR-3) produced a protein that gained substantial sensitivity to ultraviolet light—achieving roughly one-third of LITE-1’s UV-B responsiveness. These results suggest targeted engineering could create new photoreceptors by altering key residues in related proteins.
Significance and Future Directions
LITE-1 expands the known repertoire of animal photoreceptors and suggests that previously unrecognized types of light-sensitive proteins may exist across species. Its high extinction coefficient for UVA and UVB wavelengths makes it a powerful model for studying efficient photon capture at the protein level. Future work will aim to resolve the structural basis for LITE-1’s exceptional absorption, determine how it transduces light into cellular signals, and explore practical applications such as molecular tools for optogenetics or UV-protective materials.
The study was led by researchers at the University of Michigan with collaborators from Huazhong University of Science and Technology, Case Western Reserve University, and St. Jude Children’s Research Hospital. Lead and contributing authors include Jianke Gong, Yiyuan Yuan, Alex Ward, Lijun Kang, Bi Zhang, Zhiping Wu, Junmin Peng, Zhaoyang Feng, Jianfeng Liu, and X.Z. Shawn Xu.
Funding: The work was supported by the National Eye Institute, the National Natural Science Foundation of China, the Chinese Ministry of Education, the Program for Changjiang Scholars and Innovative Research Team in University, and the National Institute of General Medical Sciences.
Abstract (Condensed)
LITE-1, a seven-transmembrane gustatory receptor homolog in C. elegans, functions as a bona fide photoreceptor for UVA and UVB light. It displays an unusually high efficiency of photon capture, with an extinction coefficient 10–100 times higher than opsins and cryptochromes. Photoabsorption by LITE-1 strictly depends on the native protein conformation and requires two tryptophan residues identified as essential for function. Altering a related receptor to include analogous tryptophans enhances its photosensitivity, indicating a potential route to engineer novel photoreceptors. LITE-1 thus represents a distinct and previously unrecognized class of animal photoreceptor.
This summary is based on the peer-reviewed article “The C. elegans Taste Receptor Homolog LITE-1 Is a Photoreceptor,” published in Cell (November 17, 2016) by Jianke Gong et al., with X.Z. Shawn Xu as senior author.