How Crystals Grown in “Kibo” Revealed the Bioluminescence Mechanism of Sea Fireflies

Through the High-Quality Protein Crystal Growth Experiment conducted using the Japanese Experiment Module “Kibo” aboard the International Space Station, researchers successfully determined the three-dimensional structure of the enzyme luciferase (CLuc), which is responsible for the light emission of sea fireflies.
This achievement was the result of a joint research project between the National Institute of Advanced Industrial Science and Technology (Principal Investigator: Yasuo Mitani, Director of the Molecular Biosystems Research Institute) and the Japan Aerospace Exploration Agency(JAXA).

Sea fireflies are marine organisms known for emitting beautiful blue light. However, the way in which their luminescent reaction proceeds inside the enzyme CLuc had long remained a major mystery.
In this study, high-quality protein crystals—difficult to obtain on Earth—were grown under the microgravity environment of “Kibo,” and detailed structural analyses were carried out. As a result, researchers clarified the spatial structure by which CLuc incorporates the luminescent substrate, as well as the arrangement of amino acid residues thought to be important for the reaction.

These findings are expected not only to deepen our understanding of the sophisticated mechanisms by which living organisms produce light but also to contribute to applications such as highly sensitive biosensors, medical diagnostic technologies, and next-generation imaging technologies. JAXA will continue promoting research that contributes to society through space experiments utilizing “Kibo.”