Discovery of a New Transport Protein that Binds to Cyclic Sugars: Elucidating Unique Substrate Recognition Suitable for Cyclic β-1,2-Glucan

【Research Summary and Highlights】Cyclic sugars are expected to have medical applications due to their ability to encapsulate other molecules. We have discovered a new sugar transport protein that binds to both cyclic and linear β-1,2-glucan and can import them into cells. Structural analysis suggests that in this transport protein, the curved substrate binds at its central portion, making it suitable for cyclic sugar binding. This result serves as a foundation for research into the application of cyclic sugars in the pharmaceutical and food sectors. 【Research Overview】A research team led by Associate Professor Masahiro Nakajima of the Tokyo University of Science, Professor Hidetaka Torigoe of the same university, and Associate Professor Hiroyuki Nakai of Niigata University has discovered the world's first sugar transport protein capable of importing β-1,2-glucan, a sugar chain where glucose is linked in a special manner, into cells. β-1,2-glucan is involved in various life phenomena such as bacterial pathogenicity and symbiosis. Cyclic β-1,2-glucan, in particular, is expected to be used as an inclusion compound. While Associate Professor Nakajima and his colleagues have previously focused on this sugar chain and accumulated knowledge on degrading enzymes, the transport mechanism for importing β-1,2-glucan into cells remained largely unknown. The research group identified a candidate protein (Chy400_4166) by searching the genome of Chloroflexus aurantiacus, a type of filamentous photosynthetic bacterium important for understanding the evolution of photosynthesis, and performed functional analysis and X-ray crystallography. The results revealed that Chy400_4166 binds to cyclic and linear β-1,2-glucan with high affinity and possesses a novel binding mechanism fundamentally different from known β-1,2-glucooligosaccharide transport proteins. This discovery not only contributes to understanding the transport system of β-1,2-glucan and the mechanisms of bacterial pathogenicity and symbiosis but also provides fundamental knowledge for understanding the behavior of cyclic sugars in vivo, which is expected to form the basis for future medical applications. This research result was published online in the international academic journal 'FEBS Journal' on May 10, 2026.