Life on Earth follows a curious rule: most of its essential molecules come in just one “handedness.” DNA twists to the right, and the proteins that keep our cells running are built from left-handed amino acids. Scientists have long believed this molecular one-sidedness helped early life remain stable and efficient.
But a new study has revealed a surprising exception: a rare ambidextrous protein that functions in both mirror-image forms. This discovery could offer clues to a time when life may have existed with opposite molecular orientations — a concept sometimes called “mirror life.”
Liam Longo, a researcher at the Tokyo Earth-Life Science Institute, was studying a short protein segment called a helix-hairpin-helix motif, which is commonly found in proteins that repair DNA. He noticed that the structure was symmetrical — and wondered if that symmetry allowed it to work in both left- and right-handed forms.
To find out, his team created mirror-image versions of the protein, including an ancient version believed to resemble one from the last universal common ancestor (LUCA). They discovered that both forms could bind DNA — even mirror-image DNA — just as effectively. This suggests that the protein’s structure is inherently flexible, able to interact with DNA regardless of its orientation.
One explanation is that this flexibility evolved to help the protein recognize many forms of DNA. But Longo also raises a wilder idea: perhaps this protein dates back to a time when mirror-image life actually existed.
Whether or not such life ever evolved, the finding is exciting. As scientists move toward creating synthetic or artificial life, ambidextrous proteins like this one could become key tools — bridging natural biology and its mirror image in a whole new chapter of evolution.
Serra Húnter Fellow of Sociology at Universitat Rovira i Virgili.
Former DAAD-Gastprofessorin at Julius-Maximilians-Universität Würzburg