A natural light switch
MIT scientists, working with colleagues in Spain, have discovered and mapped a light-sensing protein that uses vitamin B12 to perform key functions, including gene regulation. The result, derived from studying proteins from the bacterium Thermus thermophilus, involves at least two findings of broad interest. First, it expands our knowledge of the biological role of vitamin B12, which was already understood to help convert fat into energy, and to be involved in brain formation, but has now been identified as a key part of photoreceptor proteins — the structures that allow organisms to sense and respond to light. Second, the research describes a new mode of gene regulation, in which the light-sensing proteins play a key role. In so doing, the scientists observe, the bacteria have repurposed existing protein structures that use vitamin B12, and put them to work in new ways. “Nature borrowed not just the vitamin, but really the whole enzyme unit,...