B12 plays an important role in Photoreceptor Proteins

A group of scientists has discovered and mapped a light-sensing protein that uses vitamin B12 to perform key functions including gene regulation.
The result comes from studying proteins from the bacterium Thermus thermophilus. It involves at least two findings of broad interest.
Firstly, 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.
Secondly, the result shows a new mode of gene regulation, in which the light-sensing proteins play a key role. The bacteria have repurposed existing protein structures that use vitamin B12, and put them to work in new ways, according to the scientists' observation.
The paper describes the photoreceptors in three different states - in the dark, bound to DNA, and after being exposed to light. The finding helps the scientists get all the series of structures and understand how it works at each stage. The details can be found in the journal Nature.
There are nine co-authors of this paper including professor Catherine Drennan of chemistry and biology at MIT, graduate students Percival Yang-Ting Chen, Marco Jost, and Gyunghoon Kang of MIT; Jesus Fernandez-Zapata and S. Padmanabhan of the Institute of Physical Chemistry Rocasolano, in Madrid; and Monserrat Elias-Arnanz, Juan Manuel Ortiz-Guerreo, and Maria Carmen Polanco, of the University of Murcia, in Murcia, Spain.
By studying the structures of the photoreceptor proteins in their three states, the scientists developed a more thorough understanding of the structures, and their functions, than they would have by viewing the proteins in just one state.
Microbes benefit from knowing whether they are in light or darkness. The photoreceptors bind to the DNA in the dark, and prevent activity pertaining to the genes of Thermus thermophilus. When light hits the microbes, the photoreceptor structures cleave and "fall apart," as Drennan puts it, and the bacteria start producing carotenoids, which protect the organisms from negative effects of sunlight, such as DNA damage.
The research also suggests that the exact manner in which the photoreceptors bind to the DNA is novel. The structures contain tetramers, four subunits of the protein, of which three are bound to the genetic material.
The finding is believed to have practical application in the future including the engineering of light-directed control of DNA transcription, or the development of controlled interactions between proteins.
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