Structural basis for gene regulation by a [B.sub.12]-dependent photoreceptor

Photoreceptor proteins enable organisms to sense and respond to light. The newly discovered CarH-type photoreceptors use a vitamin [B.sub.12] derivative, adenosylcobalamin, as the light-sensing chromophore to mediate light-dependent gene regulation. Here we present crystal structures of Thermus ther...

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Bibliographic Details
Published in:Nature (London) 2015-10, p.536
Main Authors: Jost, Marco, Fernandez-Zapata, Jesus, Polanco, Maria Carmen, Ortiz-Guerrerost, Juan Manuel, Chen, Percival Yang- Ting, Kang, Gyunghoon, Padmanabhan, S, Elias-Arnanz, Montserrat, Drennan, Catherine L
Format: Article
Language:English
Subjects:
Bacteria, Thermophilic
Genetic aspects
Genetic regulation
Observations
Photoreceptors
Physiological aspects
Proteins
Structure
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Summary:Photoreceptor proteins enable organisms to sense and respond to light. The newly discovered CarH-type photoreceptors use a vitamin [B.sub.12] derivative, adenosylcobalamin, as the light-sensing chromophore to mediate light-dependent gene regulation. Here we present crystal structures of Thermus thermophilus CarH in all three relevant states: in the dark, both free and bound to operator DNA, and after light exposure. These structures provide visualizations of how adenosylcobalamin mediates CarH tetramer formation in the dark, how this tetramer binds to the promoter -35 element to repress transcription, and how light exposure leads to a large-scale conformational change that activates transcription. In addition to the remarkable functional repurposing of adenosylcobalamin from an enzyme cofactor to a light sensor, we find that nature also repurposed two independent protein modules in assembling CarH. These results expand the biological role of vitamin [B.sub.12] and provide fundamental insight into a new mode of light-dependent gene regulation.
ISSN:0028-0836
1476-4687
DOI:10.1038/naturel4950