Phytochromes sense red light in plants and various microorganism. Light absorption causes
structural changes within the protein, which alter its biochemical activity. Bacterial
phytochromes are dimeric proteins, but the functional relevance of this arrangement remains
unclear. Here, we use time-resolved X-ray scattering to reveal the solution structural change
of a monomeric variant of the photosensory core module of the phytochrome from
Deinococcus radiodurans. The data reveal two motions, a bend and a twist of the PHY …