Connection between Absorption Properties and Conformational Changes in Deinococcus radiodurans Phytochrome

Phytochromes consist of several protein domains and a linear tetrapyrrole molecule, which interact as a red-light-sensing system. In this study, size-exclusion chromatography and light-scattering techniques are combined With UV-vis spectroscopy to investigate light-induced changes in dimeric Deinococcus radiodurans bacterial phytochrome (DrBphP and, its,subdornams. The potosensory unit (DrCBD-PHY), shows an unusually stable Pfr state with reversion, whereas the histidine, kinase (HK) domain facilitates dark reversion to the resting state. Size-exclusion chromatography reveals that all phytochrorne fragments remain as dimers in the illuminated state and dark state. Still, the elution profiles of all phytochronle fragments differ between the illuminated and dark states. The differences are observed reliably only when the whole UV-vis spectrum is characterized along the elution profile and show more Pfr-state characteristics at later elution volumes in DrBphP and DrCBD-PHY fragments. This implies that the Pliy:domain has an important role in amplifying and relaying light-induced conformational changes to the HK domain. In the illuminated state, the HK domain appears partially unfolded and prone to form oligomers. The oligoinerization of DrBphp can be diminished by converting the molecule back to the resting Pr state by using far-red light.