1.
Ubiquitous Structural Signaling in Bacterial Phytochromes.
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Björling, A
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Berntsson, O
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Takala, H
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Gallagher, KD
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Patel, H
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Gustavsson, E
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St Peter, R
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Duong, P
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Nugent, A
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Zhang, F
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Berntsen, P
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Appio, R
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Rajkovic, I
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Lehtivuori, H
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Panman, MR
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Hoernke, M
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Niebling, S
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Harimoorthy, R
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Lamparter, T
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Stojković, EA
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Ihalainen, JA
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Westenhoff, S
Abstract:
The phytochrome family of light-switchable proteins has long been studied by biochemical, spectroscopic and crystallographic means, while a direct probe for global conformational signal propagation has been lacking. Using solution X-ray scattering, we find that the photosensory cores of several bacterial phytochromes undergo similar large-scale structural changes upon red-light excitation. The data establish that phytochromes with ordinary and inverted photocycles share a structural signaling mechanism and that a particular conserved histidine, previously proposed to be involved in signal propagation, in fact tunes photoresponse.
2.
Connection between absorption properties and conformational changes in Deinococcus radiodurans phytochrome.
Abstract:
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 subdomains. The photosensory unit (DrCBD-PHY) shows an unusually stable Pfr state with minimal dark reversion, whereas the histidine kinase (HK) domain facilitates dark reversion to the resting state. Size-exclusion chromatography reveals that all phytochrome fragments remain as dimers in the illuminated state and dark state. Still, the elution profiles of all phytochrome 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 PHY 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 oligomerization of DrBphP can be diminished by converting the molecule back to the resting Pr state by using far-red light.
