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Structure. 2012 Aug 8;20(8):1436-46. doi: 10.1016/j.str.2012.06.002. Epub 2012 Jul 12.

Structure of a bacteriophytochrome and light-stimulated protomer swapping with a gene repressor.

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1
Institute of Integrative Biology, Biosciences Building, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK.

Abstract

Phytochromes are photoreceptors in phototropic organisms that respond to light conditions by changing interactions between a response regulator and DNA. Bacterial phytochromes (BphPs) comprise an input photosensory core domain (PCD) and an output transducing domain (OTD). We report the structure of a BphP containing both PCD and the majority of its OTD, and demonstrate interaction with its cognate repressor. The OTD of RpBphP1, from Rhodopseudomonas palustris, is composed of a PAS/PAC domain and, to our knowledge, a hitherto unrecognized two-helix output sensor (HOS) domain. Unlike canonical BphPs, it does not transmit phosphorelay signals but forms a complex with the transcriptional repressor RpPpsR2 on photoconversion with far-red light. We show that HOS is essential for complex formation and that the anti-parallel dimer geometry is crucial in achieving HOS domain activation and protomer swapping under the control of light. These results provide insights into the steps taken by a two-component signaling system.

PMID:
22795083
DOI:
10.1016/j.str.2012.06.002
[Indexed for MEDLINE]
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