Details

Autor(en) / Beteiligte

• Burgie, E. Sethe
• Walker, Joseph M.
• Phillips, George N.
• Vierstra, Richard D.

Titel

A Photo-Labile Thioether Linkage to Phycoviolobilin Provides the Foundation for the Blue/Green Photocycles in DXCF-Cyanobacteriochromes

Ist Teil von

• Acta crystallographica. Section E, Structure reports online, 2013-01, Vol.21 (1), p.88-97

Ort / Verlag

United States: Elsevier Ltd

Erscheinungsjahr

2013

Quelle

Access via ScienceDirect (Elsevier)

Beschreibungen/Notizen

• The phytochrome superfamily encompasses a diverse collection of photochromic photoreceptors in plants and microorganisms that employ a covalently linked bilin cradled in a cGMP-phosphodiesterase/adenylyl-cyclase/FhlA (GAF) domain to detect light. Whereas most interconvert between red- and far-red-light-absorbing states, cyanobacteria also express variants called cyanobacteriochromes (CBCRs) that modify bilin absorption to collectively perceive the entire visible spectrum. Here, we present two X-ray crystallographic structures of the GAF domain from the blue/green photochromic CBCR PixJ from Thermosynechococcus elongatus. These structures confirm the hypothesis that CBCRs variably manipulate the chromophore π-conjugation system through isomerization and a second thioether linkage, in this case involving the bilin C10 carbon and Cys494 within a DXCF sequence characteristic of blue/green CBCRs. Biochemical studies support a mechanism for photoconversion whereby the second linkage ruptures on route to the green-light-absorbing state. Collectively, the TePixJ(GAF) models illustrate the remarkable structural and photochemical versatility among phytochromes and CBCRs in driving light perception. ▸ The Te-PixJ structure reveals the positions of the two DXCF-CBCR thioether linkages ▸ For blue/green photocycling, Te-PixJ utilizes a phycoviolobilin chromophore ▸ Rupture of the noncanonical DXCF thioether coincides with Pb/Pg photoconversion ▸ Te-PixJ bilin-binding and photochemistry diverge greatly from canonical phytochromes Phytochromes use a thioether-linked bilin to interconvert between red- and far-red light-absorbing states. Burgie et al. describe structures of PixJ, a cyanobacteriochrome, and how it enforces a blue/green photocycles by manipulating bilin π-conjugation through isomerization and a photo-labile thioether-linkage.