Tips and turns of bacteriophytochrome photoactivation

Abstract

Phytochromes are red light-sensing photoreceptors. Here we review the current understanding of phytochrome photoactivation, with a special focus on bacteriophytochromes and their crystallographic studies.

The structural changes in the signaling mechanism of bacteriophytochromes in solution revealed by a multiscale computational investigation

“…In particular, we have shown that the connection between the conformation of the chromophore and the following largescale changes in the secondary and tertiary structure of the PSM is not univocal thus allowing the phytochrome to exploit redundant routes for its activation. 17,18…”

“…We conclude this analysis by recalling that a single-point mutation of the conserved Tyr263 residue resulted in a decoupling between the chromophore state and the conformation of the PSM. 17,18 In fact, the Y263F mutant PSM could adopt a Pfrlike overall structure and a a-helix conformation for the tongue, with the chromophore in the Pr state. These experimental results suggest that the entire opening mechanism of the PSM is controlled by the tongue conformation, and not by the chromophore directly.…”

“…In the literature different models have been proposed for the Pr-to-Pfr photoreaction, possibly involving one or more intermediates. 6,[13][14][15][16][17][18][19] The rst guess about the photo-induced isomerization process in the Deinococcus radiodurans bacteriophytochrome (DrBph) was given when crystal structures were rstly published for both Pr and Pfr PSM isomers. 20 By a structural X-ray comparison, it was possible to see that the largest difference between the two states is represented by the tongue secondary structure and the straightening of the spine, with the latter directly implicating a larger distance between the PHY domains in the Pfr state (see Fig.…”

Structural basis for the Pr-Pfr long-range signaling mechanism of a full-length bacterial phytochrome at the atomic level

“…The prototypical BphP architecture consists of an N-terminal photosensory module (PSM), which autocatalytically binds biliverdin IXα (BV) chromophore to a conserved cysteine residue, and a C-terminal variable output module (OM), responsible for transducing the PSM light-driven conformational changes into a specific physiological signal ( 5 – 9 ).…”

“…BphPs usually show a dimeric quaternary structure, where monomers are docked to each other in a parallel or antiparallel arrangement through long helical bundles across the different domains called GAF-PHY and PHY-OM helical linkers, which form the “helical spine” ( 6 , 7 ). Other outstanding structural features from these photoreceptors are (i) the presence of a figure-of-eight knot that crosses over residues between the PAS and GAF domains, strengthening their association ( 10 ), and (ii) a highly conserved hairpin protrusion from the PHY domain, termed as the “tongue”, which encloses the chromophore binding pocket by interacting electrostatically with the GAF domain ( 6 – 9 ).…”