Photoinduced reaction mechanisms in prototypical and bathy phytochromes

Abstract

Phytochromes, found in plants, fungi, and bacteria, exploit light as a source of information to control physiological processes via photoswitching between two states of different physiological activity, i.e. a red-absorbing...

Light cues induce protective anticipation of environmental water loss in terrestrial bacteria

“…Phytochromes are typically considered to be red/far-red light sensors that interconvert between a red light-absorbing Pr state and a far-red light-absorbing Pfr state ( 26 ). However, our transcriptome data demonstrating parallel BphP1-mediated responses to red, far-red, and blue light, along with our prior demonstration of BphP1-mediated regulation of swarming motility under blue light ( 9 ), indicated that B728a BphP1, like certain other phytochromes ( 14 , 20 , 27 – 29 ), may be an exception to the canonical phytochrome model.…”

Vibrational Spectroscopy of Phytochromes

“…Campestris , in which the Pfr state prevails at ambient temperature [ 112 ]. Here, only the sequential H/D exchange is observed in the Pfr state, whereas the chromophore exhibits a heterogeneous structure, and its propionic side chain is deprotonated [ 110 ].…”

“…However, the ground state heterogeneity of Pr (also in the case of Cph1Δ2) is due to more subtle structural differences that do not affect electronic transitions to a detectable extent. Such differences include, as is the case in Pfr, the C-D and, specifically, the A-B methine bridge, as reflected by the pairwise appearance of the same mode (e.g., A-B stretching, Figure 2 ) [ 106 , 110 , 115 ]. In addition, a recent 2D IR study on Dr BphP ( Deinococcus radiodurans ) revealed heterogeneity in the hydrogen bonding environment of the ring C=O group [ 116 ].…”

“…The sequence of the cryo-trapped intermediates following Lumi-R are Meta-Ra, Meta-Rc, and Pfr for the Pr → Pfr photo-conversion of both prototypical and bathy phytochromes. The RR spectroscopic characterization of Meta-Ra in all phytochromes studied so far revealed a protonated chromophore and low HOOP activities corresponding to sterically relaxed methine bridges [ 51 , 110 , 122 , 137 ]. The frequency of the C-D stretching mode is upshifted compared to the Lumi-R states and is, again, close to or even higher than that of Pr.…”

“…Chromophore deprotonation has originally been proposed on the basis of RR spectra excited in resonance with the second electronic transition [ 56 , 57 ]. This conclusion was initially questioned by the Hildebrandt group [ 51 ] but later confirmed for plant as well as bacterial phytochromes [ 52 , 70 , 110 , 118 , 119 , 137 ]. The release of the proton from the chromophore is linked to the transfer of a proton to the solution phase, as shown for Agp1 and Cph1Δ2 [ 52 , 117 , 118 ].…”