Biology subjects

Isaksson, L.

Publications and source records attributed to Isaksson, L..

2 recordsLinked to original sources

bioRxiv2020

Signaling mechanism of phytochromes in solution

Phytochrome proteins guide the red/far-red photoresponse of plants, fungi, and bacteria. The proteins change their structure in response to light, thereby altering their biochemical activity. Crystal structures suggest that the mechanism of signal transduction from the chromophore to the output domains involves refolding of the so-called PHY tongue. It is currently not clear how the two other notable structural features of the phytochrome superfamily, the helical spine and a figure-of-eight knot, are involved in photoconversion. Here, we present solution NMR data of the complete photosensory core module from D. radiodurans (Dr BphP). Photoswitching between the resting and active states induces changes in amide chemical shifts, residual dipolar couplings, and relaxation dynamics. All observables indicate a photoinduced structural change in the knot region and lower part of the helical spine. This implies that a conformational signal is transduced from the chromophore to the helical spine through the PAS and GAF domains. The new pathway underpins functional studies of plant phytochromes and may explain photo-sensing by phytochromes under biological conditions.

biochemistry↗

bioRxiv2019

The primary structural photoresponse of phytochrome proteins captured by a femtosecond X-ray laser

Phytochrome proteins control the growth, reproduction, and photosynthesis of plants, fungi, and bacteria. Light is detected by a bilin cofactor, but it remains elusive how this leads to activation of the protein through structural changes. We present serial femtosecond X-ray crystallographic data of the chromophore-binding domains of a bacterial phytochrome at delay times of 1 ps and 10 ps after photoexcitation. The structures reveal a twist of the D-ring, which lead to partial detachment of the chromophore from the protein. Unexpectedly, the conserved so-called pyrrole water is photodissociated from the chromophore, concomitant with movement of the A-ring and a key signalling aspartate. The changes are wired together by ultrafast backbone and water movements around the chromophore, channeling them into signal transduction towards the output domains. We suggest that the water dissociation is key to the phytochrome photoresponse, explaining the earliest steps of how plants, fungi and bacteria sense red light.

biophysics↗