Structural changes in a model photoreceptor protein: quaternary transitions in the milliseconds to seconds time scale

The CarH photoreceptor is a light-activated transcription regulator and it is a promising target for optogenetic applications. We have recently shown that structural changes in CarH after light absorption can be followed by time-resolved X-ray scattering (LS-2958). To disentangle tertiary and quaternary signals, we performed a second experiment ( LS-3091) on a mutant (H132A-CarH) and a homolog of CarH in which quaternary changes are prevented or modified, respectively. The previous experiments enabled us to follow the cascade of structural events occurring in CarH on a time scale from µs to hundreds of ms. A comparison with static data showed that the relevant time scale of the photoreaction in native CarH extends longer than hundreds of ms, most likely because of the presence of large scale slow quaternary changes leading to the photoproduct. Here we propose to complete our study by collecting time-resolved scattering data in native CarH on the time scale from ms to several s.