Structural changes in a model photoreceptor protein: use of rational variants to disentangle different classes of motions

Photoreceptors regulate the adaptation of living organisms to light. A class of photoreceptors recently discovered uses a vitamin B12 derivative to sense light and regulate the biosynthesis of carotenoids, which protect against photo-oxidative damage. The CarH photoreceptor is a prototype of this class and as it acts as a light-activated transcription regulator it is a promising target for optogenetic applications. We have recently shown that tertiary and quaternary structural changes can be followed in T. thermophilus (Tt) CarH after light absorption by time-resolved small and wide angle X-ray scattering (Exp. LS-2958). We propose to extend the results of LS-2958 to both a variant and a homolog of TtCarH, where major quaternary changes are prevented. The new results will be essential to disentangle tertiary and quaternary signals in TtCarH thus enabling us to describe the cascade of structural events occurring in native TtCarH in the micro- to millisecond time scale.