Milliseconds to seconds timescale, filling the gap in the photo-reaction of carH with time-resolved X-ray scattering in solution.

The protein carH associates with the B12 vitamin to form a light-sensitive gene repressor in bacteria. The gene repressive state in the dark binds to the DNA as a tetramer. The light triggers the dissociation of the adenosyl group from the cobalamin, the coordination of the cobalt to the H132 of carH and the dissociation of the tetramer. We recently obtained time-resolved wide-angle X-ray scattering (TR-WAXS) results regarding the tetramer to monomer transition of a truncated form of carH (TtCBD) but we still lack information about the oligomerization change for the full-length carH and for two other variants, the TtH132A mutant and the HmCBD homologue. To this end, TR-WAXS will be used on ID09. Preliminary results on TtCBD show the presence of two structural intermediates relaxing within 3 ms and 300 ms before the tetramer dissociation occurs. We aim at collecting data on the other carH variants for long time delays ranging from 100 ms to 5 s as recently achieved on ID09 for TtCBD.