UC Davis

Cyanobacteriochrome RcaE regulates Type III complementary chromatic adaption in the cyanobacterium Fremyella diplosiphon by photoswitching between a green-absorbing dark state (15ZPg) and red-absorbing photoproduct (15EPr). Ultrafast photodynamics of RcaE involve tautomerization of the bilin chromophore, inhomogeneity, and the generation of three primary photointermediates in the forward reaction (Lumi-Go, Lumi-Gr, and Lumi-Gf). The secondary photodynamics reported here show that only Lumi-Go evolves to 15EPr via spectrally similar Meta-Go1 and Meta-Go2 intermediates, with a protonation reaction occurring at the final step on the millisecond timescale. Reverse reaction dynamics were characterized and reveal an unusually long-lived Lumi-Rf photoproduct and a blue-shifted Meta-Ry intermediate.