Response of the Sensory Animal-like Cryptochrome aCRY to Blue and Red Light As Revealed by Infrared Difference Spectroscopy

Cryptochromes act as blue light sensors in plants, insects, fungi, and bacteria. Recently, an animal-like cryptochrome (aCRY) was identified in the green alga Chlamydomonas reinhardtii by which gene expression is altered in response to not only blue light but also yellow and red light. This unique response of a flavoprotein in vivo has been attributed to the fact that the neutral radical of the flavin chromophore acts as dark form of the sensor, which absorbs in almost the entire visible spectral range (<680 nm). Here, we investigated light-induced processes in the protein moiety of full-length aCRY by UV–vis and Fourier transform infrared spectroscopy. Findings are compared to published results on the homologous (6-4) photolyases, DNA repair enzymes. The oxidized state of aCRY is converted to the neutral radical by blue light. The recovery is strongly dependent on pH and might be catalyzed by a conserved histidine of the (6-4)/clock cluster. The decay is independent of oxygen concentration in contrast to...