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 that of other cryptochromes and (6-4) photolyases. This blue light reaction of the oxidized flavin is not accompanied by any detectable changes in secondary structure, in agreement with a role in vivo of an unphysiological preactivation. In contrast, the conversion by red light of the neutral radical to the anionic fully reduced state proceeds with conformational changes in turn elements, which most probably constitute a part of the signaling process. These changes have not been detected in the corresponding transition of (6-4) photolyase, which points to a decisive difference between the sensor and the enzyme.
Physical and Biophysical Chemistry, Department of Chemistry, Bielefeld University , Universitätsstraße 25, 33615 Bielefeld, Germany.
Meike
M
Spexard
Christian
C
Thöing
Benedikt
B
Beel
Maria
M
Mittag
Tilman
T
Kottke
D016825:Chlamydomonas reinhardtii / Q000378:metabolism; D003116:Color; D056931:Cryptochromes / Q000737:chemistry*; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000737:chemistry*; D017666:Deuterium Oxide; D005420:Flavoproteins / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008027:Light; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared
D056931:Cryptochromes; D005420:Flavoproteins; D004255:Deoxyribodipyrimidine Photo-Lyase; D017666:Deuterium Oxide