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

Spexard M, Thöing C, Beel B, Mittag M, Kottke T. Response of the Sensory Animal-like Cryptochrome aCRY to Blue and Red Light As Revealed by Infrared Difference Spectroscopy. Biochemistry. 2014;53(6):1041-1050

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 <i>Chlamydomonas reinhardtii</i> 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 <i>in vivo</i> 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 <i>in vivo</i> 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

A Flavin-Binding Cryptochrome Photoreceptor Responds to Both Blue and Red Light in Chlamydomonas reinhardtii

Beel B, Prager K, Spexard M, et al. A Flavin-Binding Cryptochrome Photoreceptor Responds to Both Blue and Red Light in Chlamydomonas reinhardtii. THE PLANT CELL. 2012;24(7):2992-3008.Cryptochromes are flavoproteins that act as sensory blue light receptors in insects, plants, fungi, and bacteria. We have investigated a cryptochrome from the green alga Chlamydomonas reinhardtii with sequence homology to animal cryptochromes and (6-4) photolyases. In response to blue- and red light exposure, this animal-like cryptochrome (aCRY) alters the light-dependent expression of various genes encoding proteins involved in chlorophyll and carotenoid biosynthesis, light-harvesting complexes, nitrogen metabolism, cell cycle control, and the circadian clock. Additionally, exposure to yellow but not far-red light leads to comparable increases in the expression of specific genes; this expression is significantly reduced in an acry insertional mutant. These in vivo effects are congruent with in vitro data showing that blue, yellow, and red light, but not far-red light, are absorbed by the neutral radical state of flavin in aCRY. The aCRY neutral radical is formed following blue light absorption of the oxidized flavin. Red illumination leads to conversion to the fully reduced state. Our data suggest that aCRY is a functionally important blue and red light-activated flavoprotein. The broad spectral response implies that the neutral radical state functions as a dark form in aCRY and expands the paradigm of flavoproteins and cryptochromes as blue light sensors to include other light qualities

Attenuated Aβ42 Responses to Low Potency γ-Secretase Modulators Can Be Overcome for Many Pathogenic Presenilin Mutants by Second-generation Compounds*

Sequential processing of the β-amyloid precursor protein by β- and γ-secretase generates the amyloid β-peptide (Aβ), which is widely believed to play a causative role in Alzheimer disease. Selective lowering of the pathogenic 42-amino acid variant of Aβ by γ-secretase modulators (GSMs) is a promising therapeutic strategy. Here we report that mutations in presenilin (PS), the catalytic subunit of γ-secretase, display differential responses to non-steroidal anti-inflammatory drug (NSAID)-type GSMs and more potent second-generation compounds. Although many pathogenic PS mutations resisted lowering of Aβ42 generation by the NSAID sulindac sulfide, the potent NSAID-like second-generation compound GSM-1 was capable of lowering Aβ42 for many but not all mutants. We further found that mutations at homologous positions in PS1 and PS2 can elicit differential Aβ42 responses to GSM-1, suggesting that a positive GSM-1 response depends on the spatial environment in γ-secretase. The aggressive pathogenic PS1 L166P mutation was one of the few pathogenic mutations that resisted GSM-1, and Leu-166 was identified as a critical residue with respect to the Aβ42-lowering response of GSM-1. Finally, we found that GSM-1-responsive and -resistant PS mutants behave very similarly toward other potent second-generation compounds of different structural classes than GSM-1. Taken together, our data show that a positive Aβ42 response for PS mutants depends both on the particular mutation and the GSM used and that attenuated Aβ42 responses to low potency GSMs can be overcome for many PS mutants by second generation GSMs