Plant Biology Seminar

Metabolite Binding of Plant Cryptochromes

Cryptochrome (cry) blue light photoreceptors have important roles in the regulation of plant development. Their photocycle includes redox changes of their FAD chromophore, which is fully oxidized in the dark state and semi-reduced in the signalling-active lit state. The two Arabidopsis thaliana cryptochromes cry1 and cry2 and the plant-type cryptochrome CPH1 from Chlamydomonas rheinhardtii bind ATP and other nucleotides. ATP binding affects the photocycle of these photoreceptors and causes structural alterations. However, the exact regions that undergo structural changes have not been defined, and most importantly, it is not known whether ATP binding affects the biological activity of these photoreceptors in planta. Here we present studies on the effect of ATP on Arabidopsis cry1 and cry2. Both proteins show a high affinity for ATP with KDs in the µM range. Binding of ATP and other adenines promotes photoreduction of the FAD chromophore in vitro and caused structural changes, particularly in α-helix 21, which links the photosensory domain with the C-terminal extension. cry2 mutants (cry2Y399A, cry2Y399F) were constructed that are unable or less able, respectively, to bind ATP. Expression of the mutant photoreceptors in Arabidopsis null cry2 mutant plants shows that they retain some biological activity, which is, however, lower than that of the wild type. Our results indicate that binding of ATP to cry2 and most likely to other plant-type cryptochromes is not essential but boosts the formation of the signalling state and the biological activity.

Invited Speaker: Alfred Batschauer (University Marburg)
Date: Monday, February 5
Time: 4:30 pm
Place: HHU, lecture hall 6F
The PhD students will meet with the speaker after the seminar for the „PBS Lounge with Pizza and Beer" in the AG Feldbrügge seminar room (26.12.01).