Light, as waves carry energy, is a stimulus input for all forms of life.  Nature has evolved numerous photoreceptors sensitive to all wavelengths of light to react and regulate various essential biological functions. These biological pathways rely on non-visual photoreceptors that involve discrete families of proteins that unexpectedly share photochemical mechanisms and architectures but regulate a wide array of signal transduction responses.

How exactly a wavelength of light that has no mass can be perceived and transformed to a wide range of biochemical outputs is a fundamental question in biology.

As part of our ongoing interest in light sensing mechanisms, our recent research has been focused on a specific subset of photoreceptors in plants, in particular those sensitive to wavelengths between 320–480nm (the visible blue region).

There are three key photoreceptor proteins in plants: phytochromes, phototropins, and the cryptochromes.

Cryptochromes (CRYs) belong to a superfamily of flavoproteins that are present in all life forms. In plants and insects, cryptochromes serve as blue-light photo-receptors and in mammals they play central role in the circadian clock molecular machinery.  The cryptochromes-mediated perception of blue-light in plants generates signals to regulate numerous developmental networks including de-etiolation, photoperiodic control of flowering, root growth, plant height, organ size, stomatal opening, and stress responses. However, the photochemistry, regulation, and light-induced structural changes remained unclear.

In our recent work (Palayam et al., 2021. Communications Biology-Nature), we solved the molecular structure of the photosensory domain of Arabidopsis CRY2 in a tetrameric photoactive state (PDB:6X24).

This study revealed distinct structural elements and critical residues that dynamically partake in photo-induced oligomerization. We suggested an updated model of CRYs photoactivation mechanism as well as the mode of its regulation by interacting proteins. These findings open up new avenues of research and practical applications.