How marine bristleworms use a special protein to distinguish sunlight from moonlight

In a recent publication in Natural communicationsa joint research team from the Johannes Gutenberg University Mainz (JGU), the University of Cologne and the University of Oldenburg presented their findings on the function of an atypical cryptochrome protein (Cry).

These proteins are found in various organisms and are often involved in biological processes controlled by light. The marine bristleworm Platynereis dumerilii, for example, uses a special Cry protein called L-Cry to distinguish between sunlight and moonlight as well as between different phases of the moon.

This is essential for the worms to synchronize their reproduction with the full moon phase via an internal monthly calendar, also called the circalunar clock. The Cologne researchers used their university’s electron cryomicroscopy platform to visualize the three-dimensional structure of the L-Cry protein under different lighting conditions.

The results of these structural analyses, together with those of biochemical research undertaken primarily at the University of Mainz, revealed that, in the dark, L-Cry adopts a so-called dimeric arrangement consisting of two subunits linked by a stable connection. , while it is subjected to intensive conditions. Lighting similar to sunlight, it disassembles into its subunits or monomers.

It is not only the spatial arrangement of the two subunits in the dark that is unusual and matches an arrangement not previously observed in other Cry proteins. The direction of light-induced changes is also unusual since for other Cry proteins only the reverse process has been described, i.e. from monomer arrangements in the dark to dimer arrangements or superior oligomers to light.

The research team was also able to identify key structural features of the protein that are important for this unusual behavior. Additionally, knowledge of the three-dimensional structure allowed researchers to introduce targeted mutations into the L-Cry protein to further characterize its function as a photoreceptor.

“Our findings could explain how L-Cry manages to distinguish between sunlight and moonlight: intense sunlight always activates both subunits of the dimer simultaneously, which initiates its breakdown into individual subunits . However, significantly weaker moonlight only statistically activates one of the two subunits.”, explained Professor Eva Wolf from the JGU Institute of Molecular Physiology, who led the study at the University from Mainz.

The study results highlight the uniqueness of L-Cry among the highly diverse Cry proteins, with their wide range of functions. They are also thought, for example, to be sensor proteins in the perception of the Earth’s magnetic field in birds.

First steps in decoding the molecular processes of the circalunar clock

“Working with light-sensitive proteins is always a challenge,” said Hong Ha Vu, a doctoral student in Professor Eva Wolf’s JGU research group and a major contributor to the study.

“When preparing L-Cry proteins for analysis, we must perform all experimental processes in the dark or under specifically defined red light conditions to avoid unintended preactivation of these highly light-sensitive proteins. functional characterization of L-Cry, it is also necessary to use lighting conditions similar to natural underwater sunlight and moonlight lighting of the type that hairworms encounter in their natural habitat.

“Only then can we compare the specific properties of L-Cry in its role as a receptor for sunlight and moonlight with those of other cryptochromes.”

Professor Eva Wolf added: “Our research has provided important new insights into how this very unusual receptor for sunlight and moonlight works. Furthermore, our molecular structural and mechanistic insights into L-Cry function have opened future avenues of research that should help us gain further insight. the still largely unknown molecular processes involved in the synchronization of the circalunar clock with the phases of the moon.