Biology subjects

Hanic, M.

Publications and source records attributed to Hanic, M..

3 recordsLinked to original sources

bioRxiv2024

European Robin Cryptochrome-4a Associates with Lipid Bilayers in an Ordered Manner, Fulfilling a Molecular-Level Condition for Magnetoreception

Since the middle of the 20th century, long-distance avian migration has been known to rely partly on the geomagnetic field. However, the underlying sensory mechanism is still not fully understood. Cryptochrome 4a (ErCry4a), found in European Robin (Erithacus rubecula), a night-migratory songbird has been suggested to be a magnetic sensory molecule. It is sensitive to external magnetic fields via the so-called radical-pair mechanism. ErCry4a is primarily located in the outer segments of the double cone photoreceptor cells in the eye, which contain stacked and highly ordered membranes that could facilitate the anisotropic attachment of ErCry4a needed for magnetic compass sensing. Here, we investigate possible interactions of ErCry4a with a model membrane that mimics the lipid composition of outer segments of vertebrate photoreceptor cells by using experimental and computational approaches. Experimental results show that the attachment of ErCry4a to the membrane could be controlled by the physical state of lipid molecules (average area per lipid) in the outer leaflet of the lipid bilayer. Furthermore, polarization modulation infrared reflection absorption spectroscopy allowed us to determine the conformation, motional freedom, and average orientation of the - helices in ErCry4a in a membrane-associated state. Atomistic molecular dynamics studies supported the experimental results. A [~]1000 kcal mol-1 decrease in the interaction energy as a result of ErCry4a membrane binding was determined compared to cases where no protein binding to the membrane occurred. At the molecular level, the binding seems to involve negatively charged carboxylate groups of the phosphoserine lipids and the C-terminal residues of ErCry4a. Our study reveals a potential direct interaction of ErCry4a with the lipid membrane and discusses how this binding could be an essential step for ErCry4a to propagate a magnetic signal further and thus fulfill a role as a magnetoreceptor.

biophysics↗

bioRxiv2023

A marine cryptochrome with an inverse photo-oligomerization mechanism

Cryptochromes (CRYs) are a structurally conserved but functionally diverse family of proteins that can confer unique sensory properties to organisms. In the marine bristle worm Platynereis dumerilii, its light receptive cryptochrome L-CRY (PdLCry) allows the animal to discriminate between sunlight and moonlight, an important requirement for synchronizing its lunar cycle-dependent mass spawning. Using cryo-electron microscopy, we show that in the dark, PdLCry adopts a dimer arrangement observed neither in plant nor insect CRYs. Intense illumination disassembles the dimer into monomers. Structural and functional data suggest a mechanistic coupling between the light-sensing flavin adenine dinucleotide chromophore, the dimer interface, and the C-terminal tail helix, with a likely involvement of the phosphate binding loop. Taken together, our work establishes PdLCry as a CRY protein with inverse photo-oligomerization with respect to plant CRYs, and provides molecular insights into how this protein might help discriminating the different light intensities associated with sunlight and moonlight.

biochemistry↗

bioRxiv2023

Dimerisation of European robin cryptochrome 4a

Homo-dimer formation is important for the function of many proteins. Although dimeric forms of cryptochromes (Cry) have been found by crystallography and were recently observed in vitro for European robin Cry4a, little is known about the dimerisation of avian cryptochromes and the role it could play in the mechanism of magnetic sensing in migratory birds. Here we present a combined experimental and computational investigation of the dimerisation of robin Cry4a resulting from covalent and non-covalent interactions. Experimental studies using native mass spectrometry, mass spectrometric analysis of disulphide bonds, chemical cross-linking and photometric measurements show that disulphide-linked dimers are routinely formed, the most likely cysteines being C317 and C412. Computational modelling and molecular dynamics simulations were used to generate and assess a number of possible dimer structures. The relevance of these findings to the proposed role of Cry4a in avian magnetoreception is discussed.

biochemistry↗