A Charge-Reversal Point Mutation Completely Depletes Flavin Chromophore from European Robin Cryptochrome 4a Protein
Jingjing Xu1,2,3, Emil Sjulstok Rasmussen4, Francis Berthias1
1Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark.
The Journal of Physical Chemistry Letters
|February 16, 2026
Summary
European robin Cry4a protein requires specific electrostatic interactions for flavin adenine dinucleotide (FAD) binding. A mutation altering charge at residue 356 prevents FAD binding, impacting bird navigation.
Area of Science:
- Biophysics
- Structural Biology
- Avian Navigation
Background:
- Cryptochrome 4a (Cry4a) is a light-sensitive protein crucial for avian magnetoreception.
- Flavin adenine dinucleotide (FAD) is essential for Cry4a's magnetic sensitivity.
- The mechanism of FAD binding in avian Cry4a is not well understood.
Purpose of the Study:
- To elucidate the molecular mechanism of FAD binding in European robin Cry4a.
- To identify key residues and interactions involved in FAD cofactor binding.
Main Methods:
- Site-directed mutagenesis was used to create a R356E mutant of European robin Cry4a.
- FAD binding affinity was assessed for both wild-type and mutant proteins.
Main Results:
- A point mutation (R356E) completely abolished FAD binding in European robin Cry4a.
- Electrostatic interactions involving arginine 356 are critical for FAD binding.
Conclusions:
- Electrostatic forces are the primary drivers of FAD binding in European robin Cry4a.
- This finding provides crucial structural insights into FAD binding in Cry4 proteins.
- Advances understanding of the biophysical basis of bird magnetoreception.
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