Birds use the magnetic field of the Earth to navigate during their annual migratory travel. The possible mechanism to explain the biophysics of this compass sense involves electron transfers within the photoreceptive protein cryptochrome. A study (Qin et al., 2016) claimed that the sensitivity to changes in the magnetic field is enhanced by a coupling to an iron rich polymer complex which couples to multiple cryptochromes. For the iron sulphur clusters to participate in the compass sense, they either need to donate an electron to a specific tryptophane in the cryptochome or accept an electron from the flavin adenine dinucleotide (FAD) co-factor in the cryptochrome. To validate the claim, it is needed to independently reconstruct this complex and describe its interaction with Drosophila melanogaster cryptochromes. The polymer complex consists of iron sulphur containing assembly ISCA1 protein monomers with internally bound iron sulphur clusters and simultaneously binds ten cryptochromes, shown in Fig. 1. Homology modelling and crystal packing structure of the used proteins is used to construct the large cryptochrome-ISCA1 complex, which reveals that the iron sulphur clusters are too far away to participate in any electron transfer whatsoever.
The dynamic behaviour of the cryptochrome-ISCA1 complex is monitored to investigate both the time-evolution of the distance between the co-factors involved in electron transfer, and the interaction energy between cryptchrome and ISCA1, to see if the cryptochromes stick to ISCA1 and if they do so consistently along the rod. As seen in Fig. 2, the interaction energy is non-homologues along the ISCA1-rod it, revealing that the complex does likely not exist in the proposed form, and the large distance between the cofactors participating in electron factors rules out that this cryptochrome interaction has any relevance to magnetoreception. A more interesting interaction partner to cryptochrome is still sought after.