Magnetic field effects on the structure and molecular behavior of pigeon iron-sulfur protein.

Pigeon iron-sulfur (Fe-S) cluster assembly 1 homolog (clISCA1) is a target protein for research into the biomagnetoreception mechanism, as the clCRY4/clISCA1 oligomer, a complex composed of the columnar clISCA1 oligomer and the magnetosensor candidate protein cryptochrome-4 (clCRY4) oligomer, tends to orient itself along weak magnetic fields, such as geomagnetic fields, under blue light. To obtain insight into the magnetic orientation mechanism of the clCRY4/clISCA1 oligomer, we inspected magnetic field effects on the structure and molecular behavior of clISCA1 by small angle X-ray scattering analysis. The results indicated that the clISCA1 protomer took the Fe-S cluster-bound globular form and unbound rod-like form. The globular clISCA1 protomer assembled to form columnar oligomers, which allowed for the binding of many Fe-S clusters at the interface between clISCA1 protomers. Moreover, the translational diffusion and the columnar oligomerization of clISCA1 were controlled by the external static magnetic field and Fe-S clusters bound to clISCA1. However, the columnar clISCA1 oligomer was not oriented along the external static magnetic field (~1 T) when clCRY4 was not bound to clISCA1. This result indicated that clCRY4 has a function to enhance the magnetic orientational property of clCRY4/clISCA1 oligomer.