Extraordinary Proteins. Extreme lifestyles sometimes require sensing the earth's magnetic field. Trytophan and aspartic acid residues may be key to an organism's ability to pick up where it is relative to the earth's poles.

Birds, turtles, butterflies and other animals migrate with the help of the compasses built into their bodies. Little is known about the mechanistic nature of these compasses, and to fill the gap in knowledge, researchers at the theoretical and computation biophysics group at the University of Illinois at Urbana-Champaign describe a systems based on a flavoprotein known to process light for entraining circadian cycles, but now perhaps also should be known as the seat of these organism's ability to sense magnetic fields[1]. ^[1].

Molecular Tour:

Illia Solov'yov and Klau Schulten of the Theoretical and Computational Biophysics group at the University of Illinois at Urbana-Champaign think that the FAD factor and just several residues of a crytochrome protein is all it takes to register the magnetic field of the earth. The they describe involves the . When light in the blue range hits the FAD factor it becomes excited, with the excitement diffused over its . Then, one of the three neighboring aspartic acid residues donates a hydrogen proton from its hydroxyl group. The FAD factor then receives an electron from the neighboring tryptophan, from the tryptophan's nitrogen atom (shown in halo). The proton and electron that FAD received are attached to one of the nitrogen atoms on its ring (shown in halos). Next, this tryptophan received an electron from its , and then the second tryptophan received an electron from its neighbor, a third tryptophan. Finally, the third tryptophan loses a proton to a neighboring element. At the end of this reaction, both the FAD factor and the third tryptophan residue contain a unpaired electron. The ability of the FAD factor to transfer back the electron received from the first trytophan to the third tryptophan is effected by the magnetic field of the Earth, because the two electons can exist in two spin states, parallel and antiparallel, with interconversion between states partly determined by the earth's magnetic force, and only the parallel state compatible with back transfer of the electron from FAD to trytophan. Thus, the speed which with FAD transfers back its donated electron is affected by the earth's magnetic field, and that speed can be registered by the brain as a proxy for where it lies relative to the earth's magnetic field.