Shedding Light On the Mechanism of Magnetic Sensing In Birds

For some time, a collaboration of biologists, chemists and physicists centered at the Universities of Oldenburg (Germany) and Oxford (UK) have been gathering evidence suggesting that the magnetic sense of migratory birds such as European robins is based on a specific light-sensitive protein in the eye. In the current edition of the journal Nature, this team demonstrate that the protein cryptochrome 4, found in birds' retinas, is sensitive to magnetic fields and could well be the long-sought magnetic sensor. Phys.Org reports: First author Jingjing Xu, a doctoral student in Henrik Mouritsen's research group in Oldenburg, took a decisive step toward this success. After extracting the genetic code for the potentially magnetically sensitive cryptochrome 4 in night-migratory European robins, she was able, for the first time, to produce this photoactive molecule in large quantities using bacterial cell cultures. Christiane Timmel's and Stuart Mackenzie's groups in Oxford then used a wide range of magnetic resonance and novel optical spectroscopy techniques to study the protein and demonstrate its pronounced sensitivity to magnetic fields.

The team also deciphered the mechanism by which this sensitivity arises -- another important advance. "Electrons that can move within the molecule after blue-light activation play a crucial role," explains Mouritsen. Proteins like cryptochrome consist of chains of amino acids: robin cryptochrome 4 has 527 of them. Oxford's Peter Hore and Oldenburg physicist Ilia Solov'yov performed quantum mechanical calculations supporting the idea that four of the 527 -- known as tryptophans -- are essential for the magnetic properties of the molecule. According to their calculations, electrons hop from one tryptophan to the next generating so-called radical pairs which are magnetically sensitive. To prove this experimentally, the team from Oldenburg produced slightly modified versions of the robin cryptochrome, in which each of the tryptophans in turn was replaced by a different amino acid to block the movement of electrons. Using these modified proteins, the Oxford chemistry groups were able to demonstrate experimentally that electrons move within the cryptochrome as predicted in the calculations -- and that the generated radical pairs are essential to explain the observed magnetic field effects. Hore says "if we can prove that cryptochrome 4 is the magnetic sensor we will have demonstrated a fundamentally quantum mechanism that makes animals sensitive to environmental stimuli a million times weaker than previously thought possible."

I wonder if they will patent this?

[Greeneland]

Maybe I will patent the toll-booth-in-the-sky they will need to collect from the bird population.

Tryptophan

[phantomfive]

Tryptophan, it puts you to sleep, it senses magnetic fields, is there nothing it can't do?

Protein is just half the story

[phantomfive]

Finding the protein is just half the story. Another big question is how that information is transferred to the brain. It sounds like these birds can literally "see" magnetic fields.

Re:

[Marquis de Pattymelt]

Sure, it's called the "electromagnetic spectrum", but fucking magnets, how do they work?

Re:

[phantomfive]

I don't know. Gravity makes even less sense to me.

Re:Protein is just half the story

[kahizonaki]

They talk about that in the summary. They say that after absorbing blue light, the electrons in that channel protein can move. This will likely result in modulating the probability of channel opening (which in turns allows ions to flow into or out of the cell, changing its membrane potential). The change in membrane potential will cause an increase or decrease in neurotransmitter vesicle exocytosis rates...which will eventually propogate to the brain via retinal ganglion cells (I actually didn't read in detail -- is this a special type of ganglion cell? In which case it will directly modulate the probability of action potential induction).