A collaboration of chemists, biologists, and physicists centered at the Universities of Oldenburg in Germany and Oxford in the United Kingdom, for the first time, has been collecting evidence that the magnetic sense of migratory songbirds like European birds is based on a particular light-sensitive protein in the eye.
SciTechDaily reported humans see the world surrounding them with five senses, including vision, taste, smell, hearing, and touch. Many other animals can sense as well the magnetic field of Earth.
In the study, the researchers showed that the protein cryptochrome 4, found in the retinas of birds, is "sensitive to magnetic fields" and could well be the long-searched magnetic sensor.
Doctoral student Jingjing Xu in Henrik Mouritsen's research group in Oldenburg, the study's first author, took a pivotal step toward this successful work.
Photoactive Molecule Produced for the First Time
For the first time, Xu produced this photoactive molecule after extracting genetic code for the possibly magnetically sensitive cryptochrome 4 in night-migratory European robins in great quantities using microbial cell cultures.
As specified in this report, Christiane Timmel's and Stuart Mackenzie's teams in Oxford then used a great range of magnetic resonance and innovative optical spectroscopy approaches to examine the protein and present its pronounce sensitivity to magnetic fields.
In addition, the team deciphered the mechanism as well, by which such a sensitivity arises, another essential advancement.
Mouritzen explained electrons that can move within the molecule following blue-light activation are playing a vital role.
Cryptochrome and Tryptophan
The study, "Magnetic sensitivity of cryptochrome 4 from a migratory songbird", published in the journal Nature, described proteins like cryptochrome, as explained in the National Library of Medicine, comprise chains of amino acids-robin cryptochrome 4 comprises about 527 of them.
Peter Hore of Oxford and Ilia Solov'yov, a physicist of Oldenburg, performed quantum mechanical calculations, supporting the notion that four of the more than 527, identified as tryptophans, are vital for the molecules' magnetic properties.
Based on their computations, electrons hop from the tryptophan to the next, generating "radical pairs," which have magnetic sensitivity.
For such a finding to be experimentally proven, the Oldenburg team generated slightly altered versions of the robin cryptochrome, in which each tryptophan, in turn, was replaced by amino acid to block the electrons' movement.
Cryptochrome 4 Expressed from Chickens and Pigeons
The team from Oldenburg expressed cryptochrome 4 as well, from chickens and pigeons. When examined in Oxford, these species' proteins, which are not migrating, exhibit similar photochemistry of the migratory robin, although they appear strikingly less sensitive magnetically.
Mouritsen said they think such results are quite essential since they exhibit for the first time that a molecule from a migratory bird's visual apparatus is sensitive to magnetic fields.
However, he added, this is not definitive evidence that cryptochrome 4 is the magnetic sensor the researchers are looking for.
In all experiments, the study authors examined isolated proteins in the laboratory. The magnetic fields used were sturdier as well, compared to the magnetic field of Earth.
He stressed, it consequently still needs to be shown that this is occurring in the birds' eyes. Such studies, he added, are not yet possible, technically.
Nevertheless, the study investigators think the proteins involved could substantially be more sensitive in their native environs.
In cells in the retina, perhaps, the proteins are fixed and aligned, augmenting their sensitivity to the magnetic field's direction.
Furthermore, they like to be linked as well to other proteins that could intensify the sensory signals. The researchers are currently searching for these as yet not known interaction partners.
According to Hore, if they can prove that cryptochrome 4 is the magnetic sensor, they would have demonstrated an essentially quantum mechanism, making animals sensitive to environmental motivations a million times weaker compared to previously perceived possible.
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