Quick – can you tell where north is? Animals as diverse as sea turtles, birds, worms, butterflies and wolves can, thanks to sensing Earth’s magnetic field.
But the magnet-sensing structures inside their cells that allow them to do this have evaded scientists – until now.
A team led by Can Xie’s at Peking University in China has now found a protein in fruit flies, butterflies and pigeons that they believe to be responsible for this magnetic sense.
“It’s provocative and potentially groundbreaking,” says neurobiologist Steven Reppert of the University of Massachusetts who was not involved in the work. “It took my breath away.”
There used to be two competing theories about magnetic sense: some thought it came from iron-binding molecules, others thought it came from a protein called cryptochrome, which senses light and has been linked to magnetic sense in birds.
Xie’s group was the first to guess these two were part of the same system, and has now figured out how they fit together.
“This was a very creative approach,” says Reppert. “Everyone thought they were two separate systems.”
Xie’s team first screened the fruit fly genome for a protein that would fit a very specific bill.
The molecule had to bind iron, it had to be expressed inside a cell instead of on the cell membrane and do so in the animal’s head – where animals tend to sense magnetic fields – and it also had to interact with cryptochrome.
“We found one [gene] fit all of our predictions,” says Xie. They called it MagR and then used techniques including electron microscopy and computer modelling to figure out the protein’s structure.
They found that MagR and cryptochrome proteins formed a cylinder, with an inside filling of 20 MagR molecules surrounded by 10 cryptochromes.
The researchers then identified and isolated this protein complex from pigeons and monarch butterflies.
In the lab, the proteins snapped into alignment in response to a magnetic field. They were so strongly magnetic that they flew up and stuck to the researchers’ tools, which contained iron. So the team had to use custom tools made of plastic.
The team hasn’t yet tried to remove the MagR protein from an animal like a fruit fly to see if it loses its magnetic sense, but Xie believes the proteins work the same way in a living animal.
Although this protein complex seems to form the basis of magnetic sense, the exact mechanism is still to be figured out.
One idea is that when an animal changes direction, the proteins may swing around to point north, “just like a compass needle,” says Xie. Perhaps the proteins’ movement could trigger a connected molecule, which would send a signal to the nervous system.
Journal reference: Nature Materials, DOI: 10.1038/nmat4484
Thanks to Kebmodee for bringing this to the It’s Interesting community.