So what is GFP?
GFP is short for Green Fluorescent Protein
and it's a very big deal
GFP comes from the jellyfish Aequoria victoria
and it's interesting because it's brightly fluorescent green.
This means that scientists can stick GFP on the end of another protein
and see where that protein goes inside a living cell under the microscope.
And because it's quite small at around 27 kDa
sticking it on the end of a much larger protein doesn't really affect protein function that much.
GFP is built out of a barrel with 11 beta strands
and an alpha helix running down the middle.
One of the remarkable things about GFP is that it fluoresces on its own
without the need for any additional enzymes.
This is because of a motif of three important amino acids
in the helix running through the centre of that beta barrel.
Serine 65, Tyrosine 66 and Glycine 67 are so close together
that their chemical groups spontaneously bind together into the GFP chromophore
which is fluorescent whenever there's oxygen around.
But what if you want to show what happens to a bunch of different proteins at the same time?
You'll need more than one colour.
And it turns out that mutating key amino acids around this chromophore motif
can make subtle changes to the fluorescent colour.
This way scientists made yellow and cyan versions of GFP.
But what if you need even more colours?
Well, scientists discovered another fluorescent protein, called dsRed.
This time from the coral Discosoma.
The problem with dsRed is that it forms a tetramer
so sticking them on a protein would make those proteins bunch together in groups of four.
But by making a few key mutations
scientists were able to turn dsRed into a monomer called mRFP
for Monomeric Red Fluorescent Protein,
which was then developed into different colours, such as mOrange, mCherry and mPlum.
So by taking two fluorescent proteins from a jellyfish and coral,
and a lot of painstaking mutations,
scientists have been able to cover the entire colour wheel with fluorescent proteins
and by doing so expanded the horizon of biomedical research.
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