Green fluorescent protein

Green fluorescent protein
Core Anatomical, the first view in the company gallery Iridian (2026): green fluorescent protein, PDB entry 1EMA, rising from the pupil of an animated eye
Identifiers
Organism	Aequorea victoria (crystal jelly)
Symbol	GFP
PDB structure	1EMA (S65T variant, 1996); 1GFL (wild type, 1996)
Properties
Subunits	238 amino acids, about 27 kDa
Function	Converts the blue light of aequorin into green light

Green fluorescent protein (GFP) is a protein from the jellyfish Aequorea victoria that glows green when it is lit with blue or ultraviolet light. Because it makes its own light-emitting group from three of its amino acids, with no help except oxygen, its gene can be joined to the gene of almost any other protein in almost any organism, and the cell will make a glowing copy of that protein. Biologists use it to watch where proteins go and when genes switch on inside living cells. The 2008 Nobel Prize in Chemistry went to Osamu Shimomura, Martin Chalfie and Roger Tsien "for the discovery and development of the green fluorescent protein".^[1]

Shimomura was looking for the source of the jellyfish's light. Working with Frank Johnson at Friday Harbor, Washington, he purified aequorin, a protein that gives off blue light when it binds calcium, from tens of thousands of jellyfish caught from the docks. In their paper of 1962 he and his co-authors noted a second protein in the extracts that glowed green under ultraviolet light.^[2] In the living animal the two work in sequence: aequorin's energy passes to GFP, and the jellyfish's rim shines green.

The natural protein has 238 amino acids. They fold into a cylinder of eleven strands, a shape called a beta-can, with a helix running down its center. In the middle of the helix, three amino acids, serine 65, tyrosine 66 and glycine 67, react with one another and with oxygen to form the chromophore, the part that absorbs and emits light. The can shields it from the water outside. The wild protein absorbs most strongly at 395 nanometers, with a smaller peak at 475, and emits at 509, in the green.^[1]

The first crystal structure, published in Science in September 1996 by S. James Remington's group with Tsien's, was of a modified version in which serine 65 had been replaced by threonine. That is entry 1EMA in the Protein Data Bank.^[3] The structure of the natural protein followed about a month later.^[4]

Douglas Prasher cloned and sequenced the gene in 1992.^[5] His funding ran out before he could test it in other organisms, and he sent copies to laboratories that asked. In 1994 Chalfie's group showed that the gene alone made bacteria and the nematode Caenorhabditis elegans glow, proving that no jellyfish enzyme was needed to build the chromophore.^[6] In 1995 Tsien's group reported the change of serine 65 to threonine, which moved the main absorption peak to 488 nanometers, matched the filters already in fluorescence microscopes, and made the protein much brighter.^[7] Tsien's laboratory went on to make proteins of other colors.

Joined to the gene of another protein, GFP shows where that protein goes in a living cell, and placed under the control of a gene's switch it shows when and where the gene is on. Variants of other colors, and related proteins from corals, allow several labels in one cell; in the "Brainbow" mice of 2007, random mixtures of three or four fluorescent proteins gave neighboring neurons distinguishable colors. The protein has also reached art. In 2000 the artist Eduardo Kac presented GFP Bunny, a white rabbit named Alba that carried the gene and was said to glow green under blue light.

Only three people may share a Nobel Prize. When the 2008 prize was announced, Prasher was working as a courtesy shuttle driver at a car dealership in Huntsville, Alabama. Chalfie and Tsien invited him to the ceremony in Stockholm, and he later joined Tsien's laboratory as a research associate.^[8]

In July 2026 Molecular Reality Corporation published Iridian, a gallery titled "197 Views of the Seeing Eye". Each view is a twenty-second animation in which an eye opens, holds with small darting movements, and closes while a protein emerges from the pupil and turns. In the first view, Core Anatomical, the protein is green fluorescent protein, entry 1EMA, drawn atom by atom as colored spheres.^[9] Entry 1EMA is the threonine variant. The gallery's baseline eye releases the protein as improved in Tsien's laboratory in 1995, which no jellyfish makes.

The gallery was published a month before the company's front page was cut to the sentence "everybody's racing to build the brain, we're building the eye" and an animation of an eye releasing lysozyme.^[10] The company has not explained its choice of either protein. GFP is the molecule that let biologists see inside living cells. The idea is set out in the article The Seeing Eye.

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