We are incentivizing entries in Art in Science by offering a monetary prize – and who doesn’t love a good prize? Specifically speaking, who doesn’t love the Nobel Prize?
In 2008, Martin Chalfie, Osamu Shimomura, and Roger Tsien won the Nobel Prize in Chemistry for the discovery and subsequent development of green fluorescent protein (GFP) as a microbiology tool. A sculpture of the protein entitled “Steel Jellyfish” is on display at Friday Harbor Laboratories in Washington where GFP was discovered.
GFP as a Microbiology Tool
GFP is composed of 238 amino acids, or protein building blocks. These amino acids associated with each other using hydrogen bonding into 11 secondary structures known as beta sheets or beta pleated sheets. These 11 beta pleated sheets form the barrel shape called a beta-can. Because the beta-can shape is very compact, GFP is a relatively stable protein able to withstand temperatures up to 90C and a pH range of 4-12 with little denaturation. Additionally, the beta-can structure gives GFP a low reactivity, which allows scientists to introduce GFP to other types of cells or organisms with few negative effects.
While the mouse expressing GFP is possibly the most iconic animal, many transgenic GFP organisms exists. In addition to a wide varieties of plants and bacteria, transgenic GFP organisms include zebrafish, rabbits, cats and even pigs. Transgenic GFP zebrafish and mice are even available to purchase commercially as pets.
In addition to transgenic organisms expressing solitary GFP, scientists can create sequences that attach GFP to another protein. When this hybrid protein is expressed, GFP acts as a reporter, allowing scientists to track and observe how these proteins behave within the cell or organism.
Fluorescence vs Bioluminescence
GFP was discovered in Aequorea victoria, a species of jellyfish. Also known as the crystal jelly, Aequorea victoria lives in the Pacific waters off the coast of North America. Aequorea victoria is known not only for producing GFP, but also a bioluminescent protein called aequorin.
Bioluminescence occurs from proteins that react with molecules such as calcium ions, oxygen, or ATP, the energy source of living cells. Conversely, fluorescence occurs when the fluorophore, or glowing portion, of proteins or molecules interacts with a specific color of light. Colors of light are characterized by their wavelength and only a very narrow range is absorbed by the fluorophore. The chemical bonds of the fluorophore give the energy from the light a temporary home. The electrons in the chemical bonds are moved to an excited stage with the light energy, and will fall back to their non-excited states and emit light. Since some of the energy from the original light has been dissipated in the chemical bonds, the color of light emitted from the fluorophore is a lower energy color, or higher wavelength. Although there is a range of wavelengths where both the fluorophore excites and the fluorophore emits, there is a narrow range of where there is the maximum amount of excitation and emission occur. Fluorophores exist in many different colors, with different excitation and emission wavelengths, but only GFP is depicted below.
GFP found in jellyfish has a maximum excitation around a wavelength of 395 nanometers and a maximum excitation around 509 nanometers. However, modifications made to GFP by scientists to create enhanced green fluorescent protein (EGFP ) has an excitation at 488 nanometers.
Because fluorophores require a source of light for excitation, one might wonder where the crystal jellyfish finds a light source in the dark waters. The answer is above – aequorin! Aequorin is a bioluminescent protein that interacts with calcium ions to produces a blue light around 365 nanometers. While 365 nanometers is not a perfect match to the 395 nanometer maximum excitation of GFP, it is well within the range of excitation wavelengths for GFP. How amazing is it that this organism not only has proteins to produce light, but also a complementary one to transform light?
From its origins in a humble jellyfish, GFP has revolutionized research in microbiology. As my high school calculus teacher always said, “bright kids see things differently.” Now, thanks to GFP, bright proteins help scientists see things differently.
Until next time.