Green Fluorescent Protein (GFP) is a remarkable biological tool that has revolutionized various scientific fields. This protein, originally discovered in the jellyfish Aequorea victoria, possesses the unique ability to emit a vibrant green light. Its discovery and development earned a Nobel Prize, underscoring its profound impact on research. GFP’s inherent fluorescent property makes it invaluable for visualizing processes within living organisms.
How GFP Lights Up
GFP’s ability to “light up” stems from a natural phenomenon called fluorescence. This process involves the absorption of light at one specific wavelength, known as excitation, and the subsequent emission of light at a longer wavelength. When GFP absorbs light, its internal structure, specifically a chromophore formed by three amino acids, becomes energized, temporarily elevating it to a higher energy state.
The chromophore within GFP, composed of a serine-tyrosine-glycine tripeptide, undergoes a post-translational modification involving cyclization and oxidation to become fluorescent. After absorbing energy, this excited chromophore quickly returns to its stable, lower energy state by releasing the excess energy as light, which is observed as the characteristic green glow of GFP.
The Specific Light for GFP
To activate GFP and observe its green fluorescence, researchers must illuminate it with light at specific wavelengths. Wild-type GFP from Aequorea victoria exhibits a primary excitation peak around 395 nanometers (nm), which falls within the ultraviolet to violet light spectrum. It also has a smaller, secondary excitation peak at approximately 475 nm, corresponding to blue light.
Researchers utilize specialized light sources, such as lasers or lamps, calibrated to emit light at these specific wavelengths. For instance, enhanced GFP (EGFP) has been engineered to have a single, stronger excitation peak at 488 nm, aligning well with commonly available laboratory equipment and maximizing fluorescence intensity.
Where GFP Shines in Science
GFP’s unique excitation and emission properties make it a valuable tool across diverse scientific disciplines. It is widely employed as a reporter gene, allowing researchers to visualize when and where specific genes are expressed within cells or organisms. By fusing the GFP gene to a gene of interest, scientists can observe the production of proteins and track their movement and localization inside living cells.
This non-invasive tracking capability has advanced fields such as cell biology, enabling the study of cellular functions like protein translation and DNA replication. In neuroscience, GFP helps visualize specific cell types and track neuronal connections. It is also used in drug discovery to monitor drug efficacy and toxicity, and in environmental science to assess toxicity levels.