Glowing Nobel Prize

The Nobel Prize for Chemistry this year went to three scientists for the discovery and development of the glowing jellyfish protein green fluorescent protein (GFP). GFP underpins much of modern biochemistry specifically because of its power as an absorption and emission marker that lights up the behaviour of biological molecules.

In 1962 organic chemist Osamu Shimomura identified the form and function of the remarkably bright protein that gives the jellyfish Aequorea Victoria its eerie, yet beautiful glow. His discovery has since become one of the most important tools used in modern biological sciences. It allows researchers to engineer cells and even whole organisms to express this fluorescent protein under specific physiological or chemical conditions. This then allows them to watch processes that were previously invisible, such as the development of nerve cells in the brain or the spread of cancer cells. The development of GFP was pioneered by the two scientists that share the 2008 Prize with Osamu Shimomura, Roger Tsien and Martin Chalfie.

Specifically, Martin Chalfie demonstrated how GFP could be used as a fluorescent genetic tag for various biological phenomena, having coloured six individual cells in the transparent roundworm Caenorhabditis elegans using GFP in his early experiments. Roger Tsien contributed to our general understanding of how GFP fluoresces and extended the colour palette available to biological researchers to allow them to label various proteins and cells with all the colours of the rainbow. This development allows scientists to track several different biological processes simultaneously.

Without the chemistry of GFP, post-genomic era scientists would lack the experimental tools giving them access to quantitative and experimentally well-defined monitoring at the molecular level of biochemical changes taking place within the cell and between cells in all living systems.

The whole GFP "family" of proteins that emerged from the work of this year's Nobel chemists allows researchers to monitoring in real time and in space myriad phenomena including gene expression, protein localization and dynamics, protein-protein interactions, cell division, chromosome replication and organization, intracellular transport pathways, pH changes and ion transport, organelle inheritance and biogenesis, and much more. All key processes and understanding of which is critical to an understanding of life, development, growth and disease.

At the core of the archetypal GFP from Aequorea Victoria lies a glowing chromophore, a chemical group comprising a tri-peptide unit that gives light to the jellyfish and to any organism in which the protein is genetically engineered and then expressed. The native protein from the jellyfish contains 238 amino acids, but it is residues 65-67 (Ser-Tyr-Gly) in the GFP sequence that work together to spontaneously form the fluorescent chromophore p-hydroxybenzylideneimidazolinone.

Tsien reported the excitation spectrum of GFP fluorescence as having a dominant maximum at approximately 400 nm and a much smaller maximum at about 470 nm. Its emission spectrum has a sharp maximum at about 505 nm and a shoulder around 540 nm.

Spectral specifics aside, key to the potency of GFP as a chemical tool of molecular biology then lies in this "automatic" aspect of the functioning of GFP. Unlike many other proteins that might be engineered into an experimental organism, GFP requires only a supply of molecular oxygen as an activation trigger and no co-enzymes nor any auxiliary biochemical factors.

Moreover, as Chalfie demonstrated GFP is generally non-toxic and can be expressed to high levels in different organisms with little effect on their physiology. Indeed, when the GFP gene is spliced with that of another protein, the expressed protein of interest retains its normal activity and GFP retains its fluorescence. GFP and the growing number of related variants being added to the molecular toolkit by researchers means it can be used to visualize almost any biochemical process.

Today, there are many novel variants of GFP with improved or complementary properties in relation to those of GFP from A victoria. "The GFP revolution in the biological sciences has been greatly accelerated by a rapid parallel development of quantitative light microscopy, electronics, computational power and molecular modelling of intra- and inter-cellular processes with systems-biology approaches."