Protein of the Week: GFP
Osamu Shimomura, his colleagues, and his family spent the better part of several summers of collecting jellyfish in order to determine the compounds that caused their bioluminescence:
The figure above is taken from Osamu Shimomura's Nobel lecture.
In the process of isolating and characterizing the blue compound, aequorin, Shimomura and his colleague Frank Johnson found a second compound that fluoresced green. A decade later when Shimomura began to characterize green fluorescent protein (GFP), he found that its fluorescence resulted from an unusual chromophore that forms spontaneously from amino acids within the core of the protein.
The figure above is taken from Figure 2 from Heim et al., PNAS (1994) 91: 12501-04.
Enhanced GFP excitation (cyan, peak at 488 nm) and emission (green, peak at 512 nm) spectra.
Martin Chalfie and Roger Tsien shared the 2008 Nobel Prize in Chemistry with Osamu Shimomura for their work in making GFP the workhorse that it is today in biochemistry and cell biology. Chalfie and colleagues were the first to fuse the gene for GFP to that of other proteins or gene promoter sequences to see where in a cell a protein would be expressed or where in an organism a gene is turned on.
z-series of GFP expressed in a cell
Through both random and directed mutagenesis, Tsien and colleagues have developed a toolbox of fluorescent proteins that cover the entire visual spectrum.
Bacterial expression of tdTomato, eCFP, and eGFP
Tsien's proteins made possible the labeling of multiple proteins within a sample, each with its own fluorophore. A wonderful example can be seen in the "brainbow" pictured below:
from Figure 4 in Livet, et al., Nature (2007) 450: 56-63