While fluorescence has long been used to tag biological molecules, a new technology developed at Yale allows researchers to use tiny fluorescent probes to rapidly detect and identify protein interactions within living cells while avoiding the biological disruption of existing methods, according to a report in Nature Chemical Biology.
Proteins are commonly tagged using variants of the “green fluorescent protein” (GFP), but these proteins are very large and are often toxic to live cells. They also tend to aggregate, making them difficult to work with and monitor. This new methodology uses the fluorescence emitted by a small molecule, rather than a large protein. It gives researchers a less disruptive way to capture images of the intricate contacts between folded regions of an individual protein or the partnerships between proteins in a live cell.
“Our approach bypasses many of the problems associated with fluorescent proteins, so that we can image protein interactions in living cells,” said senior author Alanna Schepartz, the Milton Harris Professor of Chemistry, and Howard Hughes Medical Institute Professor at Yale. “Using these molecules we can differentiate alternative or misfolded proteins from those that are folded correctly and also detect protein partnerships in live cells.”
Each protein is a three-dimensional structure created by “folding” its linear chain of amino acids. Usually only one shape “works” for each protein. The particular shape a protein takes depends on its amino acids and on other processes within the cell.
Schepartz and her team devised their new tagging system using small molecules, called “profluorescent” biarsenal dyes. These molecules easily enter cells and become fluorescent when they bind to a specific amino acid tag sequence within a protein. While these compounds have been used for about a decade to bind single proteins, this is the first time they have been used to identify interactions between proteins.