Fusing proteins together as they interact means their actions can be analysed
Biochemists have discovered that proteins prefer to work together, forming supramolecular complexes that perform many of the functions within a cell.
These protein-protein interactions are dynamic and the supramolecular complexes are often fairly short-lived, making them difficult to study. A team of molecular biologists in Germany has come up with a potential solution to this problem, by incorporating photoactivatable amino acids into cellular proteins.
This novel analytical method is actually an updated version of commonly used techniques for investigating protein-protein interactions. This involves incorporating a compound or unnatural amino acid into specified proteins. These compounds then link together when the proteins interact, permanently joining the proteins together and allowing them to be analysed using gel electrophoresis-based separation techniques.
The problem with current methods is they tend to be fairly complex, requiring a range of specially-generated compounds to incorporate the chemical or amino acid into the protein. This has limited their usefulness in studies.
Researchers at the Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, realised that the process could be made simpler if they could get the cell’s own protein synthesis machinery to incorporate the linking compounds into proteins. To do this, they modified the natural amino acids leucine and methionine by adding a photoactivatable diazirine ring, which gives a reactive carbene on exposure to ultraviolet (UV) light.
The researchers discovered that these modified amino acids were naturally taken up by cellular proteins, in place of normal leucine and methionine, such that a 500-amino acid protein would contain 3-4 modified amino acids. Furthermore, the modified amino acids didn’t seem to harm the cells, although they did grow more slowly and didn’t seem to interfere with protein function.
Shining UV light on the cells causes the modified amino acids to fuse together, and the researchers showed that this caused interacting proteins to link together.
M Suchanek et al, Nature Methods, 2005, 2, 261