LAMAs in control
A tool to control the cellular localization of proteins enables to probe their biological function.
Green fluorescent protein (GFP) is a widely used tool for visualizing and probing cellular processes at the molecular level. Scientists at the Max Planck Institute for Medical Research, the European Molecular Biology Laboratory (EMBL) as well as the University Hospital in Heidelberg now introduce a family of molecular ‘switches’ – so called LAMAs – to control the cellular localization of GFP fusion proteins. The results, published in Nature Methods this week, demonstrates the utility of these engineered nanobodies to study fundamental biological processes.
Scientists worldwide strive towards understanding biological processes by identifying and studying proteins involved in cellular mechanisms. For convenient visualization of a protein of interest, the protein can be fused to a green fluorescent protein (GFP fusion protein). While the protein of interest would otherwise remain ‘invisible’, the GFP acts as a fluorescent marker. It permits indirect observation of protein through light microscopy-based methods. Together with collaborators, researchers at the MPI for Medical Research present an exciting new tool to control the localization of GFP fusion proteins on demand.
Introducing switchable nanobodies
The so-called “ligand-modulated antibody fragments” – LAMAs – are engineered nanobodies. They consist of an antibody fragment and a ‘switch’ that can be flipped on or off by addition of a small molecule. “We take advantage of the high selectivity and specificity of nanobodies and combine it with the fast temporal control offered by using small molecules as a switch,” says Dr. Helen Farrants, first author and former PhD student in the Department of Chemical Biology at the MPI for Medical Research.
The switch enables to control the localization of target proteins via their fusion protein GFP. Without the small molecule present, the LAMA is bound to the GFP fusion protein (target). By adding specific localization sequences to the LAMA, the whole complex can be directed to different parts of the cell. Upon adding the small molecule trimethoprim (TMP) the conformation of the LAMA changes and it can no longer bind to the target. The target is then free to return to its original location and purpose in the cell. This on-off switching is completely reversible and can also be repeated many times.
One strategy – many applications
“It is a new mechanism to control the system you are studying – and countless scientists are already working with GFP-tagged proteins,” says Dr. Farrants. “This should make the tool very popular in the life science community.”
The team also demonstrated that the approach can be used to switch nanobodies which target other proteins than GFP. This should open the door towards a wide variety of different LAMAs. The work also demonstrated how the approach can be applied to other nanobodies, further ensuring that the LAMAs will proliferate and prosper.