Glowing Proteins On The Spot

By tweaking a bacterial enzyme, Massachusetts Institute of Technology researchers have developed a new way to fluorescently label proteins at specific locations inside living cells (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0914067107). Although some chemical tags exist for this purpose, most notably green fluorescent protein, they can interfere with protein function or have other drawbacks such as toxicity or lack of selectivity. To add to the tagging tool kit, Alice Y. Ting and coworkers mutated a lipoic acid ligase enzyme from Escherichia coli. Ting’s team previously used this enzyme to label cell-surface proteins. Now, the mutant ligase binds to a blue fluorescent coumarin dye designed to enter cells. It attaches the glowing dye cargo to a 13-amino acid recognition sequence that the researchers engineer into the protein of choice. Ting and coworkers used their system to track the cytoskeletal protein actin and later used it to specifically label subsets of proteins in certain cellular locales such as the nucleus. With further improvements in speed and sensitivity, this method could illuminate protein trafficking between neuronal synapses and other compartments, the researchers write. The group has filed for a patent on the technology.