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Biological Chemistry

Glowing Proteins On The Spot

Mutant bacterial enzyme labels proteins site-specifically inside live cells

by Carmen Drahl
June 7, 2010 | A version of this story appeared in Volume 88, Issue 23

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.

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Credit: Katharine White and Tao Uttamapinant
A mutant ligase enzyme facilitates protein labeling at specific sites inside cells, such as the nucleus (top), or cytosol (bottom), as shown in these confocal microscopy images.
Credit: Katharine White and Tao Uttamapinant
A mutant ligase enzyme facilitates protein labeling at specific sites inside cells, such as the nucleus (top), or cytosol (bottom), as shown in these confocal microscopy images.

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