A new method for the quick addition of small labeling molecules promises to simplify studies tracking the localization and dynamics of cell-surface proteins without interfering with cellular function (see Nature Methods).
Bigger isn't better when it comes to molecular tags. Visualization tools like green fluorescent protein (GFP) have proven invaluable in a wide variety of studies, but tacking on an entire protein adds bulk that can interfere with the very processes one is trying to observe. Smaller tags exist, but many of these also suffer from flaws such as rapid dissociation or excessive background.
Alice Ting and her colleagues have developed a different approach, taking advantage of a bacterial protein, BirA, which normally engineers the addition of a molecule called biotin to what is known as an acceptor peptide (AP) sequence. BirA can also be used to tack on biotin derivatives, and Ting's group developed a modified biotin with a unique chemical group not found in mammalian cells. This group becomes the platform for a specific chemical reaction that irreversibly attaches appropriately designed fluorescent tag molecules. Virtually any cell-surface protein containing the AP sequence can be labeled by this two-step process, which takes about twenty minutes.
Ting's group initially demonstrates that this labeling is highly specific and capable of detection that even outshines other fluorescence-based strategies; further tests with an AP-tagged cell-surface receptor protein reveal similar specificity and clarity, and show that tagging does not appear to interfere with the function of the receptor protein.
This technology offers an effective and less disruptive strategy for marking cell surface proteins, an approach Ting and her colleagues hope will soon be expanded for use in proteins inside the cell as well.
Alice Y. Ting
Massachusetts Institute of Technology, Cambridge, MA, USA.
Tel: +1 617 452 2021
Also available online.
(C) Nature Methods press release.
Message posted by: Trevor M. D'Souza