Named for the German synthetic-organic chemist Hermann Staudinger, who won the Nobel Prize in 1953 for his pioneering work in polymer chemistry, the Staudinger reaction occurs between an azide and a phosphine, a molecule containing a phosphorus atom. The azide sheds two nitrogen atoms, and a compound called an aza-ylide is formed.
At first glance, this reaction seems ideal for cell engineering: neither phosphines nor azides react with biological molecules, but they react rapidly and with high efficiency with each other, in water and at room temperature. Unfortunately, the resulting aza-ylides fall apart in water almost as easily as they form.
"We asked ourselves if we could create a different kind of aza-ylide that transformed into a stable adduct. Staudinger would have loved the challenge!" Bertozzi and Saxon added an electron-hungry carbohydrate trap to the phosphine, which attaches to the electron-rich aza-ylide and prevents it from falling apart in water, subsequently yielding a stable amide bond.
The technique worked well on the lab bench, but, says Bertozzi, "the cell surface is a lot more demanding than the test tube. Now we had to find a way to install azides on cells."
Partly because azides are small functional groups, they are readily incorporated into sialic-acid residues, sugars that are components of some cell-surface oligosaccharides. When Bertozzi and Saxon fed cultured cells with a sialic-acid precursor containing the azide group, the cells manufactured azide-containing oligosaccharides in abundance and displayed them on their surfaces.
Next a water-soluble phosphine was used to label fluorescent probes to seek out the azide markers. When these chemical probes were allowed to interact with the treated cells, the cells became intensely fluorescent -- the phosphines had found the azides.
"We have developed a useful rea
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Contact: Paul Preuss
paul_preuss@lbl.gov
510-486-6249
DOE/Lawrence Berkeley National Laboratory
15-Mar-2000