Better explicating the strengths and shortcomings of these models will help refine projections and improve transparency in the years ahead.
Image credit: Witsawat.S.
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Edited by Nicholas J. Turro, Columbia University, New York, NY, and approved September 7, 2007 (received for review July 27, 2007)
Abstract
Dynamic imaging of proteins in live cells is routinely performed by using genetically encoded reporters, an approach that cannot be extended to other classes of biomolecules such as glycans and lipids. Here, we report a Cu-free variant of click chemistry that can label these biomolecules rapidly and selectively in living systems, overcoming the intrinsic toxicity of the canonical Cu-catalyzed reaction. The critical reagent, a substituted cyclooctyne, possesses ring strain and electron-withdrawing fluorine substituents that together promote the [3 + 2] dipolar cycloaddition with azides installed metabolically into biomolecules. This Cu-free click reaction possesses comparable kinetics to the Cu-catalyzed reaction and proceeds within minutes on live cells with no apparent toxicity. With this technique, we studied the dynamics of glycan trafficking and identified a population of sialoglycoconjugates with unexpectedly rapid internalization kinetics.
Footnotes
- ¶To whom correspondence should be addressed at: Department of Chemistry, B84 Hildebrand Hall, #1460, University of California, Berkeley, CA 94720. E-mail: crb{at}berkeley.edu
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Author contributions: J.M.B., J.A.P., S.T.L., N.J.A., P.V.C., I.A.M., and C.R.B. designed research; J.M.B., J.A.P., S.T.L., N.J.A., P.V.C., I.A.M., A.L., and J.A.C. performed research; J.M.B., J.A.P., S.T.L., N.J.A., P.V.C., I.A.M., and C.R.B. analyzed data; and J.M.B. and C.R.B. wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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This article contains supporting information online at www.pnas.org/cgi/content/full/0707090104/DC1.
- Abbreviations:
- DIFO,
- difluorinated cyclooctyne;
- DHFR,
- dihydrofolate reductase;
- SiaNAz,
- azido sialic acid;
- Ac4ManNAz peracetylated,
- N-azidoacetylmannosamine;
- Ac4ManNAc,
- peracetylated N-acetylmannosamine.
- © 2007 by The National Academy of Sciences of the USA
Copper-free click chemistry for dynamic in vivo imaging
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