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Physical Chemistry

Ligands Let Copper Click Inside Cells

Bulky amine ligands detoxify copper in cellular click reactions, enabling azide-alkyne cycloadditions in the cytoplasm without hurting cells

by Stu Borman
September 29, 2014 | A version of this story appeared in Volume 92, Issue 39

CYTOPLASMIC ENABLERS
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Credit: Adapted from Nat. Commun.
Tris(triazolylmethyl)amine-based ligands enable copper-catalyzed azide-alkyne cycloaddition reactions to be carried out in the interior of cells without toxicity; proteins are blue rectangles with azide group, and the reagent in the center is a fluorescent marker (green star) with a terminal alkyne group.
A diagram showing a copper-catalyzed azide-alkyne cycloaddition reaction in a cell interior.
Credit: Adapted from Nat. Commun.
Tris(triazolylmethyl)amine-based ligands enable copper-catalyzed azide-alkyne cycloaddition reactions to be carried out in the interior of cells without toxicity; proteins are blue rectangles with azide group, and the reagent in the center is a fluorescent marker (green star) with a terminal alkyne group.

Copper-catalyzed click chemistry, an azide-alkyne cycloaddition reaction, is often used to label biomolecules on cell surfaces to study their functions. But it is not used in the cell cytoplasm because copper can be toxic to cells. A process that uses bulky ligands to stabilize and detoxify copper, enabling the reaction to be used inside living bacteria without hurting them, has now been developed by Jing Zhao of Nanjing University, in China; Peng Wu of Albert Einstein College of Medicine of Yeshiva University, in New York City; Peng R. Chen of Peking University, in China; and coworkers (Nat. Commun. 2014, DOI: 10.1038/ncomms5981). The researchers used tris(triazolylmethyl)amine-based ligands to corral copper as it helps fluorescently mark proteins with pH-dependent conformations in the cell cytoplasm and periplasm. This approach enabled them to determine pH gradients across the Escherichia coli cytoplasmic membrane. They also measured the E. coli transmembrane potential and determined the force required to move protons across the bacterial inner membrane under normal and acid-stress conditions.

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