Copper-free click chemistry for dynamic <i>in vivo</i> imaging

TLDR

Dynamic imaging of proteins in live cells relies on genetically encoded reporters, but this strategy cannot be applied to other biomolecules such as glycans and lipids. The study reports a Cu‑free click chemistry variant that rapidly and selectively labels glycans and lipids in living systems, avoiding the toxicity of Cu‑catalyzed reactions. The method employs a substituted cyclooctyne whose ring strain and fluorine substituents drive a fast [3+2] cycloaddition with metabolically installed azides, achieving kinetics comparable to Cu‑catalyzed reactions within minutes on live cells without toxicity. Using this technique, the authors discovered that certain sialoglycoconjugates internalize rapidly, revealing unexpected dynamics in glycan trafficking.

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.