Abstract
We have developed [2.2.1]azabicyclic vinyl sulfone reagents that simultaneously enable cysteine-selective protein modification and introduce a handle for further bioorthogonal ligation. The reaction is fast and selective for cysteine relative to other amino acids that have nucleophilic side-chains, and the formed products are stable in human plasma and are moderately resistant to retro Diels-Alder degradation reactions. A model biotinylated [2.2.1]azabicyclic vinyl sulfone reagent was shown to efficiently label two cysteine-tagged proteins, ubiquitin and C2Am, under mild conditions (1-5 equiv. of reagent in NaPi pH 7.0, room temperature, 30 min). The resulting thioether-linked conjugates were stable and retained the native activity of the proteins. Finally, the dienophile present in the azabicyclic moiety on a functionalised C2Am protein could be fluorescently labelled through an inverse electron demand Diels-Alder reaction in cells to allow selective apoptosis imaging. The combined advantages of directness, site-specificity and easy preparation mean [2.2.1]azabicyclic vinyl sulfones can be used for residue-specific dual protein labelling/construction strategies with minimal perturbation of native function based simply on the attachment of an [2.2.1]azabicyclic moiety to cysteine.
Highlights
We present strained [2.2.1]azabicyclic vinyl sulfones as efficient and versatile reagents for residue-speci c dualEdge Article protein labelling
The dienophile present in the azabicyclic moiety on a functionalised C2A domain of Synaptotagmin-I (C2Am) protein could be fluorescently labelled through an inverse electron demand Diels–Alder reaction in cells to allow selective apoptosis imaging
Having shown the chemoselectivity of 1 towards cysteine residues, we studied the stability of the formed thioether because we were concerned by some rDA reports of cleavage with similar bicyclic systems.[22,31,32,33,34]
Summary
We present strained [2.2.1]azabicyclic vinyl sulfones as efficient and versatile reagents for residue-speci c dualEdge Article protein labelling. A model biotinylated [2.2.1]azabicyclic vinyl sulfone reagent was shown to efficiently label two cysteine-tagged proteins, ubiquitin and C2Am, under mild conditions
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