Selective modification of native proteins in live cells is one of the central challenges in recent chemical biology. As a unique bioorthogonal approach, ligand-directed chemistry recently emerged, but the slow kinetics limits its scope. Here we successfully overcome this obstacle using N-acyl-N-alkyl sulfonamide as a reactive group. Quantitative kinetic analyses reveal that ligand-directed N-acyl-N-alkyl sulfonamide chemistry allows for rapid modification of a lysine residue proximal to the ligand binding site of a target protein, with a rate constant of ~104 M−1 s−1, comparable to the fastest bioorthogonal chemistry. Despite some off-target reactions, this method can selectively label both intracellular and membrane-bound endogenous proteins. Moreover, the unique reactivity of N-acyl-N-alkyl sulfonamide enables the rational design of a lysine-targeted covalent inhibitor that shows durable suppression of the activity of Hsp90 in cancer cells. This work provides possibilities to extend the covalent inhibition approach that is currently being reassessed in drug discovery.

Lipids play crucial roles as the structural elements, signalling molecules, and material transporters in cells. However, the functions and dynamics of lipids within cells remain unclear because of a lack of methods to selectively label lipids in specific organelles and trace their movement by live-cell imaging. We describe here a technology for the selective labelling and fluorescence micro/nanoscopic imaging of phosphatidylcholines in target organelles. The approach involves the metabolic incorporation of azido-choline followed by a spatially limited bioorthogonal reaction, which enables the visualization and quantitative analysis of interorganelle lipid transport in live cells. Most importantly, with live-cell imaging, we obtained direct evidence that the autophagosome membrane originates from the endoplasmic reticulum. This method is simple and robust, and thus powerful for real-time tracing of interorganelle lipid trafficking.

Protein functions are tightly regulated by their subcellular localization in live cells, and quantitative evaluation of dynamically altered proteomes in each organelle should provide valuable information. Here, we describe a novel method for organelle-focused chemical proteomics using spatially limited reactions. In this work, mitochondria-localizable reactive molecules (MRMs) were designed that penetrate biomembranes and spontaneously concentrate in mitochondria, where protein labeling is facilitated by the condensation effect. The combination of this selective labeling and liquid chromatography-mass spectrometry (LC-MS) based proteomics technology facilitated identification of mitochondrial proteomes and the profile of the intrinsic reactivity of amino acids tethered to proteins expressed in live cultured cells, primary neurons and brain slices. Furthermore, quantitative profiling of mitochondrial proteins whose expression levels change significantly during an oxidant-induced apoptotic process was performed by combination of this MRMs-based method with a standard quantitative MS technique (SILAC: stable isotope labeling by amino acids in cell culture). The use of a set of MRMs represents a powerful tool for chemical proteomics to elucidate mitochondria-associated biological events and diseases.

Reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) can inflict damage to biomolecules under oxidative stress and also act as signaling molecules at physiological levels. Here we developed a unique chemical tool to elucidate the biological roles of ROS using both fluorescence imaging and conditional proteomics. H2O2-responsive protein labeling reagents (Hyp-L) were designed to selectively tag proteins under the oxidative conditions in living cells and tissues. The Hyp-L signal remained even after sample fixation, which was compatible with conventional immunostaining. Moreover, Hyp-L allowed proteomic profiling of the labeled proteins using a conditional proteomics workflow. The integrative analysis enabled the identification of ROS generation and/or accumulation sites with a subcellular resolution. For the first time, we characterized that autophagosomes were enriched with H2O2 in activated macrophages. Hyp-L was further applied to mouse brain tissues and clearly revealed oxidative stress within mitochondria by the conditional proteomics.