Proximity Histidine Labeling by Umpolung Strategy Using Singlet Oxygen

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Abstract
While electrophilic reagents for histidine labeling have been developed, we report an umpolung strategy for histidine functionalization. A nucleophilic small molecule, 1-methyl-4-arylurazole, selectively labeled histidine under singlet oxygen (1O2) generation conditions. Rapid histidine labeling can be applied for instant protein labeling. Utilizing the short diffusion distance of 1O2 and a technique to localize the 1O2 generator, a photocatalyst in close proximity to the ligand-binding site, we demonstrated antibody Fc-selective labeling on magnetic beads functionalized with a ruthenium photocatalyst and Fc ligand, ApA. Three histidine residues located around the ApA binding site were identified as labeling sites by liquid chromatography–mass spectrometry analysis. This result suggests that 1O2-mediated histidine labeling can be applied to a proximity labeling reaction on the nanometer scale.
Funding Information
  • Tokyo Biochemical Research Foundation
  • Japan Society for the Promotion of Science (15H05490, 19H02848, 20H04699)

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