Saturday, May 20, 2023

Targeted Proximity-Labelling of Protein Tyrosines via Flavin-Dependent Photoredox Catalysis with Mechanistic Evidence for a Radical-Radical Recombination Pathway

Taylor O. Hope, Tamara Reyes-Robles, Keun Ah Ryu, Steven Mauries, Nicole Removski, Jacinthe Maisonneuve, Rob C. Oslund,* Olugbeminiyi O. Fadeyi,* and Mathieu Frenette*

Chemical Science, 2023

DOI: 10.1039/D3SC00638G

Flavin-based photocatalysts such as riboflavin tetraacetate (RFT) serve as a robust platform for light-mediated protein labelling via phenoxy radical-mediated tyrosine-biotin phenol coupling on live cells. To gain insight into this coupling reaction, we conducted detailed mechanistic analysis for RFT-photomediated activation of phenols for tyrosine labelling. Contrary to previously proposed mechanisms, we find that the initial covalent binding step between the tag and tyrosine is not radical addition, but rather radical-radical recombination. The proposed mechanism may also explain the mechanism of other reported tyrosine-tagging approaches. Competitive kinetics experiments show that phenoxyl radicals are generated with several reactive intermediates in the proposed mechanism—primarily with the excited riboflavin-photocatalyst or singlet oxygen—and these multiple pathways for phenoxyl radical generation from phenols increase the likelihood of radical-radical recombination.



Rapid, potent, and persistent covalent chemical probes to deconvolute PI3Kα signaling

Lukas Bissegger,  Theodora A. Constantin,  Erhan Keles,  Luka Raguž,   Isobel Barlow-Busch,  Clara Orbegozo,   Thorsten Schaefer,  Valentina...