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Title: Tyrosine or Tryptophan? Modifying a Metalloradical Catalytic Site by Removal of the Cys-Tyr Cross-Link in the galactose 6-oxidase homologue GlxA
Authors: Chaplin, Amanda K
Bernini, Caterina
Sinicropi, Adalgisa 
Basosi, Riccardo 
Worrall, Jonathan A R
Svistunenko, Dimitri A
Keywords: EPR spectra simulations; TRSSA; Tyr-Cys motif; copper-radical oxidases; through-protein radical transfer
Issue Date: 2017
Project: None 
The concerted redox action of a metal ion and an organic cofactor is a unique way to maximize the catalytic power of an enzyme. An example of such synergy is the fungal galactose 6-oxidase, which has inspired the creation of biomimetic copper oxidation catalysts. Galactose 6-oxidase and its bacterial homologue, GlxA, possess a metalloradical catalytic site that contains a free radical on a covalently linked Cys-Tyr and a copper atom. Such a catalytic site enables for the two-electron oxidation of alcohols to aldehydes. When the ability to form the Cys-Tyr in GlxA is disrupted, a radical can still be formed. Surprisingly, the radical species is not the Tyr residue but rather a copper second-coordination sphere Trp residue. This is demonstrated through the introduction of a new algorithm for Trp-radical EPR spectra simulation. Our findings suggest a new mechanism of free-radical transfer between aromatic residues and that the Cys-Tyr cross-link prevents radical migration away from the catalytic site.
ISSN: 1433-7851
DOI: 10.1002/anie.201701270
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