Substrate turnover in class Ia ribonucleotide reductase (RNR) requires reversible radical transport across two subunits over 35 Å, which occurs by a multistep proton-coupled electron-transfer mechanism. Using a photooxidant-labeled β2 subunit of Escherichia coli class Ia RNR, we demonstrate photoinitiated oxidation of a tyrosine in an α2:β2 complex, which results in substrate turnover. Using site-directed mutations of the redox-active tyrosines at the subunit interface, Y356F(β) and Y731F(α), this oxidation is identified to be localized on Y356. The rate of Y 356 oxidation depends on the presence of Y731 across the interface. This observation supports the proposal that unidirectional PCET across the Y356(β)-Y731(α)-Y 730(α) triad is crucial to radical transport in RNR.
ASJC Scopus subject areas
- General Chemistry
- Colloid and Surface Chemistry