Modulation of Y [subscript 356] Photooxidation in E. Coli Class Ia Ribonucleotide Reductase by Y [subscript 731] Across the α [subscript 2] :β [subscript 2] Interface

Abstract

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 β[subscript 2] subunit of Escherichia coli class Ia RNR, we demonstrate photoinitiated oxidation of a tyrosine in an α[subscript 2]:β[subscript 2] complex, which results in substrate turnover. Using site-directed mutations of the redox-active tyrosines at the subunit interface, Y[subscript 356]F(β) and Y[subscript 731]F(α), this oxidation is identified to be localized on Y[subscript 356]. The rate of Y[subscript 356] oxidation depends on the presence of Y[subscript 731] across the interface. This observation supports the proposal that unidirectional PCET across the Y[subscript 356](β)–Y[subscript 731](α)–Y[subscript 730](α) triad is crucial to radical transport in RNR.