Side chain motions affect functional radical transfer in ribonucleotide reductase.

What is it about?

This paper evidences side chain motions of an essential tyrosine that affect the requisite radical transfer for catalytic activity of ribonucleotide reductase (RNR). To demonstrate this, we studied the E. coli RNR, and trapped radicals on pathway via incorporation of the unnatural amino acid 3-amino tyrosine (NH2Y), and the trapped radical environment was examined by a high resolution 2D EPR technique called HYSCORE. Additionally, the dynamics (kinetics) of conformationally mobile radical transfer were investigated by photochemically generating a pathway radical, and following subsequent radical transfer.

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Why is it important?

This study offers a paradigm shift in our understanding of radical transfer via proton-coupled electron transfer (PCET) in RNR, and furthermore, within soft materials like proteins. The subtle but observable conformational motions of a single amino acid residue dramatically affect proton transfer rates due to the strict distance dependence. Our results suggest that static structures do not provide sufficient information to predict PCET processes accurately, and require dynamic considerations.