Coniferyl Alcohol Radical Detection by the Dirigent Protein At DIR6 Monitored by EPR

Plant dirigent proteins (DIRs) control the stereoselectivity of the monolignol coniferyl alcohol radical coupling. The main mechanistic hypothesis on this chemo‐ and stereoselective reaction invokes a binding of coniferyl alcohol radical substrates in the dirigent protein active site so that only one enantiomeric form can be produced. We have studied the influence of the Arabidopsis thaliana At DIR6 protein on the transient coniferyl alcohol radical by EPR. Herein, we show that At DIR6 stabilizes coniferyl alcohol radicals prior to directing their coupling towards the formation of (−)‐pinoresinol.