Tyrosyl Radical in the W164Y Mutant of P. eryngiiVersatile Peroxidase: an EPR and DFT/PCM Study

Versatile peroxidases (VP) constitute a new class of high redox potential fungal enzymes that are able to degrade lignin and large substrate molecules. These enzymes catalyze the oxidation of substrates at an exposed tryptophan radical formed by a long-range electron transfer mechanism to heme following the activation by H2O2. In a previous paper, it was demonstrated using electron paramagnetic resonance (EPR) and electron-nuclear double resonance experiments on wild-type VP that Trp164 was the radical site and that it was in a hydrogen-bonded neutral form. In this paper, the W164Y variant is analyzed and it is shown that also the variant is able to form the so-called Compound I (VPI) in the form of protein radical, although in different yields with respect to the wild type. The X-band EPR experiments in combination with density functional theory/polarizable continuum model calculations show that the W164Y mutant is able to form a neutral radical on Tyr164 residue, after activation by H2O2, but in contrast to Trp164, tyrosine is not expected to be hydrogen bonded.