Aryl-alcohol oxidase (AAO) has demonstrated to be an enzyme with a bright future ahead due to its biotechnological potential in deracemisation of chiral compounds, production of bioplastic precursors and other reactions of interest. Expanding our understanding on the AAO reaction mechanisms, through the investigation of its structure-function relationships, is crucial for its exploitation as an industrial biocatalyst. In this regard, previous computational studies suggested an active role for AAO Phe397 at the active-site entrance. This residue is located in a loop that partially covers the access to the cofactor forming a bottleneck together with two other aromatic residues. Kinetic and affinity spectroscopic studies, complemented with computational simulations using the recently developed adaptive-PELE technology, reveal that the Phe397 residue is important for product release and to help the substrates attain a catalytically relevant position within the active-site cavity. Moreover, removal of aromaticity at the 397 position impairs the oxygen-reduction activity of the enzyme. Experimental and computational findings agree very well in the timing of product release from AAO, and the simulations help to understand the experimental results. This highlights the potential of adaptive-PELE to provide answers to the questions raised by the empirical results in the study of enzyme mechanisms.

This work was supported by the EnzOx2 project (H2020-BBI-PPP-2015-720297) of the European Joint Undertaking of Bio-based Industries (http://bbi-europe.eu), the INDOX project (KBBE-2013-7-613549) of the European Seventh Framework Programme, and the NOESIS (BIO2014-56388-R), vMutate (CTQ2016-79138-R) and FLADIMOTEC (BIO2016-75183-P) projects of the Spanish Ministry of Economy and Competitiveness. J.C. acknowledges a FPU fellowship (FPU2012-2041) from the Spanish Ministry of Education, Culture and Sports.

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