A shared mechanistic pathway for pyridoxal phosphate–dependent arginine oxidases

Dr. Marc Garcia-Borràs (IQCC) is part of an international multidisciplinary research team led by Prof. Katherine Ryan (University of British Columbia, Canada) that has recently published a new study in PNAS entitled “A shared mechanistic pathway for pyridoxal phosphate–dependent arginine oxidases”. Pyridoxal phosphate (PLP)-dependent enzymes rarely react with oxygen, but an emerging group of PLP- and oxygen-dependent enzymes oxidize L-arginine. Two types of oxidases are known: hydroxylases and desaturases. The mechanism by which molecular oxygen is activated by the PLP organic cofactor for oxidation reactions remains poorly understood.

This study demonstrates that arginine desaturases have a minor hydroxylase activity; through X-ray crystallographic, mutagenesis, spectroscopic, and computational studies it is shown that the reaction mechanism involves two rounds of single-electron transfer to oxygen and superoxide rebound, ultimately producing a conjugated hydroperoxyl intermediate. Water can attack to give a hydroxylated product and release H2O2; without water present the intermediate can be deprotonated, giving a desaturated product and H2O2 instead. The precise positioning of a water molecule in the active site is proposed to control the final reaction outcome. The proposed mechanism provides a unified framework to understand how oxygen can be activated by PLP-dependent enzymes for oxidation of arginine and elucidates a shared mechanistic pathway and intertwined evolutionary history for arginine desaturases and hydroxylases. This study sets the stage for engineering these enzymes to catalyze new oxidative reactions.

Scheme of PLP- and oxygen-dependent arginine oxidase reactivities

The study was recently published in the Proceedings of the National Academy of Sciences of the United States of America:

E.R. Hoffarth, K. Caddell Haatveit, E. Kuatsjah, G.A. MacNeil, S. Saroya, C.J. Walsby, L.D. Eltis, K.N. Houk, M. Garcia-Borràs, and K.S. Ryan
“A shared mechanistic pathway for pyridoxal phosphate–dependent arginine oxidases”
Proc Natl Acad Sci USA 2021, 118, e2012591118
DOI: 10.1073/pnas.2012591118

Girona, Oct. 5, 2021
For more information: gestor.iqcc@gmail.com