Theoretical investigation of the reaction mechanism of THP oxidative rearrangement catalysed by BBOX

Abstract

γ-Butyrobetaine hydroxylase (BBOX) is a non-heme Fe^II/2OG dependent enzyme that is able to perform two different kinds of catalytic reactions on 3-(2,2,2-trimethylhydrazinium) propionate (THP) to produce distinct catalytic products. Although the structure of BBOX complexed with THP has been resolved, the details of its catalytic mechanism are still elusive. In this study, by employing molecular dynamics (MD) simulations and density functional theory (DFT) calculations, the mechanism of the THP oxidative rearrangement reactions catalysed by BBOX was investigated. Our calculations revealed how the enzyme undergoes a conformational conversion to initiate the catalytic reactions. In the first catalytic step, BBOX performs hydrogen abstraction from the substrate THP as a common non-heme iron enzyme. Due to the structure of the substrate stabilizing the radical species and polarizing the adjacent N–N bond, in the next step, THP takes the pathway for N–N bond homolysis but not regular hydroxyl rebounding. The cleaved ammonium radical could either react with the hydroxyl group on the iron centre of the enzyme or recombine with the other cleaved fragment of the substrate to generate the rearranged product. This study revealed the catalytic mechanism of BBOX, detailing how the enzyme and the substrate regulated the hydroxyl rebound process to generate various products.