Revealing critical functional enzymes in anammox nitrogen removal and rate-limiting step in catalytic pathways: Insight into metaproteomics and density functional theory

Abstract

To reveal the key enzymes in the nitrogen removal pathway and to further elucidate the mechanism of the catalytic reaction, this study utilized metaproteomics combined with molecular dynamics and density functional theory calculation. K. stuttgartiensis provided the proteins up to 88.37 % in the anammox-based system. Hydrazine synthase (HZS) and hydrazine dehydrogenase (HDH) accounted for 15.94 % and 3.45 % of the total proteins expressed by K. stuttgartiensis, thus were considered as critical enzymes in the nitrogen removal pathway. The process of HZSγ binding to NO with lowest binding free energy of −4.91 ± 1.33 kJ/mol. The reaction catalyzed by HZSα was calculated to be the rate-limiting catalyzing step, because it transferred the proton from NH3 to ·OH by crossing an energy barrier of up to 190.29 kJ/mol. This study provided molecular level insights to enhance the performance of nitrogen removal in anammox-based system.