The flavinyl transferase ApbE of Pseudomonas stutzeri matures the NosR protein required for nitrous oxide reduction.
Zhang, L., Trncik, C., Andrade, S.L., Einsle, O.(2016) Biochim Biophys Acta 1858: 95-102
- PubMed: 27864152 
- DOI: https://doi.org/10.1016/j.bbabio.2016.11.008
- Primary Citation of Related Structures:  
5MGY - PubMed Abstract: 
The copper-containing enzyme nitrous oxide reductase (N 2 OR) catalyzes the transformation of nitrous oxide (N 2 O) to dinitrogen (N 2 ) in microbial denitrification. Several accessory factors are essential for assembling the two copper sites Cu A and Cu Z , and for maintaining the activity. In particular, the deletion of either the transmembrane iron-sulfur flavoprotein NosR or the periplasmic protein NosX, a member of the ApbE family, abolishes N 2 O respiration. Here we demonstrate through biochemical and structural studies that the ApbE protein from Pseudomonas stutzeri, where the nosX gene is absent, is a monomeric FAD-binding protein that can serve as the flavin donor for NosR maturation via covalent flavinylation of a threonine residue. The flavin transfer reaction proceeds both in vivo and in vitro to generate post-translationally modified NosR with covalently bound FMN. Only FAD can act as substrate and the reaction requires a divalent cation, preferably Mg 2+ that was also present in the crystal structure. In addition, the reaction is species-specific to a certain extent.
Organizational Affiliation: 
Institute for Biochemistry, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg im Breisgau, Germany.