The ethylene-forming enzyme (EFE) is a non-heme Fe(II), 2-oxoglutarate (2OG)-, and L-arginine (L-Arg)-dependent oxygenase that catalyzes two reactions (i) oxidative decarboxylation of 2OG, forming succinate and CO2, coupled with C5 hydroxylation of L-Arg and (ii) the decomposition of 2OG to ethylene plus three molecules of CO2/bicarbonate. The L-Arg hydroxylation reaction of EFE follows a well-established mechanism of dioxygen activation and ferryl-based hydrogen atom abstraction leading to substrate hydroxylation as seen in other Fe(II)/2OG oxygenases. However, the generation of ethylene by cleaving three C-C bonds of 2OG is unique to EFE. The ethylene-forming mechanism is suggested to diverge from the hydroxylation mechanism during the dioxygen activation process. Regardless of the current success in experimental and computational studies of EFE, the atomistic and electronic structure determinants for the L-Arg hydroxylation vs. the ethylene-formation mechanism remain unclear. We apply an integrated molecular dynamic (MD) and combined quantum mechanics, and molecular mechanics (QM/MM) approach to test the hypothesis that a synergy between a specific conformation of the primary substrate L-Arg and the coordination mode of cosubstrate 2OG defines the reaction path toward ethylene formation or L-Arg hydroxylation. We assess whether L-Arg exhibits the two conformations in the dynamics of the catalytically important EFE●Fe(III)●OO.-●2OG●L-Arg complex and then investigate the role of the two L-Arg conformations and the two 2OG coordination modes on the dual reactions of EFE. Finally, using the Fe center's molecular orbitals analysis, we explore the electronic structure variation in the metallocenter that leads to ethylene formation vs. L-Arg hydroxylation. Overall, our results highlight the atomistic and electronic structure factors that can be influenced to improve the ethylene yield in EFE.

Structural determinants for ethylene formation and L-Arginine hydroxylation reaction mechanisms in the ethylene-forming enzyme

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.