Origin of Nitric Oxide Reduction Activity in Flavo–Diiron NO Reductase: Key Roles of the Second Coordination Sphere

Abstract

The second coordination sphere constitutes adistinguishing factor in the active site to modulate enzymatic reactivity.T ou nravel the origin of NO-to-N 2 Or eduction activity of non-heme diiron enzymes,herein we report astrong second-coordination-sphere interaction between ac onserved Tyr 197 and the key iron-nitrosyl intermediate of Tm FDP (flavo-diiron protein), which leads to decreased reaction barriers towards N-N formation and N-O cleavage in NO reduction. This finding supports the direct coupling of diiron dinitrosyl as the N-N formation mode in our QM/MM modeling,a nd reconciles the mechanistic controversy of external reduction between FDPs and synthetic biomimetics of the iron-nitrosyls.T his work highlights the application of QM/MM 57 Fe Mçssbauer modeling in elucidating the structural features of not only first, but also second coordination spheres of the key transient species involved in NO/O 2 activation by non-heme diiron enzymes.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Structural basis of RICs iron donation for iron-sulfur cluster biogenesis

“…Mössbauer studies further revealed that one of the iron atoms in the centre is labile, particularly in the mixed-valence Fe(III)-Fe(II) state when compared with the µ-oxo-diferric form Fe(III)-Fe(III) (11). In the reduced form, YtfE Fe(II)-Fe(II) binds NO forming N 2 O (12), which is in line with the intrinsic capacity of di-iron proteins for NO reduction and O 2 activation/reduction (13). Moreover, in YtfE one of the iron ions of the centre is loosely bound with iron dissociation constants in a range of values that enables the YtfE to donate iron to other proteins (11).…”

Structural Basis of RICs Iron Donation for Iron-Sulfur Cluster Biogenesis

“…Mössbauer studies further revealed that one of the iron atoms in the center is labile, particularly in the mixed-valence Fe(III)-Fe(II) state when compared with the µ-oxo-diferric form Fe(III)-Fe(III) (Nobre et al, 2014). In the reduced form, YtfE Fe(II)-Fe(II) binds NO forming N 2 O (Lo et al, 2016), which is in line with the intrinsic capacity of di-iron proteins for NO reduction and O 2 activation/reduction (Lu et al, 2019). Moreover, in YtfE one of the iron ions of the center is loosely bound with iron dissociation constants in a range of values that enables YtfE to donate iron to other proteins (Nobre et al, 2014).…”

A Nonheme Mononuclear {FeNO}7 Complex that Produces N2O in the Absence of an Exogenous Reductant

“…[5a, 8,26] Calculations performed on FDPnor, as well as on synthetic models,suggest that adecrease in the energy barrier for NÀNb ond formation is expected upon enhancement of the nitroxyl (NO À )c haracter of an FeNO center. [27] The weakened N-O vibration of 1681 cm À1 seen for the mononitrosyl form of FDPnor suggests afairly polarized Fe III -NO À unit. [14] This enhanced nitroxyl character was partly attributed to an interaction of the bound NO group with the second Fe II site.T he n(NO) and n(Fe-NO) values for 2 are in excellent agreement with n(NO) = 1681 cm À1 and n(Fe-NO) = 451 cm À1 for deflavo-FDP(NO), [14] and the n(N-O) mode for 2 is indicative of the same degree of NÀOb ond activation.…”