Importance of the iron-sulfur component and of the siroheme modification in the resting state of sulfite reductase.

Importance of the iron-sulfur component and of the siroheme modification in the resting state of sulfite reductase.
J Inorg Biochem. 2019 Nov 18;203:110928
Authors: Brânzanic AMV, Ryde U, Silaghi-Dumitrescu R
Abstract
The active site of sulfite reductase (SiR) consists of an unusual siroheme-Fe4S4 assembly coupled via a cysteinate sulfur, and serves for multi-electron reduction reactions. Clear explanations have not been demonstrated for the reasons behind the choice of siroheme (vs. other types of heme) or for the single-atom coupling to an Fe4S4 center (as opposed to simple adjacency or to coupling via chains consisting of more than one atom). Possible explanations for these choices have previously been invoked, relating to the control of the spin state of the substrate-binding (siro)heme iron, modulation of the trans effect of the (Fe4S4-bound) cysteinate, or modulation of the redox potential. Reported here is a density functional theory (DFT) investigation of the structural interplay (in terms of geometry, molecular orbitals and magnetic interactions) between the siroheme and the Fe4S4 center as well as the importance of the covalent modifications within siroheme compared to the more common heme b, aiming to verify the role of the siroheme modification and of the Fe4S4 cluster at the SiR active site, with focus on previously-formulated hypotheses (geometrical/sterics, spin state, redox and electron-transfer control). A calibrati...

Source: Journal of Inorganic Biochemistry - November 17, 2019 Category: Biochemistry Authors: Brânzanic AMV, Ryde U, Silaghi-Dumitrescu R Tags: J Inorg Biochem Source Type: research