Structures of the sulfite detoxifying F420-dependent enzyme from Methanococcales

Abstract

Methanogenic archaea are main actors in the carbon cycle but are sensitive to reactive sulfite. Some methanogens use a sulfite detoxification system that combines an F420H2-oxidase with a sulfite reductase, both of which are proposed precursors of modern enzymes. Here, we present snapshots of this coupled system, named coenzyme F420-dependent sulfite reductase (Group I Fsr), obtained from two marine methanogens. Fsr organizes as a homotetramer, harboring an intertwined six-[4Fe–4S] cluster relay characterized by spectroscopy. The wire, spanning 5.4 nm, electronically connects the flavin to the siroheme center. Despite a structural architecture similar to dissimilatory sulfite reductases, Fsr shows a siroheme coordination and a reaction mechanism identical to assimilatory sulfite reductases. Accordingly, the reaction of Fsr is unidirectional, reducing sulfite or nitrite with F420H2. Our results provide structural insights into this unique fusion, in which a primitive sulfite reductase turns a poison into an elementary block of life.

High-throughput genetics enables identification of nutrient utilization and accessory energy metabolism genes in a model methanogen

“…The M. maripaludis Dsr (MMP_RS00450) contains a siroheme and two 4Fe-4S clusters but no F 420 H 2 oxidase (Fsr-N) fusion (34, 37). However, decreased mutant fitness for the native dsr in M. maripaludis fitness assays with sulfite and thiosulfate suggests it still has a role in sulfite detoxification.…”

Structural and biochemical elucidation of class I hybrid cluster protein natively extracted from a marine methanogenic archaeon

“…An alternative enzyme or pathway would be necessary. Nitrite reduction to ammonia can be performed by methanogens [e.g., by the F 420 -dependent sulfite/nitrite reductase ( Jespersen et al, 2023 )]. The enzymatic reduction of nitrite may, in theory, be a source of NO, similar to the nitrate reducers.…”

“…Methanothermococcus thermolithotrophicus strain DSM 2095 was obtained from the Deutsche Sammlung von Mikroorganismen und Zellkulturen (DSMZ, Braunschweig, Germany). The archaeon was grown on ammonia and sulphate in a fermenter at 65°C, as described in Jespersen et al (2023) .…”

Differences in the regulation mechanisms of the glutamine synthetase from methanogenic archaea unveiled by structural investigations

“…thermolithotrophicus (DSM 2095) cells were obtained from the Leibniz Institute DSMZ -German Collection of Microorganisms and Cell Cultures (Braunschweig, Germany). Cells were grown in a minimal medium as described in Jespersen et al 44 . Anaerobic cultivation of M. thermolithotrophicus was performed in a fermenter with NH4Cl and SO4 2as described in Jespersen et al 2022 45 with slight modifications, or in a fermenter with N2 and SO4 2as described in Maslać et al 2022 40 .…”