Journal Article

Structures of the sulfite detoxifying F 420 -dependent enzyme from Methanococcales

Jespersen, Marion, Wagner, Tristan, Pierik, Antonio J

2023

Overview

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 F H -oxidase with a sulfite reductase, both of which are proposed precursors of modern enzymes. Here, we present snapshots of this coupled system, named coenzyme F -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 F H . Our results provide structural insights into this unique fusion, in which a primitive sulfite reductase turns a poison into an elementary block of life.

• Subject: Euryarchaeota / Methanococcales - metabolism / Oxidation-Reduction / Oxidoreductases Acting on Sulfur Group Donors / Riboflavin - chemistry / Riboflavin - metabolism / Sulfites