A New Type of Sulfite Reductase, a Novel Coenzyme F420-dependent Enzyme, from the Methanarchaeon Methanocaldococcus jannaschii

Eric F Johnson,Biswarup Mukhopadhyay

doi:10.1074/jbc.m503492200

Abstract

Methanocaldococcus jannaschii is a hypertheromphilic, strictly hydrogenotrophic, methanogenic archaeon of ancient lineage isolated from a deep-sea hydrothermal vent. It requires sulfide for growth. Sulfite is inhibitory to the methanogens. Yet, we observed that M. jannaschii grows and produces methane with sulfite as the sole sulfur source. We found that in this organism sulfite induces a novel, highly active, coenzyme F(420)-dependent sulfite reductase (Fsr) with a cell extract specific activity of 0.57 mumol sulfite reduced min(-1) mg(-1) protein. The cellular level of Fsr protein is comparable to that of methyl-coenzyme M reductase, an enzyme essential for methanogenesis and a possible target for sulfite. Purified Fsr reduces sulfite to sulfide using reduced F(420) (H(2)F(420)) as the electron source (K(m): sulfite, 12 microm; H(2)F(420), 21 microm). Therefore, Fsr provides M. jannaschii an anabolic ability and protection from sulfite toxicity. The N-terminal half of the 70-kDa Fsr polypeptide represents a H(2)F(420) dehydrogenase and the C-terminal half a dissimilatory-type siroheme sulfite reductase, and Fsr catalyzes the corresponding partial reactions. Previously described sulfite reductases use nicotinamides and cytochromes as electron carriers. Therefore, this is the first report of a coenzyme F(420)-dependent sulfite reductase. Fsr homologs were found only in Methanopyrus kandleri and Methanothermobacter thermautotrophicus, two strictly hydrogenotrophic thermophilic methanogens. fsr is the likely ancestor of H(2)F(420) dehydrogenases, which serve as electron input units for membrane-based energy transduction systems of certain late evolving archaea, and dissimilatory sulfite reductases of bacteria and archaea. fsr could also have arisen from lateral gene transfer and gene fusion events.

Highlights

Growth of M. jannaschii with Sulfite as the Sulfur Source and Expression of a Novel Sulfite Reductase—M. jannaschii used sulfite as the sole sulfur source for growth; the growth and methane formation patterns were similar to that seen with a culture grown with the same level of sulfide (Fig. 1)
Sulfide is an essential nutrient for M. jannaschii [8], and sulfite is inhibitory to the methanogens [1]
We found that this methanogenic archaeon was able to use sulfite as a sole sulfur source and did not show a significant inhibition of methanogenesis by this oxyanion (Fig. 1)

Summary

Introduction

This article must be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 To whom correspondence should be addressed: Virginia Bioinformatics Institute, Bioinformatics I, Virginia Polytechnic Institute and State University, 0477 Washington St., Blacksburg, VA 24061. Tolerate and even use sulfite as a sole sulfur source [6, 7]. As shown in this report, Methanocaldococcus jannaschii, a deeply rooted hyperthermophilic methanogenic archaeon isolated from a deep-sea hydrothermal vent [8], grows with sulfite. The genomes of M. thermautotrophicus and M. jannaschii do not carry a clear homolog of a sulfite reductase [9, 10]; the genome sequence of M. thermolithotrophicus is yet to be determined. This work has led to the discovery of a new type of sulfite reductase

Methods

Results

Conclusion