Development of potent biocatalysts for enzymatic detoxification of estrogenic mycotoxin zearalenone (ZEN) and its more toxic derivative alpha-zearalenol (alpha-ZOL) is of great interest. Here, we report the crystal structures of a ZEN-hydrolyzing enzyme from Rhinocladiella mackenziei (RmZHD), including substrate complexes. A molecular mechanism for the distinct activity of RmZHD in hydrolyzing the structurally similar ZEN and alpha-ZOL is then proposed. In addition, structure-based engineering to modify the substrate-binding pocket and improve the RmZHD activity toward alpha-ZOL is presented. These results expand our scope in understanding the catalytic mechanism of ZHD-family enzymes and are of vital importance in further industrial applications.
Title: Chasing the elusive Euryarchaeota class WSA2: genomes reveal a uniquely fastidious methyl-reducing methanogen Nobu MK, Narihiro T, Kuroda K, Mei R, Liu WT Ref: Isme J, 10:2478, 2016 : PubMed
The ecophysiology of one candidate methanogen class WSA2 (or Arc I) remains largely uncharacterized, despite the long history of research on Euryarchaeota methanogenesis. To expand our understanding of methanogen diversity and evolution, we metagenomically recover eight draft genomes for four WSA2 populations. Taxonomic analyses indicate that WSA2 is a distinct class from other Euryarchaeota. None of genomes harbor pathways for CO2-reducing and aceticlastic methanogenesis, but all possess H2 and CO oxidation and energy conservation through H2-oxidizing electron confurcation and internal H2 cycling. As the only discernible methanogenic outlet, they consistently encode a methylated thiol coenzyme M methyltransferase. Although incomplete, all draft genomes point to the proposition that WSA2 is the first discovered methanogen restricted to methanogenesis through methylated thiol reduction. In addition, the genomes lack pathways for carbon fixation, nitrogen fixation and biosynthesis of many amino acids. Acetate, malonate and propionate may serve as carbon sources. Using methylated thiol reduction, WSA2 may not only bridge the carbon and sulfur cycles in eutrophic methanogenic environments, but also potentially compete with CO2-reducing methanogens and even sulfate reducers. These findings reveal a remarkably unique methanogen 'Candidatus Methanofastidiosum methylthiophilus' as the first insight into the sixth class of methanogens 'Candidatus Methanofastidiosa'.
