title: The Oxidosqualene Cyclase from the OomyceteSaprolegnia parasiticaSynthesizes Lanosterol as a Single Product.
abstract: The first committed step of sterol biosynthesis is the cyclisation of 2,3-oxidosqualene to form either lanosterol (LA) or cycloartenol (CA). This is catalyzed by an oxidosqualene cyclase (OSC). LA and CA are subsequently converted into various sterols by a series of enzyme reactions. The specificity of the OSC therefore determines the final composition of the end sterols of an organism. Despite the functional importance of OSCs, the determinants of their specificity are not well understood. In sterol-synthesizing oomycetes, recent bioinformatics, and metabolite analysis suggest that LA is produced. However, this catalytic activity has never been experimentally demonstrated. Here, we show that the OSC of the oomyceteSaprolegnia parasitica, a severe pathogen of salmonid fish, has an uncommon sequence in a conserved motif important for specificity. We present phylogenetic analysis revealing that this sequence is common to sterol-synthesizing oomycetes, as well as some plants, and hypothesize as to the evolutionary origin of some microbial sequences. We also demonstrate for the first time that a recombinant form of the OSC fromS. parasiticaproduces LA exclusively. Our data pave the way for a detailed structural characterization of the protein and the possible development of specific inhibitors of oomycete OSCs for disease control in aquaculture.
authors.affiliation: Division of Glycoscience, School of Biotechnology, KTH Royal Institute of TechnologyStockholm, Sweden; Department of Ecology, Environment and Plant Sciences, Stockholm UniversityStockholm, Sweden.
authors.forename: Paul
authors.initials: P
authors.lastname: Dahlin
authors.affiliation: Division of Glycoscience, School of Biotechnology, KTH Royal Institute of Technology Stockholm, Sweden.
authors.forename: Vaibhav
authors.initials: V
authors.lastname: Srivastava
authors.affiliation: Division of Glycoscience, School of Biotechnology, KTH Royal Institute of TechnologyStockholm, Sweden; ARC Centre of Excellence in Plant Cell Walls, School of Agriculture, Food and Wine, The University of Adelaide, UrrbraeSA, Australia.
authors.forename: Vincent
authors.initials: V
authors.lastname: Bulone
authors.affiliation: Division of Glycoscience, School of Biotechnology, KTH Royal Institute of TechnologyStockholm, Sweden; Wallenberg Wood Science Centre, KTH Royal Institute of TechnologyStockholm, Sweden.
authors.forename: Lauren S
authors.initials: LS
authors.lastname: McKee
keywords: Saprolegnia parasitica; lanosterol biosynthesis; oomycete; oxidosqualene cyclase; sterols