title: Evolutionary and functional epitopes of the Spätzle protein: new insights into activation of the Toll receptor.
abstract: Spätzle, a dimeric ligand, binds to the Drosophila Toll receptor and activates the signal pathway functioning in both embryonic patterning and innate immunity. Here, we used the evolutionary trace approach based on phylogenetic information to predict the evolutionary epitope of Spätzle and found that it mainly clusters in several adjacent loops of Spätzle far from the cystine-knot structural domain. We designed six mutants of Spätzle based on the evolutionary epitope and transfected them into a stable cell line expressing the luciferase reporter gene under the control of the drosomycin promoter. Luciferase assays showed that these mutants cannot significantly activate the drosomycin promoter, suggesting the involvement of these sites in binding of Spätzle to the Toll receptor. These data highlight the importance of the Trp-loop of the mushroom-shaped Spätzle dimer in Toll receptor activation and demonstrate that evolution-guided site-specific mutagenesis represents a useful and promising strategy for understanding the ligand-receptor interaction.
authors.affiliation: Group of Animal Innate Immunity, State Key Laboratory of Integrated Management of Pest Insects & Rodents, Institute of Zoology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: S
authors.initials: S
authors.lastname: Zhu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019521:Body Patterning; D019295:Computational Biology; D019281:Dimerization; D004330:Drosophila / Q000378:metabolism*; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D017930:Genes, Reporter; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D051193:Toll-Like Receptors / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; C068721:Tl protein, Drosophila; D051193:Toll-Like Receptors; C086179:spz protein, Drosophila; C091227:DRS protein, Drosophila