title: Binding of the Drosophila cytokine Spätzle to Toll is direct and establishes signaling.
abstract: The extracellular protein Spätzle is required for activation of the Toll signaling pathway in the embryonic development and innate immune defense of Drosophila. Spätzle is synthesized as a pro-protein and is processed to a functional form by a serine protease. We show here that the mature form of Spätzle triggers a Toll-dependent immune response after injection into the hemolymph of flies. Spätzle specifically bound to Drosophila cells and to Cos-7 cells expressing Toll. Furthermore, in vitro experiments showed that the mature form of Spätzle bound to the Toll ectodomain with high affinity and with a stoichiometry of one Spätzle dimer to two receptors. The Spätzle pro-protein was inactive in all these assays, indicating that the pro-domain sequence, which is natively unstructured, acts to prevent interaction of the cytokine and its receptor Toll. These results show that, in contrast to the human Toll-like receptors, Drosophila Toll requires only an endogenous protein ligand for activation and signaling.
authors.affiliation: Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, United Kingdom.
authors.forename: Alexander N R
authors.initials: AN
authors.lastname: Weber
authors.forename: Servane
authors.initials: S
authors.lastname: Tauszig-Delamasure
authors.forename: Jules A
authors.initials: JA
authors.lastname: Hoffmann
authors.forename: Eric
authors.initials: E
authors.lastname: Lelièvre
authors.forename: Hugues
authors.initials: H
authors.lastname: Gascan
authors.forename: Keith P
authors.initials: KP
authors.lastname: Ray
authors.forename: Mary A
authors.initials: MA
authors.lastname: Morse
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Imler
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Gay
mesh_terms: D000818:Animals; D004330:Drosophila / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D029721:Drosophila Proteins / Q000737:chemistry / Q000378:metabolism*; D019476:Insect Proteins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D051193:Toll-Like Receptors
chemical_list: D029721:Drosophila Proteins; D019476:Insect Proteins; D011956:Receptors, Cell Surface; C068721:Tl protein, Drosophila; D051193:Toll-Like Receptors; C086179:spz protein, Drosophila