title: Role of the Spatzle Pro-domain in the generation of an active toll receptor ligand.
abstract: The cytokine Spätzle is the ligand for Drosophila Toll, the prototype of an important family of membrane receptors that function in embryonic patterning and innate immunity. A dimeric precursor of Spätzle is processed by an endoprotease to produce a form (C-106) that cross-links Toll receptor ectodomains and establishes signaling. Here we show that before processing the pro-domain of Spätzle is required for correct biosynthesis and secretion. We mapped two loss-of-function mutations of Spätzle to a discrete site in the pro-domain and showed that the phenotype arises because of a defect in biosynthesis rather than signaling. We also report that the pro-domain and C-106 remain associated after cleavage and that this processed complex signals with the same characteristics as the C-terminal fragment. These results suggest that before activation the determinants on C-106 that bind specifically to Toll are sequestered by the pro-domain and that proteolytic processing causes conformational rearrangements that expose these determinants and enables binding to Toll. Furthermore, we show that the pro-domain is released when the Toll extracellular domain binds to the complex, a finding that has implications for the generation of a signaling-competent Toll dimer.
authors.affiliation: Department of Biochemistry, Cambridge University, 80 Tennis Court Road, Cambridge CB2 1GA, United Kingdom. alexander.weber@dkfz-heidelberg.de
authors.forename: Alexander N R
authors.initials: AN
authors.lastname: Weber
authors.forename: Monique
authors.initials: M
authors.lastname: Gangloff
authors.forename: Martin C
authors.initials: MC
authors.lastname: Moncrieffe
authors.forename: Yann
authors.initials: Y
authors.lastname: Hyvert
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Imler
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Gay
mesh_terms: D000818:Animals; D016207:Cytokines / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D029721:Drosophila Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster; D008024:Ligands; D011485:Protein Binding / Q000502:physiology; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology; D051193:Toll-Like Receptors / Q000378:metabolism*
chemical_list: D016207:Cytokines; D029721:Drosophila Proteins; D008024:Ligands; D051193:Toll-Like Receptors; C086179:spz protein, Drosophila