title: Functional insights from the crystal structure of the N-terminal domain of the prototypical toll receptor.
abstract: Drosophila melanogaster Toll is the founding member of an important family of pathogen-recognition receptors in humans, the Toll-like receptor (TLR) family. In contrast, the prototypical receptor is a cytokine-like receptor for Spätzle (Spz) protein and plays a dual role in both development and immunity. Here, we present the crystal structure of the N-terminal domain of the receptor that encompasses the first 201 amino acids at 2.4 Å resolution. To our knowledge, the cysteine-rich cap adopts a novel fold unique to Toll-1 orthologs in insects and that is not critical for ligand binding. However, we observed that an antibody directed against the first ten LRRs blocks Spz signaling in a Drosophila cell-based assay. Supplemented by point mutagenesis and deletion analysis, our data suggests that the region up to LRR 14 is involved in Spz binding. Comparison with mammalian TLRs reconciles previous contradictory findings about the mechanism of Toll activation.
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge, CB2 1GA, UK. Electronic address: mg308@cam.ac.uk.
authors.forename: Monique
authors.initials: M
authors.lastname: Gangloff
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge, CB2 1GA, UK.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Arnot
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge, CB2 1GA, UK.
authors.forename: Miranda
authors.initials: M
authors.lastname: Lewis
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge, CB2 1GA, UK. Electronic address: njg11@cam.ac.uk.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Gay
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002460:Cell Line; D018360:Crystallography, X-Ray; D029721:Drosophila Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D004331:Drosophila melanogaster / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D051193:Toll-Like Receptors / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000906:Antibodies; D029721:Drosophila Proteins; D011993:Recombinant Fusion Proteins; C068721:Tl protein, Drosophila; D051193:Toll-Like Receptors; C086179:spz protein, Drosophila