High level expression of the Drosophila Toll receptor ectodomain and crystallization of its complex with the morphogen Spätzle.

Drosophila Toll receptors are involved in embryonic development and in the immune response of adult flies. In both processes, the Toll receptor ligand is the NGF-like cystine knot protein Spätzle. Here we present the expression of Toll receptor ectodomain in Schneider cells at high yields and demonstrate a high affinity interaction with the refolded and trypsin-processed Spätzle cystine knot domain dimer. Poorly and anisotropically diffracting crystals of the complex could be improved by deglycosylation and dehydration, paving the way for structural analyses of the Toll-Spätzle interaction.