A ligand whose proteolytically activated form stimulates the Toll receptor in Drosophila melanogaster.
Proteolytic processing makes the receptor-active ligand available at the appropriate place and time. This separates production of a precursor from creation of an active extracellular signal, allowing localization of a developmental response. [ref]
Molecular Biology of the Cell, 4th edition by Bruce Alberts and others. Chapter 21, Early Animal Development: dorsal-ventral patterning
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