A leucine‐rich repeat peptide derived from the Drosophila Toll receptor forms extended filaments with a β‐sheet structure

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Abstract
Leucine‐rich repeats (LRRs) are 22–28 amino acid‐long sequence motifs found in a family of cytoplasmic, membrane and extracellular proteins. There is evidence that LRRs function in signal transduction, cellular adhesion and protein‐protein interactions. Here we report unusual properties of a synthetic LRR peptide derived from the sequence of the Drosophila membrane receptor Toll. In neutral solution the peptide forms a gel revealed by electron microscopy to consist of extended filaments approximately 8 nm in thickness. As the gel forms, the circular dichroism spectrum of the peptide solution changes from one characteristic of random coil to one associated with β‐sheet structures. Molecular modelling suggests that the peptides form an amphipathic structure with a predominantly apolar and charged surface. Based on these results, models for the gross structure of the peptide filaments and a possible molecular mechanism for cellular adhesion are proposed.