Neuropeptide precursors in Tribolium castaneum

Abstract

Neuropeptides and neurohormones are among the more diverse and functionally important classes of cell-to-cell signaling molecules involved in animal development and behavior. Less is known about the hormones and neuropeptides of the red flour beetle, Tribolium castaneum, than many other insects. However, the genomic information becoming available from this organism presents an opportunity to identify multiple neuropeptide and hormone genes, and hence their associated protein precursors. Using similarity-based prediction, we report new neuropeptides and hormone precursors from T. castaneum, bringing the number of annotated precursors to 37. We identified one prohormone (SVDPIDGDLIG-containing) having little similarity to other insect prohormones. The conversion of the protein precursors into bioactive peptides requires a suite of processing enzymes and a number of enzymatic steps; using the web-based NeuroPred application and similarity-based bioinformatics approaches, we predict 132 likely peptides that may result from the enzymatic processing of these gene products.

Figure 1

Comparison of prohormone organization and sequences for the red swamp crayfish, Procambarus clarkii orcokinin (7619888_7619889), the honey bee, A. mellifera, orcokinin and SVDPIDGDLIamide–containing precursors (this study). Signal peptide is indicated with dashed line, and solid underline indicates peptides predicted using a cleavage prediction model trained on Apis and Drosophila precursors. Double underline indicates peptides confirmed by MS analysis. Orcokinin contains 13 highly similar peptides and two additional peptides. The repetitive occurrence of short peptides is also displayed in the SVDPIDGDLIG-containing prohormone. In contrast, the orcokinin-related Apis prohormone contains five peptides, of which two show considerable sequence similarity.