Identification of evolutionarily conserved residues required for the bioactivity of a pedal peptide/orcokinin-type neuropeptide.

Starfish myorelaxant peptide (SMP) belongs to a bilaterian family of pedal peptide/orcokinin (PP/OK)-type neuropeptides that have evolutionarily conserved structural features. Here we report the first analysis of the structure-activity relationships of SMP and identify key residues for SMP bioactivity, including hydrophobic residues located in the N- and C-terminal regions that are conserved in PP/OK-type peptides in other phyla as well as core residues that are only conserved in echinoderm PP/OK-type peptides.