RELATIONSHIPS AMONG THE FMRFAMIDE-LIKE PEPTIDES

More than a hundred FMRFamide-related peptides (FARPs) from most of the major phyla have been identified by their binding to FMRFamide antisera, by their actions on FMRFamide bioassays, or by their occurrence in FMRFamide precursors. This chapter describes the relationships among the FMRFamide-like peptides and examines the three ways of examining these relationships––that is, according to the specific similarities of structure, bioactivity, and genetic affinity that can yield quite different pictures of the family. The nuclear family of FaRPs appears to be restricted to the protostome invertebrate phyla: Mollusca, Arthropoda, Annelida, and Nematoda. Neither the origin nor the range of the family has been definitively established–– that is, no genuine homologs have been demonstrated yet in the flatworms, and neither the pseudocoelomate phyla related to the nematodes, nor the coelomate relatives of the annelids have been examined. The ubiquity of the convergent FARPs can reflect a conserved family of complementary heptahelical receptors requiring the arginyl residue for binding; however, another selective advantage can be the protection provided by a penultimate Arg against certain deamidating peptidases, found so far in yeast and mammals. © 1992, Academic Press Inc.