NGFFFamide and echinotocin: structurally unrelated myoactive neuropeptides derived from neurophysin-containing precursors in sea urchins.
2009
SUMMARY The myoactive neuropeptide NGIWYamide was originally isolated from the
holothurian (sea cucumber) Apostichopus japonicus but there is
evidence that NGIWYamide-like peptides also occur in other echinoderms. Here
we report the discovery of a gene in the sea urchin Strongylocentrotus
purpuratus that encodes two copies of an NGIWYamide-like peptide:
Asn-Gly-Phe-Phe-Phe-(NH 2 ) or NGFFFamide. Interestingly, the
C-terminal region of the NGFFFamide precursor shares sequence similarity with
neurophysins, carrier proteins hitherto uniquely associated with precursors of
vasopressin/oxytocin-like neuropeptides. Thus, the NGFFFamide precursor is the
first neurophysin-containing neuropeptide precursor to be discovered that does
not contain a vasopressin/oxytocin-like peptide. However, it remains to be
determined whether neurophysin acts as a carrier protein for NGFFFamide. The
S. purpuratus genome also contains a gene encoding a precursor
comprising a neurophysin polypeptide and `echinotocin9 (CFISNCPKGamide)–
the first vasopressin/oxytocin-like peptide to be identified in an
echinoderm. Therefore, in S. purpuratus there are two genes encoding
precursors that have a neurophysin domain but which encode neuropeptides that
are structurally unrelated. Furthermore, both NGFFFamide and echinotocin cause
contraction of tube foot and oesophagus preparations from the sea urchin
Echinus esculentus , consistent with the myoactivity of NGIWYamide in
sea cucumbers and the myoactivity of vasopressin/oxytocin-like peptides in
other animal phyla. Presumably the NGFFFamide precursor acquired its
neurophysin domain following partial or complete duplication of a gene
encoding a vasopressin/oxytocin-like peptide, but it remains to be determined
when in evolutionary history this occurred.
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