Chapter 75 – GGNG Peptides

GGNG peptides are a group of excitatory neuropeptides identified from several annelids and a mollusk. Each member of the GGNG peptides is named EEP from the earthworm, LEP from the leech, PEP from the marine worm, and TEP from the marine snail. These peptides consisted of 15–18 amino acids, and have a ring structure made by one disulfide bond. They share the C-terminal GGNG or GGN–NH2 structure. Known bioactivities of GGNG peptides are mostly excitatory; namely, they induce or potentiate the contraction of the digestive tract and sex-associated organs. On the precursor proteins of GGNG peptides so far known, a single copy of the peptide is encoded in the N-terminal or medial region of the protein.