Eledoisin is an

undecapeptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A ...

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

origin, belonging to the tachykinin family of

neuropeptides Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the ...

. It was first isolated from the posterior

salivary gland The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands ( parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivary ...

s of two mollusk species ''

Eledone ''Eledone'' is a genus of octopuses forming the only genus in the family Eledonidae. It is mainly distributed in the northern and southern Atlantic Ocean, with one species, '' E. palari'', described from the southwestern Pacific Ocean and easter ...

muschata'' and ''Eledone aldovandi'', which belong to the

octopod An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttl ...

order of

Cephalopoda A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent hea ...

.De Marco, A., and G. Gatti, "1H- and 13C-NMR spectra of eledoisin and intermediate oligopeptides." ''Int. J. Pep. Pro. Res.'' 7:437–444, 1975. Other tachykinins from nonmammalian sources include kassinin and physalaemin. The mammalian tachykinins

substance P Substance P (SP) is an undecapeptide (a peptide composed of a chain of 11 amino acid residues) and a member of the tachykinin neuropeptide family. It is a neuropeptide, acting as a neurotransmitter and as a neuromodulator. Substance P and its clo ...

, NKA, and NKB have similar effects as tachykinins of nonmammals and have been more widely studied and characterized. These peptides exhibit a wide and complex spectrum of pharmacological and physiological activities such as

vasodilation Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. The process is the opposite of vasoconstrictio ...

, hypertension, and stimulation of extravascular smooth muscle.R. Christy Rani Grace, Indu R. Chandrashekar and Sudha M. Cowsik
"Solution Structure of the Tachykinin Peptide Eledoisin"
, ''Biophysical Journal'' 84:655-664 (2003), retrieved 05 Dec 2007. This publication has excellent general information on the eledoisin molecule. Eledoisin has the

amino acid sequence Protein primary structure is the linear sequence of amino acids in a peptide or protein. By convention, the primary structure of a protein is reported starting from the amino-terminal (N) end to the carboxyl-terminal (C) end. Protein biosynthe ...

pGlu-Pro-Ser-Lys-Asp-Ala-Phe-Ile-Gly-Leu-Met-NH2 (qPSKDAFIGLM-NH2) where pGlu and q stand for

pyroglutamic acid Pyroglutamic acid (also known as PCA, 5-oxoproline, pidolic acid) is a ubiquitous but little studied natural amino acid derivative in which the free amino group of glutamic acid or glutamine cyclizes to form a lactam. The names of pyroglutamic ac ...

. Like all tachykinin peptides, Eledoisin shares the same consensus C-terminal sequence, that is, Phe-Xxx-Gly-Leu-Met-NH. The invariant "Phe7" residue is probably required for receptor binding. "Xxx" is either an aromatic (phenylalanine, tyrosine) or a branched aliphatic (valine, isoleucine) side chain and is thought to be important in receptor selectivity. This common region, often referred to as the "message domain," is believed to be responsible for activating the receptor. The divergent N-terminal region or the "address domain" varies in amino-acid sequence and length and is believed to play a role in determining the receptor subtype specificity.Schwyzer, R., "Membrane-assisted molecular mechanism of neurokinin receptor subtype selection." ''EMBO J.'' 6:2255–2259, 1987

References

{{Tachykinins Marine neurotoxins Neuropeptides Neurotransmitters Octopus toxins