Crustacean Cardioactive Peptide

= History and structure =

CCAP is a highly conserved, amidated cyclic nonapeptide with the primary structure PFCNAFTGC-NH₂ (ProPheCysAsnAlaPheTyrGlyCys-NH₂) and a disulfide bridge between Cys3 and Cys9. It is found in crustaceans and insects where it behaves as a cardioaccelerator, neuropeptide transmitter for other areas of the nervous system and a hormone. CCAP was first isolated from the pericardial organs of the shore crab "Carcinus maenas", where it has a role in regulating heartbeat. It was assumed that this was the peptide’s main function and its name reflects this.

Function

As well as "C. maenas", CCAP has cardioacceleratory properties in "Manduca sexta" and "Drosophila melanogaster" [Nichols et al., 1999] ; it is a highly conserved protein found in species as diverse as moths and fruit flies in addition to the crustacean it was originally identified in. Interestingly, under specific conditions, CCAP has also been shown to induce cardiac reversal in "M. sexta" and "D. melanogaster" [Dulcis et al., 2001, Dulcis et al., 2005 and Dulcis and Levine, 2004] and cardiac inhibition in "Locusta migratoria".Fact|date=February 2008

Since CCAP was first identified and its possible role suggested, it has been proven it serves many other functions. It regulates release of adipokinetic hormone during sustained flight in "L. migratoria". It is also important in metabolism and digestion in other species; CCAP is involved as a hormone in the cockroach "Periplaneta americana" [Stangier et al., 1989, Donini et al., 2002 and Lange and Patel, 2005] by upregulating digestive hormones after the insect has fed on nutritional matter. In the crab "Cancer borealis" CCAP controls passage of food through the forgut by modulating the stomatogastric ganglion’s pyloric rhythm [Heinzel et al., 1997] . This suggests CCAP is involved primarily in movement of food along the gut, facilitating digestion by secretion of digestive hormones and increasing flow of blood.

The effects of CCAP on the reproductive organs of females of the species "L. migratoria" have also been studied. The peptide stimulates the contraction of the oviducts and spermatheca [de Silva and Lange, 2006] . There is no CCAP or CCAP-like immunoreactivity shown in the oviduct or the nerves innervating the oviduct so it is probable that CCAP acts as a neurohormone to perform these functions.

CCAP is one of several peptides and hormones to be involved in the moulting process of crustaceans [Cheung et al., 1999] and insects.

Effects of lack of CCAP

There have been no mutant individuals of any species found to possess CCAP who have a genetic defect meaning they are not able to produce the peptide. It is likely any such mutation would be lethal. In "Drosophila" the destruction of CCAP-containing neurons during development causes major changes in and disruptions to timing and behaviour of moulting [Park et al., 2003] .

References and further reading