Guanylin is a 15

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

peptide that is secreted by

goblet cells Goblet cells are simple columnar epithelial cells that secrete gel-forming mucins, like mucin 5AC. The goblet cells mainly use the merocrine method of secretion, secreting vesicles into a duct, but may use apocrine methods, budding off their secr ...

in the colon. Guanylin acts as an agonist of the

guanylyl cyclase Guanylate cyclase (EC 4.6.1.2, also known as guanyl cyclase, guanylyl cyclase, or GC; systematic name GTP diphosphate-lyase (cyclizing; 3′,5′-cyclic-GMP-forming)) is a lyase enzyme that converts guanosine triphosphate (GTP) to cyclic guanos ...

receptor GC-C and regulates electrolyte and

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

transport in

intestinal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans an ...

and

renal The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; bloo ...

epithelia Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellular ...

. Upon receptor binding, guanylin increases the intracellular concentration of

cGMP CGMP is an initialism. It can refer to: *cyclic guanosine monophosphate (cGMP) *current good manufacturing practice (cGMP) *CGMP, Cisco Group Management Protocol, the Cisco version of Internet Group Management Protocol The Internet Group Managem ...

, induces chloride secretion and decreases intestinal fluid absorption, ultimately causing

diarrhoea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...

. The peptide stimulates the enzyme through the same receptor binding region as the

heat-stable enterotoxin Heat-stable enterotoxins (STs) are secretory peptides produced by some bacterial strains, such as enterotoxigenic ''Escherichia coli'' which are in general toxic to animals. These peptides keep their 3D structure and remain active at temperatu ...

s. Researches have found that a loss in guanylin expression can lead to colorectal cancer due to guanylyl cyclase C's function as an intestinal tumor suppressor. When guanylin expression was measured on over 250 colon cancer patients, more than 85% of patients had a loss of guanylin expression in cancerous tissue samples by 100-1000 times when compared to the same patients's nearby healthy colon tissue. Another study done on genetically engineered mice found that mice on a high calorie diet had reduced guanylin expression in the colon. This loss of expression then resulted in guanylyl cyclase C inhibition and the formation of tumors, therefore linking diet-induced obesity with colorectal cancer.

Human proteins containing this domain

GUCA2A; GUCA2B;

Structure

This peptide has two topogies, both isoforms are shown below:

References

External links

* Peptides Protein domains {{biochem-stub