There is no MUC18 in this series because it is a well published alias for the unrelated gene MCAM Mucins are a family of high molecular weight, heavily glycosylated proteins ( glycoconjugates ) produced by epithelial tissues in most metazoans. Mucins'' key characteristic is their ability to form gels; therefore they are a key component in most gel-like secretions, serving functions from lubrication to cell signalling to forming chemical barriers. They often take an inhibitory role. Some mucins are associated with controlling mineralization, including nacre formation in mollusks, calcification in echinoderms and bone formation in vertebrates. They bind to pathogens as part of the immune system. Overexpression of the mucin proteins, especially MUC1, is associated with many types of cancer.
Although some mucins are membrane -bound due to the presence of a hydrophobic membrane-spanning domain that favors retention in the plasma membrane, most mucins are secreted onto mucosal surfaces or secreted to become a component of saliva.