Whey Acidic Protein (WAP)

Whey Acidic Protein (WAP) is the major milk protein in certain mammals. It has been found in two monotremes, three marsupials, rodents, rabbits, pigs and camel. Despite extensive studies it has not been found in ruminants and humans.

Whey Acidic Protein contains two to three four-disulfide core domain, also termed WAP domain or WAP motif. Each disulfide bond of the WAP motif is made up of two cysteine molecule. This motif is also found in other proteins of different functions, which led to the suggestion that WAP is associated with antiprotease or antibacterial properties. It has been found that humans and ruminants have the WAP gene in their genome as pseudogene. Although humans and ruminants do not seem to encode the gene, there is no detrimental effect. However, mouse pups feeding on maternal milk lacking Whey Acidic Protein has been associated with poor growth rate and lethality.