WAP

Four-disulfide core domains
WAP
SMART accession number:SM00217
Description:
Interpro abstract (IPR008197):

Peptide proteinase inhibitors can be found as single domain proteins or as single or multiple domains within proteins; these are referred to as either simple or compound inhibitors, respectively. In many cases they are synthesised as part of a larger precursor protein, either as a prepropeptide or as an N-terminal domain associated with an inactive peptidase or zymogen. This domain prevents access of the substrate to the active site. Removal of the N-terminal inhibitor domain either by interaction with a second peptidase or by autocatalytic cleavage activates the zymogen. Other inhibitors interact direct with proteinases using a simple noncovalent lock and key mechanism; while yet others use a conformational change-based trapping mechanism that depends on their structural and thermodynamic properties.

Whey acidic protein (WAP) is a major component of the whey fraction of milk, which contains a significant number of different proteins. WAP proteins share limited sequence identity, except for their conserved cysteine-rich regions, known as 4-disulphide core (4-DSC) domains, and the positional conservation of specific residues [(PUBMED:12751894)]. Several non-milk proteins also contain 4-DSC patterns, such as certain serine protease inhibitors. WAP itself appears to have a protease-inhibitor function, as seen with its inhibitory effect on the progression of cancer cells [(PUBMED:17215074)].

GO component:extracellular region (GO:0005576)
GO function:peptidase inhibitor activity (GO:0030414)
Family alignment:
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There are 1128 WAP domains in 774 proteins in SMART's nrdb database.

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