The PA domain: a protease-associated domain

We have identified a similarity between the apical domain of the human tran sferrin receptor and several other protein families. This domain is found a ssociated with two different families of peptidases. Therefore, we term it the PA domain for protease-associated domain. The PA domain is found insert ed within a loop of the peptidase domain of family M8/M33 zinc peptidases. The PA domain is also found in a vacuolar sorting receptor and a ring finge r protein of unknown function that may be a cell surface receptor. The PA d omain may mediate substrate determination of peptidases or form protein-pro tein interactions.