PA _GRAIL_like: Protease-associated (PA) domain GRAIL-like. This group includes PA domain containing E3 (ubiquitin ligases) similar to human GRAIL (gene related to anergy in lymphocytes) protein. Proteins in this group contain a C3H2C3 RING finger. E3 ubiquitin ligase is part of an enzymic cascade, the end result of which is the ubiquitination of proteins. In this cascade, E1 activates the ubiquitin, the activated ubiquitin is carried by E2, and E3 recognizes the acceptor protein as well as catalyzes the transfer of the activated ubiquitin from E2 to this acceptor. GRAIL, a transmembrane protein localized in the endosomes, controls the development of T cell clonal anergy, and may ubiquitinate membrane-associated targets for T cell activation. GRAIL1 is associated with, and regulated by, two isoforms of otubain 1 (the ubiquitin-specific protease). Additional E3s belonging to this group include human (h)Goliath and Xenopus GREUL1 (Goliath Related E3 Ubiquitin Ligase 1). hGoliath and GRAIL both have the property of self-ubiquitination. hGoliath is expressed in leukocytes; its expression and localization is not modified in leukemia. GREUL1 may play a role in the generation of anterior ectoderm. The significance of the PA domain to these proteins has not been ascertained. It may be a protein-protein interaction domain. At peptidase active sites, the PA domain may participate in substrate binding and/or promoting conformational changes, which influence the stability and accessibility of the site to substrate.
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