The death domain (DD) superfamily of proteins share one or more of the following domains: the DD, DED (death-effector domain), CARD (caspase-recruitment domain) and PYD (Pyrin domain). Each of these domains is characterized by a canonical death domain fold, which consists of a bundle of five or six antiparallel α-helices. As their names suggest, these domains play prominent roles in programmed cell death. Caspase-associated recruitment domains (CARDs) mediate the interaction between adaptor proteins such as Apaf-1 and the proform of caspases (e.g., CASP9) participating in apoptosis. ASC (apoptosis-associated speck-like protein containing a CARD, also known as TMS1or PYCARD) is a member of the CARD-containing adaptor protein family. ASC is a 195 amino acid protein, containing a N-terminal Pyrin-like domain (PYD) and an 87 residue C-terminal CARD. This motif is characteristic of numerous proteins involved in apoptotic signaling. ASC2 (apoptosis-associated speck-like protein containing a CARD 2), also known as Pyrin-only protein 1 or PADD-only protein 1, is an 89 amino acid member of the DD superfamily that contains one Pyrin domain. Localized to the cytoplasm, ASC2 interacts with ASC to modulate NF-κB and pro-caspase-1 regulation.
