Fas/FasL

Fas (CD95, APO-1) belongs to the death receptor family, a subgroup of the tumor necrosis factor/nerve growth factor (TNF/NGF) receptor superfamily. These cell surface cytokine receptors are able to initiate an apoptotic signaling cascade after binding a group of structurally related ligands or specific antibodies [1]. The members of this family are type-I transmembrane proteins with a C-terminal intracellular tail, a membrane spanning region, and an extracellular N-terminal domain. Through interaction with the N-terminal domain, the receptors bind their cognate ligands (called death ligands), the majority of which are type-II transmembrane proteins belonging to the TNF family of proteins and comprised of an intracellular N-terminal domain, a transmembrane region, and a C-terminal extracellular tail. The signature features of the death receptors are represented by a highly homologous region in their extracellular domains containing one to five cysteine-rich domains (CRD) and a ∼80-amino acid cytoplasmic sequence known as death domain (DD), which is required to initiate the death signal.