Fas and Fas Ligand （FasL） are members of the TNF superfamily and are type I and type II transmembrane proteins， respectively. Binding of FasL to Fas initiates apoptosis in Fas-bearing cells. The apoptosis mechanism involves the recruitment of pro-caspase 8 through an adaptor molecule named FADD followed by processing of the pro-enzyme to active forms. These active caspases subsequently cleave a variety of cellular substrates leading to the eventual cell death. sFasR is able to inhibit FasL-induced apoptosis by acting as a decoy receptor whicht serves as a sink for FasL. The full length Fas Receptor is a 319 a.a type I transmembrane protein， which contains a 157 a.a extracellular domain， a 17 a.a transmembrane domain， and 145 a.a cytoplasmic domain. The mature human Fas ECD shares 55%， 58%， a.a sequence identity with the mouse， rat， Fas， respectively.
