Recombinant Feline Fas/TNFRSF6/CD95 Fc Chimera Protein, CF

Feline Fas (fibroblast associated; also named CD95 and APO-1) is a 45 kDa type I transmembrane (TM) glycoprotein that is a member of the TNF receptor superfamily (1 - 3). The family contains about 30 members, and is characterized by the presence of at least one cysteine-rich domain that contains multiple intrachain disulfide bonds. In general, the superfamily is divided into cytoplasmic death domain (DD) containing, and non-DD containing receptors (3). Feline Fas is synthesized as a 314 amino acid (aa) precursor that contains a 24 aa signal sequence, a 148 aa extracellular region, a 16 aa TM segment and a 126 aa cytoplasmic tail (4). The extracellular region contains four potential N-linked glycosylation sites plus two distinct cysteine-rich domains of approximately 40 aa each; the cytoplasmic tail shows a 45 aa DD. The extracellular region of feline Fas shares 68%, 65%, 53%, and 58% aa sequence identity to porcine, human, mouse and rat Fas, respectively. There are five alternate splice forms of feline Fas, which vary from 132 aa to 209 aa in length. All utilize exons 1 - 3 (aa 1 - 111) and all are missing the transmembrane segment of the full length form (5). Circulating Fas is reported to be both a dimer and trimer at low ng/mL concentrations. The ligand for Fas is FasL, and Fas ligation activates both the MEK cascade and FADD/caspase-8 pathway (7).