Fas Death Domain
Fas is a cytokine receptor which mediates programmed cell death, or apoptosis. This is imperative for the removal of autoreactive T cells in order to maintain the homeostasis of the immune-system. The self-association of a conserved cytoplasmic region of Fas known as the death domain is what actually signals cell death. This domain then interacts with another death-domain-containing protein, FADD.
The Fas death domain is 127 amino acid residues long. Its structure consists of 6 antiparallel, amphipathic alpha-helices (purple).