Mapping of the linear site on the Fas/APO-1 molecule targeted by the prototypic anti-Fas mAb

: Fas/APO-1 is a member of the nerve growth factor/tumor necrosis factor (TNF) family of receptors and has been shown to mediate apoptotic cell death upon binding of specific mAb. We report here that the prototypic anti-human Fas mAb (clone CH-11) induces apoptosis by binding to a linear epitope present on the extracellular domain of the Fas/APO-1 protein. Synthetic peptides corresponding to this epitope blocked the apoptotic effect of the antibody in a susceptible Jurkat T cell line. Based upon the similarity between the Fas/APO-1 protein and the recently crystallized soluble TNF receptor type I, we generated a molecular model of Fas/APO-1, Our computer modeling indicates that the antibody binding region forms a hairpin loop on the surface of the Fas/ APO-1 protein. These findings further our understanding of the Fas/APO-1-mediated apoptotic signal and may provide a useful tool in future investigations of programmed cell death.