Molecular Biology Of The Cell 6th Edition by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter

Exercise 7

Discuss the following problems.
-Fas ligand is a trimeric, extracellular protein that binds to its receptor, Fas, which is composed of three iden- tical transmembrane subunits (Figure Q18-3). The bind- ing of Fas ligand alters the conformation of Fas so that it binds an adaptor protein, which then recruits and acti- vates caspase-8, triggering a caspase cascade that leads to cell death. In humans, the autoimmune lymphoprolifera- tive syndrome (ALPS) is associated with dominant muta- tions in Fas that include point mutations and C-terminal truncations. In individuals that are heterozygous for such mutations, lymphocytes do not die at their normal rate and accumulate in abnormally large numbers, causing a vari- ety of clinical problems. In contrast to these patients, indi- viduals that are heterozygous for mutations that eliminate Fas expression entirely have no clinical symptoms.