Structural And Functional Study Of CED-4Apoptosome Of Caenorhabditis Elegans

Apoptosis plays an important role in metazoan development and tissuehomeostasis. The occurrence of apoptosis is controlled meticulously by aconserved biochemical pathway. Neuro-degenerative diseases like Alzheimer'sdisease will occur when apoptosis is excessive, on the other hand, cancer willemerge when apoptosis is insufficient.Formation of apoptosome, which is required for the activation of proteasesinvolved in apoptosis, is a central event in apoptosis.C. elegans is an important model organism that we commenced to studyapoptosis. The apoptosis of C. elegans is controlled by a linear pathway whichconsists of EGL-1, CED-9, CED-4and CED-3. CED-4apoptosome is themolecular machine which is required for the activation of CED-3caspase andinitiation of apoptosis.At present, it is still unknown about how CED-4apotosome activatesCED-3. Therefore, we want to elucidate this question through structural andfunctional study into CED-4via crystallographic and biochemical methods.Finally, we determined the crystal structure of CED-4octomer, which isthe first high resolution structure of apoptosome. CED-4apoptosome consists ofeight CED-4molecules,which is organized as a tetramer of dimmers. As amember of the AAA+ATPase family, CED-4molecules in apoptosome interactwith adjacent molecules via unreported interface, which is different with that ofother members' structure. Meanwhile, because CED-4is an important memberof NB-ARC family, the study of structure and function of CED-4apoptosomemay impact on the understanding of the other members of NB-ARC family.We also purified CED-4/CED-3complex. Surprisingly, CED-4apoptosomebinds only two CED-3molecules, not eight molecules proposed in formermodels. According to the biochemical data, we proposed the holoenzyme model:CED-4apoptosome recruits two CED-3molecules, promotes the dimerization ofCED-3and enhances the activity of CED-3, which leads to the apoptosis ultimately.