Molecular insights into the formation of the DNA-degradosome complex
The human apoptosis induced factor, AIF, is released from the mitochondrial intermembrane space to the cytosol when receiving an apoptotic insult. Once in the cytosol, interaction with cyclophilin A (CypA) is proposed to favor the optimal nuclear translocation of both proteins. In the nucleus, the AIF:CypA complex is envisaged to recruit the histone H2AX to produce a ternary complex known as “degradosome”. This ternary complex would bind DNA, inducing chromatin condensation and cell disassembly in a caspase-independent manner. We have used different methods to prove the ability of apoptotic AIF isoform, AIFΔ101, to in vitro simultaneously assemble CypA and H2AX, including the energetically optimized simulation of ensembles for the degradosome. The constructed models agree well with single molecule topologies as well as with determined binding parameters, all of them demonstrating flexibility at the interplay surfaces within proteins. In addition, binding studies show that all DNA-degradosome components are able to produce binary interactions and to bind to the rest of partners, envisaging binding cooperativity. Altogether these data evidence for the first time at the molecular level the AIFΔ101 simultaneous interplay with all components of the DNA-degradosome complex and point to some features that might contribute to its assembly in a cellular context.