Cytosolic interaction between respiratory cytochrome c and 14-3-3 protein family members facilitates programmed cell death in humans and plants

Resumen

The development, as well as the homeostatic control of multi-cellular organisms, requires programmed cell death processes. In humans and plants, such events entail an intricate protein network in which cytochrome c plays a central role; recognizing several cytosolic and nuclear targets upon its release from the mitochondria. Whilst cytochrome c inhibits histone chaperones – to impair chromatin remodeling – in the nucleus of human and plant cells, the relevance of its cytosolic interactions in both organisms remains obscure, beyond the well-known apoptosome activation in humans. Here, the functional implications of the interaction between human cytochrome c and its cytosolic target 14-3-3 (an apoptosome assembly modulator) have been studied in depth. This PhD thesis has unveiled that cytochrome c impairs the 14-3-3-mediated inhibition of Apaf-1, thus promoting the activation of the latter to trigger programmed cell death. In addition, phosphorylation of Apaf-1 can modulate such novel regulatory mechanism to diminish death signaling. Furthermore, biophysical and structural approaches have been used to provide the molecular basis for the interaction between cytochrome c and 14-3-3. The research presented in this PhD thesis has also revealed the plant 14-3-3 isoform – the closest related analogue to human 14-3-3 as an inhibitor of programmed cell death proteases. In cell studies have shown 14- 3-3 recognizes plant cytochrome c during cell death, while in vitro approaches have evidenced similar recognition surfaces and thermodynamic parameters between this plant complex and its human analogue. These similarities have also been observed for heterologous complexes comprised of human and plant cytochrome c with 14-3-3 and 14-3-3, respectively. In summary, the interactions of cytochrome c with 14-3-3 family members have elucidated novel cytosolic functions of these proteins during human and plant programmed cell death. This demonstrates great evolutionary similarities between the protein networks controlling these processes in both organisms.