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