Structural basis for inhibition of the histone chaperone activity of SET/TAF-Iβ by cytochromec

Abstract

Chromatin is pivotal for regulation of the DNA damage process insofar as it influences access to DNA and serves as a DNA repair docking site. Recent works identify histone chaperones as key regulators of damaged chromatin’s transcriptional activity. However, understanding how chaperones are modulated during DNA damage response is still challenging. This study reveals that the histone chaperone SET/TAF-Iβ interacts with cytochrome c following DNA damage. Specifically, cytochrome c is shown to be translocated into cell nuclei upon induction of DNA damage, but not upon stimulation of the death receptor or stress-induced pathways. Cytochrome c was found to competitively hinder binding of SET/TAF-Iβ to core histones, thereby locking its histone-binding domains and inhibiting its nucleosome assembly activity. In addition, we have used NMR spectroscopy, calorimetry, mutagenesis, and molecular docking to provide an insight into the structural features of the formation of the complex between cytochrome c and SET/TAF-Iβ. Overall, these findings establish a framework for understanding the molecular basis of cytochrome c-mediated blocking of SET/TAF-Iβ, which subsequently may facilitate the development of new drugs to silence the oncogenic effect of SET/TAF-Iβ’s histone chaperone activity.

Histone chaperone activity of Arabidopsis thaliana NRP1 is blocked by cytochrome c

“…This latter finding is in agreement with previous works in which lysine residues were found to be involved in the binding of C c to cytochrome b c 1 (44,68,71,72), cytochrome c oxidase (67) and GALDH (49), as well as to partners in apoptosis like Apaf-1 (73) and SET/TAF-Iβ (40). …”

“…Taking into account the close relation between A. thaliana NRP1 and human SET/TAF-Iβ (Figure 2A), the similar histone-binding properties of the two, and the fact that human C c was recently described as affecting the ability of SET/TAF-Iβ to bind to histones (40), experiments were carried out to determine if C c affects NRP1 in a similar way.…”

“…Taking into account that NRP1 and SET/TAF-Iβ are targeted by C c in both plant and human cells upon DNA damage (35,39), thereby blocking their ability to act as histone chaperones (40), it is tempting to hypothesize a similar role for such inhibition in both organisms.…”

Structural basis of mitochondrial dysfunction in response to cytochrome c phosphorylation at tyrosine 48

“…In addition, Cc aids in controlling ROS levels by oxidizing superoxide anions (11) and exhibiting peroxidase activity (12); the latter, however, also yields lipid peroxidation (13,14). Furthermore, Cc plays a crucial role in programmed cell death, a process that is only partially understood (15)(16)(17)(18)(19)(20)(21). In this context, a fraction of Cc binds and oxidizes cardiolipin (CL) at the internal mitochondrial membrane, thereby facilitating the release of unbound Cc to the cytoplasm (16,17).…”

“…In mammalian cells, extramitochondrial Cc interacts with apoptosis activating factor 1 (Apaf-1) in the cytoplasm to spark the caspase proteolytic cascade (15). It has recently been shown that Cc can interact with several other proteins outside the mitochondria in humans and plants (18)(19)(20)(21). The similarities between the Cc signaling networks in both organisms suggest that key programmed cell-death pathways are conserved throughout evolution (22).…”