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

Higher-order plants and mammals use similar mechanisms to repair and tolerate oxidative DNA damage. Most studies on the DNA repair process have focused on yeast and mammals, in which histone chaperone-mediated nucleosome disassembly/reassembly is essential for DNA to be accessible to repair machinery. However, little is known about the specific role and modulation of histone chaperones in the context of DNA damage in plants. Here, the histone chaperone NRP1, which is closely related to human SET/TAF-I, was found to exhibit nucleosome assembly activity in vitro and to accumulate in the chromatin of Arabidopsis thaliana after DNA breaks. In addition, this work establishes that NRP1 binds to cytochrome c, thereby preventing the former from binding to histones. Since NRP1 interacts with cytochrome c at its earmuff domain, that is, its histone-binding domain, cytochrome c thus competes with core histones and hampers the activity of NRP1 as a histone chaperone. Altogether, the results obtained indicate that the underlying molecular mechanisms in nucleosome disassembly/reassembly are highly conserved throughout evolution, as inferred from the similar inhibition of plant NRP1 and human SET/TAF-I by cytochrome c during DNA damage response

Structural basis for inhibition of the histone chaperone activity of SET/TAF-Iß by cytochrome c

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 re- gulators 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 chap- erone SET/TAF-Iß 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-Iß to core histones, thereby locking its histone-binding domains and inhibiting its nucle- osome assembly activity. In addition, we have used NMR spectros- copy, 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-Iß. Overall, these findings estab- lish a framework for understanding the molecular basis of cyto- chrome c-mediated blocking of SET/TAF-Iß, which subsequently may facilitate the development of new drugs to silence the oncogenic effect of SET/TAF-Iß’s histone chaperone activity

Cytochrome c speeds up caspase cascade activation by blocking 14-3-3¿-dependent Apaf-1 inhibition article

Apoptosis is a highly regulated form of programmed cell death, essential to the development and homeostasis of multicellular organisms. Cytochrome c is a central figure in the activation of the apoptotic intrinsic pathway, thereby activating the caspase cascade through its interaction with Apaf-1. Our recent studies have revealed 14-3-3€ (a direct inhibitor of Apaf-1) as a cytosolic cytochrome c target. Here we explore the cytochrome c / 14-3-3€ interaction and show the ability of cytochrome c to block 14-3-3€-mediated Apaf-1 inhibition, thereby unveiling a novel function for cytochrome c as an indirect activator of caspase-9/3. We have used calorimetry, NMR spectroscopy, site mutagenesis and computational calculations to provide an insight into the structural features of the cytochrome c / 14-3-3€ complex. Overall, these findings suggest an additional cytochrome c-mediated mechanism to modulate apoptosome formation, shedding light onto the rigorous apoptotic regulation network

Inhibition of the PP2A activity by the histone chaperone ANP32B is long-range allosterically regulated by respiratory cytochrome c

Repair of injured DNA relies on nucleosome dismantling by histone chaperones and de-phosphorylation events carried out by Protein Phosphatase 2A (PP2A). Typical histone chaperones are the Acidic leucine-rich Nuclear Phosphoprotein 32 family (ANP32) members, e.g. ANP32A, which is also a well-known PP2A inhibitor (a.k.a. I1PP2A). Here we report the novel interaction between the endogenous family member B—so-called ANP32B—and endogenous cytochrome c in cells undergoing camptothecin-induced DNA damage. Soon after DNA lesions but prior to caspase cascade activation, the hemeprotein translocates to the nucleus to target the Low Complexity Acidic Region (LCAR) of ANP32B; in a similar way, our group recently reported that the hemeprotein targets the acidic domain of SET/Template Activating Factor-Iß (SET/TAF-Iß), which is another histone chaperone and PP2A inhibitor (a.k.a. I2PP2A). The nucleosome assembly activity of ANP32B is indeed unaffected by cytochrome c binding. Like ANP32A, ANP32B inhibits PP2A activity and is thus herein referred to as I3PP2A. Our data demonstrates that ANP32B-dependent inhibition of PP2A is regulated by respiratory cytochrome c, which induces long-distance allosteric changes in the structured N-terminal domain of ANP32B upon binding to the C-terminal LCAR. In agreement with the reported role of PP2A in the DNA damage response, we propose a model wherein cytochrome c is translocated from the mitochondria into the nucleus upon DNA damage to modulate PP2A activity via its interaction with ANP32B. © 2021 The Author(s

PP2A is activated by cytochrome c upon formation of a diffuse encounter complex with SET/TAF-Iß

Intrinsic protein flexibility is of overwhelming relevance for intermolecular recognition and adaptability of highly dynamic ensemble of complexes, and the phenomenon is essential for the understanding of numerous biological processes. These conformational ensembles—encounter complexes—lack a unique organization, which prevents the determination of well-defined high resolution structures. This is the case for complexes involving the oncoprotein SET/template-activating factor-Iß (SET/TAF-Iß), a histone chaperone whose functions and interactions are significantly affected by its intrinsic structural plasticity. Besides its role in chromatin remodeling, SET/TAF-Iß is an inhibitor of protein phosphatase 2A (PP2A), which is a key phosphatase counteracting transcription and signaling events controlling the activity of DNA damage response (DDR) mediators. During DDR, SET/TAF-Iß is sequestered by cytochrome c (Cc) upon migration of the hemeprotein from mitochondria to the cell nucleus. Here, we report that the nuclear SET/TAF-Iß:Cc polyconformational ensemble is able to activate PP2A. In particular, the N-end folded, globular region of SET/TAF-Iß (a.k.a. SET/TAF-Iß ¿C)—which exhibits an unexpected, intrinsically highly dynamic behavior—is sufficient to be recognized by Cc in a diffuse encounter manner. Cc-mediated blocking of PP2A inhibition is deciphered using an integrated structural and computational approach, combining small-angle X-ray scattering, electron paramagnetic resonance, nuclear magnetic resonance, calorimetry and molecular dynamics simulations

Developing energy efficient lignin biomass processing: towards understanding mediator behaviour in ionic liquids

Environmental concerns have brought attention to the requirement for more efficient and renewable processes for chemicals production. Lignin is the second most abundant natural polymer, and might serve as a sustainable resource for manufacturing fuels and aromatic derivatives for the chemicals industry after being depolymerised. In this work, the mediator 2,2′-azino-bis(3-ethylbenthiazoline-6-sulfonic acid) diammonium salt (ABTS), commonly used with enzyme degradation systems, has been evaluated by means of cyclic voltammetry (CV) for enhancing the oxidation of the non-phenolic lignin model compound veratryl alcohol and three types of lignin (organosolv, Kraft and lignosulfonate) in the ionic liquid 1-ethyl-3-methylimidazolium ethyl sulfate, ([C2mim][C2SO4]). The presence of either veratryl alcohol or organosolv lignin increased the second oxidation peak of ABTS under select conditions, indicating the ABTS-mediated oxidation of these molecules at high potentials in [C2mim][C2SO4]. Furthermore, CV was applied as a quick and efficient way to explore the impact of water in the ABTS-mediated oxidation of both organosolv and lignosulfonate lignin. Higher catalytic efficiencies of ABTS were observed for lignosulfonate solutions either in sodium acetate buffer or when [C2mim][C2SO4] (15 v/v%) was present in the buffer solution, whilst there was no change found in the catalytic efficiency of ABTS in [C2mim][C2SO4]–lignosulfonate mixtures relative to ABTS alone. In contrast, organosolv showed an initial increase in oxidation, followed by a significant decrease on increasing the water content of a [C2mim][C2SO4] solution

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

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.Peer reviewe

Early attack and subsequent changes produced in an industrial lignin by a fungal laccase and a laccase-mediator system: an analytical approach

An industrial kraft pine lignin (Indulin AT, KL) was characterized and treated in both aqueous-buffered media and dioxane to water, either with a partially purified laccase from Fusarium proliferatum or with the laccase plus 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic-acid (ABTS) as mediator. The changes in the lignin after different incubation periods were analyzed through the application of high performance liquid chromatography (HPLC), UV-visible (Vis) spectroscopy and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). At the onset of incubation, laccase-treated samples showed a slight polymerization and strong modifications in UV-Vis spectra. Through Py-GC/MS, a decrease in phenolic and methoxy-bearing pyrolysis products was observed, in contrast to an increase in the more oxidized products. After longer incubation periods (48 h) a substantial polymerization was detected by HPLC, along with a decrease in the guaiacyl (G) units. In contrast, the analysis by HPLC of the samples recovered from the laccase-ABTS system (LMS) showed an intense depolymerization, accompanied by a sizeable loss in G units and a decrease in the methyl and ethyl side-chain phenolic compounds. These results provide conclusive evidence of a rapid initial attack of the industrial lignin by laccase and notable modifications in the KL after longer incubation periods with laccase or LMS. © 2006 Springer-Verlag.This work was supported partially by the projects PI 2002/064 (Gobierno Autónomo de Canarias) and REN 2002-02732/TECNO (MCT).Peer Reviewe

Guiding light with singular beams in nanoplasmonic colloids

We investigate the nonlinear propagation of light beams with complex phase and intensity structures, including a Gaussian-embedded vortex, a Bessel vortex, and a Bessel-cosine necklace. We employ a colloidal suspension of bio-synthesized plasmonic gold nanoparticles, where a self-defocusing response is mediated by absorption at the laser wavelength (532 nm). We show that, by means of nonlocal nonlinearity, these structured two-dimensional beams with on-axis singularity can counteract the diffraction of the dark core and guide therein a coaxial Gaussian probe of different wavelengths (633 nm) and lower intensities. Angular steering of the confined probe is also demonstrated by tilting the propagation direction of the pump