Identification of a Region in the Common Amino-terminal Domain of Hendra Virus P, V, and W Proteins Responsible for Phase Transition and Amyloid Formation.

Henipaviruses are BSL-4 zoonotic pathogens responsible in humans for severe encephalitis. Their V protein is a key player in the evasion of the host innate immune response. We previously showed that the Henipavirus V proteins consist of a long intrinsically disordered N-terminal domain (NTD) and a ß-enriched C-terminal domain (CTD). These terminals are critical for V binding to DDB1, which is a cellular protein that is a component of the ubiquitin ligase E3 complex, as well as binding to MDA5 and LGP2, which are two host sensors of viral RNA. Here, we serendipitously discovered that the Hendra virus V protein undergoes a liquid-to-hydrogel phase transition and identified the V region responsible for this phenomenon. This region, referred to as PNT3 and encompassing residues 200-310, was further investigated using a combination of biophysical and structural approaches. Congo red binding assays, together with negative-staining transmisison electron microscopy (TEM) studies, show that PNT3 forms amyloid-like fibrils. Fibrillation abilities are dramatically reduced in a rationally designed PNT3 variant in which a stretch of three contiguous tyrosines, falling within an amyloidogenic motif, were replaced by three alanines. Worthy to note, Congo red staining experiments provided hints that these amyloid-like fibrils form not only in vitro but also in cellula after transfection or infection. The present results set the stage for further investigations aimed at assessing the functional role of phase separation and fibrillation by the Henipavirus V proteins.

A Comparative Analysis of the In Vitro Anticancer Activity of Iridium(III) {η5-C5Me4R} Complexes with Variable R Groups.

Piano-stool iridium complexes based on the pentamethylcyclopentadienyl ligand (Cp*) have been intensively investigated as anticancer drug candidates and hold much promise in this setting. A systematic study aimed at outlining the effect of Cp* mono-derivatization on the antiproliferative activity is presented here. Thus, the dinuclear complexes [Ir(η5-C5Me4R)Cl(µ-Cl)]2 (R = Me, 1a; R = H, 1b; R = Pr, 1c; R = 4-C6H4F, 1d; R = 4-C6H4OH, 1e), their 2-phenylpyridyl mononuclear derivatives [Ir(η5-C5Me4R)(kN,kCPhPy)Cl] (2a-d), and the dimethylsulfoxide complex [Ir{η5-C5Me4(4-C6H4OH)}Cl2(κS-Me2S=O)] (3) were synthesized, structurally characterized, and assessed for their cytotoxicity towards a panel of six human and rodent cancer cell lines (mouse melanoma, B16; rat glioma, C6; breast adenocarcinoma, MCF-7; colorectal carcinoma, SW620 and HCT116; ovarian carcinoma, A2780) and one primary, human fetal lung fibroblast cell line (MRC5). Complexes 2b (R = H) and 2d (4-C6H4F) emerged as the most active ones and were selected for further investigation. They did not affect the viability of primary mouse peritoneal cells, and their tumoricidal action arises from the combined influence on cellular proliferation, apoptosis and senescence. The latter is triggered by mitochondrial failure and production of reactive oxygen and nitrogen species.

Ensemble description of the intrinsically disordered N-terminal domain of the Nipah virus P/V protein from combined NMR and SAXS.

Using SAXS and NMR spectroscopy, we herein provide a high-resolution description of the intrinsically disordered N-terminal domain (PNT, aa 1-406) shared by the Nipah virus (NiV) phosphoprotein (P) and V protein, two key players in viral genome replication and in evasion of the host innate immune response, respectively. The use of multidimensional NMR spectroscopy allowed us to assign as much as 91% of the residues of this intrinsically disordered domain whose size constitutes a technical challenge for NMR studies. Chemical shifts and nuclear relaxation measurements provide the picture of a highly flexible protein. The combination of SAXS and NMR information enabled the description of the conformational ensemble of the protein in solution. The present results, beyond providing an overall description of the conformational behavior of this intrinsically disordered region, also constitute an asset for obtaining atomistic information in future interaction studies with viral and/or cellular partners. The present study can thus be regarded as the starting point towards the design of inhibitors that by targeting crucial protein-protein interactions involving PNT might be instrumental to combat this deadly virus.

Adenoviral E1A Exploits Flexibility and Disorder to Target Cellular Proteins.

Direct interaction between intrinsically disordered proteins (IDPs) is often difficult to characterize hampering the elucidation of their binding mechanism. Particularly challenging is the study of fuzzy complexes, in which the intrinsically disordered proteins or regions retain conformational freedom within the assembly. To date, nuclear magnetic resonance spectroscopy has proven to be one of the most powerful techniques to characterize at the atomic level intrinsically disordered proteins and their interactions, including those cases where the formed complexes are highly dynamic. Here, we present the characterization of the interaction between a viral protein, the Early region 1A protein from Adenovirus (E1A), and a disordered region of the human CREB-binding protein, namely the fourth intrinsically disordered linker CBP-ID4. E1A was widely studied as a prototypical viral oncogene. Its interaction with two folded domains of CBP was mapped, providing hints for understanding some functional aspects of the interaction with this transcriptional coactivator. However, the role of the flexible linker connecting these two globular domains of CBP in this interaction was never explored before.

Monitoring the Interaction of α-Synuclein with Calcium Ions through Exclusively Heteronuclear Nuclear Magnetic Resonance Experiments.

Many properties of intrinsically disordered proteins (IDPs), or protein regions (IDRs), are modulated by the nature of amino acid side chains as well as by local solvent exposure. We propose a set of exclusively heteronuclear NMR experiments to investigate these features in different experimental conditions that are relevant for physiological function. The proposed approach is generally applicable to many IDPs/IDRs whose assignment is available in the Biological Magnetic Resonance Bank (BMRB) to investigate how their properties are modulated by different, physiologically relevant conditions. The experiments, tested on α-synuclein, are then used to investigate how α-synuclein senses Ca2+ concentration jumps associated with the transmission of nerve signals. Novel modules in the primary sequence of α-synuclein optimized for calcium sensing in highly flexible, disordered protein segments are identified.

Taking Simultaneous Snapshots of Intrinsically Disordered Proteins in Action.

Intrinsically disordered proteins (IDPs) as well as intrinsically disordered regions (IDRs) of complex protein machineries have recently been recognized as key players in many cellular functions. NMR represents a unique tool to access atomic resolution structural and dynamic information on highly flexible IDPs/IDRs. Improvements in instrumental sensitivity made heteronuclear direct detection possible for biomolecular NMR applications. The CON experiment has become one of the most useful NMR experiments to get a snapshot of an IDP/IDR in conditions approaching physiological ones. The availability of NMR spectrometers equipped with multiple receivers now enables the acquisition of several experiments simultaneously instead of one after the other. Here, we propose several variants of the CON experiment in which, during the recovery delay, a second two-dimensional experiment is acquired, either based on 1H detection (CON//HN) or on 15N detection (CON//btNH, CON//(H)CAN). The possibility to collect simultaneous snapshots of an IDP/IDR through different two-dimensional spectra provides a novel tool to follow chemical reactions, such as the occurrence of posttranslational modifications, as well as to study samples of limited lifetime such as cell lysates or whole cells.

Cyclized NDGA modifies dynamic α-synuclein monomers preventing aggregation and toxicity.

Growing evidence implicates α-synuclein aggregation as a key driver of neurodegeneration in Parkinson's disease (PD) and other neurodegenerative disorders. Herein, the molecular and structural mechanisms of inhibiting α-synuclein aggregation by novel analogs of nordihydroguaiaretic acid (NDGA), a phenolic dibenzenediol lignan, were explored using an array of biochemical and biophysical methodologies. NDGA analogs induced modest, progressive compaction of monomeric α-synuclein, preventing aggregation into amyloid-like fibrils. This conformational remodeling preserved the dynamic adoption of α-helical conformations, which are essential for physiological membrane interactions. Oxidation-dependent NDGA cyclization was required for the interaction with monomeric α-synuclein. NDGA analog-pretreated α-synuclein did not aggregate even without NDGA-analogs in the aggregation mixture. Strikingly, NDGA-pretreated α-synuclein suppressed aggregation of naïve untreated aggregation-competent monomeric α-synuclein. Further, cyclized NDGA reduced α-synuclein-driven neurodegeneration in Caenorhabditis elegans. The cyclized NDGA analogs may serve as a platform for the development of small molecules that stabilize aggregation-resistant α-synuclein monomers without interfering with functional conformations yielding potential therapies for PD and related disorders.

Proline Fingerprint in Intrinsically Disordered Proteins.

NMR spectroscopy is one of the main techniques used for high-resolution studies of intrinsically disordered proteins (IDPs), permitting mapping of the structural and dynamic features of all the amino acids constituting the polypeptide at atomic resolution. Only proline residues are less straightforward to characterize because they lack any amide proton, thus rendering them not directly visible in the commonly used 2D 1 H,15 N correlation experiments. However, proline residues are highly abundant in IDPs and can mediate important functions. In this work we present an easy and effective way to obtain fingerprints of proline residues in IDPs at high resolution.

13C APSY-NMR for sequential assignment of intrinsically disordered proteins.

The increasingly recognized biological relevance of intrinsically disordered proteins requires a continuous expansion of the tools for their characterization via NMR spectroscopy, the only technique so far able to provide atomic-resolution information on these highly mobile macromolecules. Here we present the implementation of projection spectroscopy in 13C-direct detected NMR experiments to achieve the sequence specific assignment of IDPs. The approach was used to obtain the complete backbone assignment at high temperature of α-synuclein, a paradigmatic intrinsically disordered protein.

The chlorinating behaviour of WCl6 towards α-aminoacids.

Cl/O interchange took place when WCl6 was allowed to interact with a series of α-aminoacids. The α-ammonium-acylchloride salts [NH2(CH2)3CHC(O)Cl][WOCl5], 1a, and [MeNH2CH2C(O)Cl][WOCl5], 1b, were afforded in ca. 55% yields from the reactions of WCl6 with, respectively, L-proline and sarcosine in CH2Cl2. By using other reaction media (hexane or CHCl3), the α-amino-acylchloride complexes WOCl4[O=C(Cl)CH(CH2)3NH2], 5a, and WOCl4[O=C(Cl)CH(R)NHR'] (R = H, R' = Me, 5b; R = R' = H, 5c; R = Me, R' = H, 5d) were isolated in moderate to good yields from WCl6 and, respectively, L-proline, sarcosine, glycine and L-alanine. The formation of 5a,b is basically the result of HCl release from the parent compounds 1a,b. 5a represents a key intermediate in the course of the reaction leading to (WOCl4)2[µ:κ(2)(O)-dkp], 2, dkp = (S,S)-octahydrodipyrrolo[1,2-a:1',2'-d]pyrazine-5,10-dione. 2 was optimally prepared from WCl6/L-proline under high temperature conditions. Hydrolytic treatment of 2 afforded the L-proline-derived 2,5-diketopiperazine (dkp), which was finally isolated with an overall yield of 70%. 1a,b were characterized by X-ray diffractometry, thus providing very rare examples of crystallographically characterized acylchloride derivatives of α-aminoacids. DFT calculations were extensively carried out in order to shed light on structural and mechanistic features.