The Dimorphos ejecta plume properties revealed by LICIACube

The Double Asteroid Redirection Test (DART) had an impact with Dimorphos (a satellite of the asteroid Didymos) on 26 September 20221. Ground-based observations showed that the Didymos system brightened by a factor of 8.3 after the impact because of ejecta, returning to the pre-impact brightness 23.7 days afterwards2. Hubble Space Telescope observations made from 15 minutes after impact to 18.5 days after, with a spatial resolution of 2.1 kilometres per pixel, showed a complex evolution of the ejecta3, consistent with other asteroid impact events. The momentum enhancement factor, determined using the measured binary period change4, ranges between 2.2 and 4.9, depending on the assumptions about the mass and density of Dimorphos5. Here we report observations from the LUKE and LEIA instruments on the LICIACube cube satellite, which was deployed 15 days in advance of the impact of DART. Data were taken from 71 seconds before the impact until 320 seconds afterwards. The ejecta plume was a cone with an aperture angle of 140 ± 4 degrees. The inner region of the plume was blue, becoming redder with increasing distance from Dimorphos. The ejecta plume exhibited a complex and inhomogeneous structure, characterized by filaments, dust grains and single or clustered boulders. The ejecta velocities ranged from a few tens of metres per second to about 500 metres per second.

Natural Inhibitors of Amyloid Aggregation

Amyloid aggregates are diverse proteinaceous assemblies, including one or more protein species, wherein the molecules interact according to characteristic patterns [...].

Exploring the Interior of Europa with the Europa Clipper

The Galileo mission to Jupiter revealed that Europa is an ocean world. The Galileo magnetometer experiment in particular provided strong evidence for a salty subsurface ocean beneath the ice shell, likely in contact with the rocky core. Within the ice shell and ocean, a number of tectonic and geodynamic processes may operate today or have operated at some point in the past, including solid ice convection, diapirism, subsumption, and interstitial lake formation. The science objectives of the Europa Clipper mission include the characterization of Europa's interior; confirmation of the presence of a subsurface ocean; identification of constraints on the depth to this ocean, and on its salinity and thickness; and determination of processes of material exchange between the surface, ice shell, and ocean. Three broad categories of investigation are planned to interrogate different aspects of the subsurface structure and properties of the ice shell and ocean: magnetic induction, subsurface radar sounding, and tidal deformation. These investigations are supplemented by several auxiliary measurements. Alone, each of these investigations will reveal unique information. Together, the synergy between these investigations will expose the secrets of the Europan interior in unprecedented detail, an essential step in evaluating the habitability of this ocean world.

Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos

The NASA Double Asteroid Redirection Test (DART) mission performed a kinetic impact on asteroid Dimorphos, the satellite of the binary asteroid (65803) Didymos, at 23:14 UTC on 26 September 2022 as a planetary defence test1. DART was the first hypervelocity impact experiment on an asteroid at size and velocity scales relevant to planetary defence, intended to validate kinetic impact as a means of asteroid deflection. Here we report a determination of the momentum transferred to an asteroid by kinetic impact. On the basis of the change in the binary orbit period2, we find an instantaneous reduction in Dimorphos's along-track orbital velocity component of 2.70 ± 0.10 mm s-1, indicating enhanced momentum transfer due to recoil from ejecta streams produced by the impact3,4. For a Dimorphos bulk density range of 1,500 to 3,300 kg m-3, we find that the expected value of the momentum enhancement factor, β, ranges between 2.2 and 4.9, depending on the mass of Dimorphos. If Dimorphos and Didymos are assumed to have equal densities of 2,400 kg m-3, [Formula: see text]. These β values indicate that substantially more momentum was transferred to Dimorphos from the escaping impact ejecta than was incident with DART. Therefore, the DART kinetic impact was highly effective in deflecting the asteroid Dimorphos.

The Vault Nanoparticle: A Gigantic Ribonucleoprotein Assembly Involved in Diverse Physiological and Pathological Phenomena and an Ideal Nanovector for Drug Delivery and Therapy

Simple Summary

In recent decades, a molecular complex referred to as vault nanoparticle has attracted much attention by the scientific community, due to its unique properties. At the molecular scale, it is a huge assembly consisting of 78 97-kDa polypeptide chains enclosing an internal cavity, wherein enzymes involved in DNA integrity maintenance and some small noncoding RNAs are accommodated. Basically, two reasons justify this interest. On the one hand, this complex represents an ideal tool for the targeted delivery of drugs, provided it is suitably engineered, either chemically or genetically; on the other hand, it has been shown to be involved in several cellular pathways and mechanisms that most often result in multidrug resistance. It is therefore expected that a better understanding of the physiological roles of this ribonucleoproteic complex may help develop new therapeutic strategies capable of coping with cancer progression. Here, we provide a comprehensive review of the current knowledge.

Abstract

The vault nanoparticle is a eukaryotic ribonucleoprotein complex consisting of 78 individual 97 kDa-“major vault protein” (MVP) molecules that form two symmetrical, cup-shaped, hollow halves. It has a huge size (72.5 × 41 × 41 nm) and an internal cavity, wherein the vault poly(ADP-ribose) polymerase (vPARP), telomerase-associated protein-1 (TEP1), and some small untranslated RNAs are accommodated. Plenty of literature reports on the biological role(s) of this nanocomplex, as well as its involvement in diseases, mostly oncological ones. Nevertheless, much has still to be understood as to how vault participates in normal and pathological mechanisms. In this comprehensive review, current understanding of its biological roles is discussed. By different mechanisms, vault’s individual components are involved in major cellular phenomena, which result in protection against cellular stresses, such as DNA-damaging agents, irradiation, hypoxia, hyperosmotic, and oxidative conditions. These diverse cellular functions are accomplished by different mechanisms, mainly gene expression reprogramming, activation of proliferative/prosurvival signaling pathways, export from the nucleus of DNA-damaging drugs, and import of specific proteins. The cellular functions of this nanocomplex may also result in the onset of pathological conditions, mainly (but not exclusively) tumor proliferation and multidrug resistance. The current understanding of its biological roles in physiological and pathological processes should also provide new hints to extend the scope of its exploitation as a nanocarrier for drug delivery.

Measurement and implications of Saturn’s gravity field and ring mass

The interior structure of Saturn, the depth of its winds, and the mass and age of its rings constrain its formation and evolution. In the final phase of the Cassini mission, the spacecraft dived between the planet and its innermost ring, at altitudes of 2600 to 3900 kilometers above the cloud tops. During six of these crossings, a radio link with Earth was monitored to determine the gravitational field of the planet and the mass of its rings. We find that Saturn’s gravity deviates from theoretical expectations and requires differential rotation of the atmosphere extending to a depth of at least 9000 kilometers. The total mass of the rings is (1.54 ± 0.49) × 1019 kilograms (0.41 ± 0.13 times that of the moon Mimas), indicating that the rings may have formed 107 to 108 years ago.

Targeting Amyloid Aggregation: An Overview of Strategies and Mechanisms

Amyloids result from the aggregation of a set of diverse proteins, due to either specific mutations or promoting intra- or extra-cellular conditions. Structurally, they are rich in intermolecular β-sheets and are the causative agents of several diseases, both neurodegenerative and systemic. It is believed that the most toxic species are small aggregates, referred to as oligomers, rather than the final fibrillar assemblies. Their mechanisms of toxicity are mostly mediated by aberrant interactions with the cell membranes, with resulting derangement of membrane-related functions. Much effort is being exerted in the search for natural antiamyloid agents, and/or in the development of synthetic molecules. Actually, it is well documented that the prevention of amyloid aggregation results in several cytoprotective effects. Here, we portray the state of the art in the field. Several natural compounds are effective antiamyloid agents, notably tetracyclines and polyphenols. They are generally non-specific, as documented by their partially overlapping mechanisms and the capability to interfere with the aggregation of several unrelated proteins. Among rationally designed molecules, we mention the prominent examples of β-breakers peptides, whole antibodies and fragments thereof, and the special case of drugs with contrasting transthyretin aggregation. In this framework, we stress the pivotal role of the computational approaches. When combined with biophysical methods, in several cases they have helped clarify in detail the protein/drug modes of interaction, which makes it plausible that more effective drugs will be developed in the future.

Protein Environment: A Crucial Triggering Factor in Josephin Domain Aggregation: The Role of 2,2,2-Trifluoroethanol

The protein ataxin-3 contains a polyglutamine stretch that triggers amyloid aggregation when it is expanded beyond a critical threshold. This results in the onset of the spinocerebellar ataxia type 3. The protein consists of the globular N-terminal Josephin domain and a disordered C-terminal tail where the polyglutamine stretch is located. Expanded ataxin-3 aggregates via a two-stage mechanism: first, Josephin domain self-association, then polyQ fibrillation. This highlights the intrinsic amyloidogenic potential of Josephin domain. Therefore, much effort has been put into investigating its aggregation mechanism(s). A key issue regards the conformational requirements for triggering amyloid aggregation, as it is believed that, generally, misfolding should precede aggregation. Here, we have assayed the effect of 2,2,2-trifluoroethanol, a co-solvent capable of stabilizing secondary structures, especially α-helices. By combining biophysical methods and molecular dynamics, we demonstrated that both secondary and tertiary JD structures are virtually unchanged in the presence of up to 5% 2,2,2-trifluoroethanol. Despite the preservation of JD structure, 1% of 2,2,2-trifluoroethanol suffices to exacerbate the intrinsic aggregation propensity of this domain, by slightly decreasing its conformational stability. These results indicate that in the case of JD, conformational fluctuations might suffice to promote a transition towards an aggregated state without the need for extensive unfolding, and highlights the important role played by the environment on the aggregation of this globular domain.

A fast and straightforward procedure for vault nanoparticle purification and the characterization of its endocytic uptake

BACKGROUND

Vaults are eukaryotic ribonucleoprotein particles composed of up 78 copies of the 97 kDa major vault protein that assembles into a barrel-like, "nanocapsule" enclosing poly(ADP-ribose) polymerase, telomerase-associated protein-1 and small untranslated RNAs. Overall, the molecular mass of vault particles amounts to about 13 MDa. Although it has been implicated in several cellular functions, its physiological roles remain poorly understood. Also, the possibility to exploit it as a nanovector for drug delivery is currently being explored in several laboratories.

METHODS

Using the baculovirus expression system, vaults were expressed and purified by a dialysis step using a 1 MDa molecular weight cutoff membrane and a subsequent size exclusion chromatography. Purity was assessed by SDS-PAGE, transmission electron microscopy and dynamic light scattering. Particle's endocytic uptake was monitored by flow cytometry and confocal microscopy.

RESULTS

The purification protocol here reported is far simpler and faster than those currently available and lead to the production of authentic vault. We then demonstrated its clathrin-mediated endocytic uptake by normal fibroblast and glioblastoma, but not carcinoma cell lines. In contrast, no significant caveolin-mediated endocytosis was detected.

CONCLUSIONS

These results provide the first evidence for an intrinsic propensity of the vault complex to undergo endocytic uptake cultured eukaryotic cells.

GENERAL SIGNIFICANCE

The newly developed purification procedure will greatly facilitate any investigation based on the use of the vault particle as a natural nanocarrier. Its clathrin-mediated endocytic uptake observed in normal and in some tumor cell lines sheds light on its physiological role.

Epigallocatechin-3-gallate and related phenol compounds redirect the amyloidogenic aggregation pathway of ataxin-3 towards non-toxic aggregates and prevent toxicity in neural cells and Caenorhabditis elegans animal model

The protein ataxin-3 (ATX3) triggers an amyloid-related neurodegenerative disease when its polyglutamine stretch is expanded beyond a critical threshold. We formerly demonstrated that the polyphenol epigallocatechin-3-gallate (EGCG) could redirect amyloid aggregation of a full-length, expanded ATX3 (ATX3-Q55) towards non-toxic, soluble, SDS-resistant aggregates. Here, we have characterized other related phenol compounds, although smaller in size, i.e. (-)-epigallocatechin gallate (EGC), and gallic acid (GA). We analysed the aggregation pattern of ATX3-Q55 and of the N-terminal globular Josephin domain (JD) by assessing the time course of the soluble protein, as well its structural features by FTIR and AFM, in the presence and the absence of the mentioned compounds. All of them redirected the aggregation pattern towards soluble, SDS-resistant aggregates. They also prevented the appearance of ordered side-chain hydrogen bonding in ATX3-Q55, which is the hallmark of polyQ-related amyloids. Molecular docking analyses on the JD highlighted three interacting regions, including the central, aggregation-prone one. All three compounds bound to each of them, although with different patterns. This might account for their capability to prevent amyloidogenesis. Saturation transfer difference NMR experiments also confirmed EGCG and EGC binding to monomeric JD. ATX3-Q55 pre-incubation with any of the three compounds prevented its calcium-influx-mediated cytotoxicity towards neural cells. Finally, all the phenols significantly reduced toxicity in a transgenic Caenorhabditis elegans strain expressing an expanded ATX3. Overall, our results show that the three polyphenols act in a substantially similar manner. GA, however, might be more suitable for antiamyloid treatments due to its simpler structure and higher chemical stability.

The polyglutamine protein ataxin-3 enables normal growth under heat shock conditions in the methylotrophic yeast Pichia pastoris

The protein ataxin-3 carries a polyglutamine stretch close to the C-terminus that triggers a neurodegenerative disease in humans when its length exceeds a critical threshold. A role as a transcriptional regulator but also as a ubiquitin hydrolase has been proposed for this protein. Here, we report that, when expressed in the yeast Pichia pastoris, full-length ataxin-3 enabled almost normal growth at 37 °C, well above the physiological optimum of 30 °C. The N-terminal Josephin domain (JD) was also effective but significantly less, whereas catalytically inactive JD was completely ineffective. Based on MudPIT proteomic analysis, we observed that the strain expressing full-length, functional ataxin-3 displayed persistent upregulation of enzymes involved in mitochondrial energy metabolism during growth at 37 °C compared with the strain transformed with the empty vector. Concurrently, in the transformed strain intracellular ATP levels at 37 °C were even higher than normal ones at 30 °C. Elevated ATP was also paralleled by upregulation of enzymes involved in both protein biosynthesis and biosynthetic pathways, as well as of several stress-induced proteins. A similar pattern was observed when comparing a strain expressing JD with another expressing its catalytically inactive counterpart. We suggest that such effects mostly result from mechanisms of transcriptional regulation.

Negatively charged silver nanoparticles with potent antibacterial activity and reduced toxicity for pharmaceutical preparations

Background

The discovery of new solutions with antibacterial activity as efficient and safe alternatives to common preservatives (such as parabens) and to combat emerging infections and drug-resistant bacterial pathogens is highly expected in cosmetics and pharmaceutics. Colloidal silver nanoparticles (NPs) are attracting interest as novel effective antimicrobial agents for the prevention of several infectious diseases.

Methods

Water-soluble, negatively charged silver nanoparticles (AgNPs) were synthesized by reduction with citric and tannic acid and characterized by transmission electron microscopy, dynamic light scattering, zeta potential, differential centrifuge sedimentation, and ultraviolet–visible spectroscopy. AgNPs were tested with model Gram-negative and Gram-positive bacteria in comparison to two different kinds of commercially available AgNPs.

Results

In this work, AgNPs with higher antibacterial activity compared to the commercially available colloidal silver solutions were prepared and investigated. Bacteria were plated and the antibacterial activity was tested at the same concentration of silver ions in all samples. The AgNPs did not show any significant reduction in the antibacterial activity for an acceptable time period. In addition, AgNPs were transferred to organic phase and retained their antibacterial efficacy in both aqueous and nonaqueous media and exhibited no toxicity in eukaryotic cells.

Conclusion

We developed AgNPs with a 20 nm diameter and negative zeta potential with powerful antibacterial activity and low toxicity compared to currently available colloidal silver, suitable for cosmetic preservatives and pharmaceutical preparations administrable to humans and/or animals as needed.

Inhibition of α-Synuclein Fibril Elongation by Hsp70 Is Governed by a Kinetic Binding Competition between α-Synuclein Species

The Hsp70 family of chaperones plays an essential role in suppressing protein aggregation in the cell. Here we investigate the factors controlling the intrinsic ability of human Hsp70 to inhibit the elongation of amyloid fibrils formed by the Parkinson's disease-related protein α-synuclein. Using kinetic analysis, we show that Hsp70 binds preferentially to α-synuclein fibrils as a consequence of variations in the association and dissociation rate constants of binding to the different aggregated states of the protein. Our findings illustrate the importance of the kinetics of binding of molecular chaperones, and also of potential therapeutic molecules, in the efficient suppression of specific pathogenic events linked to neurodegeneration.

How Epigallocatechin-3-gallate and Tetracycline Interact with the Josephin Domain of Ataxin-3 and Alter Its Aggregation Mode

Epigallocatechin-3-gallate (EGCG) and tetracycline are two known inhibitors of amyloid aggregation able to counteract the fibrillation of most of the proteins involved in neurodegenerative diseases. We have recently investigated their effect on ataxin-3 (AT3), the polyglutamine-containing protein responsible for spinocerebellar ataxia type 3. We previously showed that EGCG and tetracycline can contrast the aggregation process and toxicity of expanded AT3, although by different mechanisms. Here, we have performed further experiments by using the sole Josephin domain (JD) to further elucidate the mechanism of action of the two compounds. By protein solubility assays and FTIR spectroscopy we have first observed that EGCG and tetracycline affect the JD aggregation essentially in the same way displayed when acting on the full-length expanded AT3. Then, by saturation transfer difference (STD) NMR experiments, we have shown that EGCG binds both the monomeric and the oligomeric JD form, whereas tetracycline can only interact with the oligomeric one. Surface plasmon resonance (SPR) analysis has confirmed the capability of the sole EGCG to bind monomeric JD, although with a KD value suggestive for a non-specific interaction. Our investigations provide new details on the JD interaction with EGCG and tetracycline, which could explain the different mechanisms by which the two compounds reduce the toxicity of AT3.

The Toxic Effects of Pathogenic Ataxin-3 Variants in a Yeast Cellular Model

Ataxin-3 (AT3) is a deubiquitinating enzyme that triggers an inherited neurodegenerative disorder, spinocerebellar ataxia type 3, when its polyglutamine (polyQ) stretch close to the C-terminus exceeds a critical length. AT3 variants carrying the expanded polyQ are prone to associate with each other into amyloid toxic aggregates, which are responsible for neuronal death with ensuing neurodegeneration. We employed Saccharomyces cerevisiae as a eukaryotic cellular model to better clarify the mechanism by which AT3 triggers the disease. We expressed three variants: one normal (Q26), one expanded (Q85) and one truncated for a region lying from the beginning of its polyQ stretch to the end of the protein (291Δ). We found that the expression of the expanded form caused reduction in viability, accumulation of reactive oxygen species, imbalance of the antioxidant defense system and loss in cell membrane integrity, leading to necrotic death. The truncated variant also exerted a qualitatively similar, albeit milder, effect on cell growth and cytotoxicity, which points to the involvement of also non-polyQ regions in cytotoxicity. Guanidine hydrochloride, a well-known inhibitor of the chaperone Hsp104, almost completely restored wild-type survival rate of both 291Δ- and Q85-expressing strains. This suggests that AT3 aggregation and toxicity is mediated by prion forms of yeast proteins, as this chaperone plays a key role in their propagation.

Protein nanocages for self-triggered nuclear delivery of DNA-targeted chemotherapeutics in Cancer Cells

A genetically engineered apoferritin variant consisting of 24 heavy-chain subunits (HFn) was produced to achieve a cumulative delivery of an antitumor drug, which exerts its cytotoxic action by targeting the DNA at the nucleus of human cancer cells with subcellular precision. The rationale of our approach is based on exploiting the natural arsenal of defense of cancer cells to stimulate them to recruit large amounts of HFn nanoparticles loaded with doxorubicin inside their nucleus in response to a DNA damage, which leads to a programmed cell death. After demonstrating the selectivity of HFn for representative cancer cells compared to healthy fibroblasts, doxorubicin-loaded HFn was used to treat the cancer cells. The results from confocal microscopy and DNA damage assays proved that loading of doxorubicin in HFn nanoparticles increased the nuclear delivery of the drug, thus enhancing doxorubicin efficacy. Doxorubicin-loaded HFn acts as a "Trojan Horse": HFn was internalized in cancer cells faster and more efficiently compared to free doxorubicin, then promptly translocated into the nucleus following the DNA damage caused by the partial release in the cytoplasm of encapsulated doxorubicin. This self-triggered translocation mechanism allowed the drug to be directly released in the nuclear compartment, where it exerted its toxic action. This approach was reliable and straightforward providing an antiproliferative effect with high reproducibility. The particular self-assembling nature of HFn nanocage makes it a versatile and tunable nanovector for a broad range of molecules suitable both for detection and treatment of cancer cells.

Immobilization of carboxypeptidase from Sulfolobus solfataricus on magnetic nanoparticles improves enzyme stability and functionality in organic media

Background

Superparamagnetic iron oxide nanoparticles (MNP) offer several advantages for applications in biomedical and biotechnological research. In particular, MNP-based immobilization of enzymes allows high surface-to-volume ratio, good dispersibility, easy separation of enzymes from the reaction mixture, and reuse by applying an external magnetic field. In a biotechnological perspective, extremophilic enzymes hold great promise as they often can be used under non-conventional harsh conditions, which may result in substrate transformations that are not achievable with normal enzymes. This prompted us to investigate the effect of MNP bioconjugation on the catalytic properties of a thermostable carboxypeptidase from the hyperthermophilic archaeon Sulfolobus solfataricus (CPSso), which exhibits catalytic properties that are useful in synthetic processes.

Results

CPSso was immobilized onto silica-coated iron oxide nanoparticles via NiNTA-His tag site-directed conjugation. Following the immobilization, CPSso acquired distinctly higher long-term stability at room temperature compared to the free native enzyme, which, in contrast, underwent extensive inactivation after 72 h incubation, thus suggesting a potential utilization of this enzyme under low energy consumption. Moreover, CPSso conjugation also resulted in a significantly higher stability in organic solvents at 40°C, which made it possible to synthesize N-blocked amino acids in remarkably higher yields compared to those of free enzyme.

Conclusions

The nanobioconjugate of CPSso immobilized on silica-coated magnetic nanoparticles exhibited enhanced stability in aqueous media at room temperature as well as in different organic solvents. The improved stability in ethanol paves the way to possible applications of immobilized CPSso, in particular as a biocatalyst for the synthesis of N-blocked amino acids. Another potential application might be amino acid racemate resolution, a critical and expensive step in chemical synthesis.

Epigallocatechin-3-gallate and tetracycline differently affect ataxin-3 fibrillogenesis and reduce toxicity in spinocerebellar ataxia type 3 model

The polyglutamine (polyQ)-containing protein ataxin-3 (AT3) triggers the neurodegenerative disease spinocerebellar ataxia type 3 (SCA3) when its polyQ tract is expanded beyond a critical length. This results in protein aggregation and generation of toxic oligomers and fibrils. Currently, no effective treatment is available for such and other polyQ diseases. Therefore, plenty of investigations are being carried on to assess the mechanism of action and the therapeutic potential of anti-amyloid agents. The polyphenol compound epigallocatechin-3-gallate (EGCG) and tetracycline have been shown to exert some effect in preventing fibrillogenesis of amyloidogenic proteins. Here, we have incubated an expanded AT3 variant with either compound to assess their effects on the aggregation pattern. The process was monitored by atomic force microscopy and Fourier transform infrared spectroscopy. Whereas in the absence of any treatment, AT3 gives rise to amyloid β-rich fibrils, whose hallmark is the typical glutamine side-chain hydrogen bonding, when incubated in the presence of EGCG it generated soluble, SDS-resistant aggregates, much poorer in β-sheets and devoid of any ordered side-chain hydrogen bonding. These are off-pathway species that persist until the latest incubation time and are virtually absent in the control sample. In contrast, tetracycline did not produce major alterations in the structural features of the aggregated species compared with the control, but substantially increased their solubility. Both compounds significantly reduced toxicity, as shown by the MTT assay in COS-7 cell line and in a transgenic Caenorhabditis elegans strain expressing in the nervous system an AT3 expanded variant in fusion with GFP.

The Gravity Field and Interior Structure of Enceladus

The small and active Saturnian moon Enceladus is one of the primary targets of the Cassini mission. We determined the quadrupole gravity field of Enceladus and its hemispherical asymmetry using Doppler data from three spacecraft flybys. Our results indicate the presence of a negative mass anomaly in the south-polar region, largely compensated by a positive subsurface anomaly compatible with the presence of a regional subsurface sea at depths of 30 to 40 kilometers and extending up to south latitudes of about 50°. The estimated values for the largest quadrupole harmonic coefficients (106J2= 5435.2 ± 34.9, 106C22= 1549.8 ± 15.6, 1σ) and their ratio (J2/C22= 3.51 ± 0.05) indicate that the body deviates mildly from hydrostatic equilibrium. The moment of inertia is around 0.335MR2, whereMis the mass andRis the radius, suggesting a differentiated body with a low-density core.

Glucose-6-phosphate dehydrogenase deficiency in Italian blood donors: prevalence and molecular defect characterization

BACKGROUND

In the countries with high G6PD deficiency prevalence, blood donors are not routinely screened for this genetic defect. G6PD deficiency is often asymptomatic, blood donors may be carriers of the deficiency without being aware of it. The aim of the study was to evaluate the prevalence of G6PD deficiency among the Italian blood donors.

DESIGN AND METHODS

From October 2009 to April 2011, 3004 blood donors from a large hospital transfusion centre were screened for G6PD deficiency using differential pH-metry and the characterization of G6PD mutations was performed on G6PD-deficient subjects. The haematological features of G6PD-deficient and normal donors were also compared.

RESULTS

Thirty-three subjects (25 men and 8 women) with low G6PD activity were identified, corresponding to 1·1% of the examined blood donor population. The frequencies of class II severe alleles (Mediterranean, Valladolid, Chatham and Cassano) and class III mild alleles (Seattle, A- and Neapolis) were 48% and 43%, respectively. The haematological parameters of G6PD- donors were within normal range; however, the comparison between normal and G6PD- class II donors showed significant differences.

CONCLUSION

In Italy, the presence of blood donors with G6PD deficiency is not a rare event and the class II severe variants are frequent. The identification of G6PD-deficient donors and the characterization of the molecular variants would prevent the use of G6PD-deficient RBC units when the haemolytic complications could be relevant especially for high risk patients as premature infants and neonates and patients with sickle cell disease submitted to multiple transfusions.

A conserved loop in polynucleotide phosphorylase (PNPase) essential for both RNA and ADP/phosphate binding

Polynucleotide phosphorylase (PNPase) reversibly catalyzes RNA phosphorolysis and polymerization of nucleoside diphosphates. Its homotrimeric structure forms a central channel where RNA is accommodated. Each protomer core is formed by two paralogous RNase PH domains: PNPase1, whose function is largely unknown, hosts a conserved FFRR loop interacting with RNA, whereas PNPase2 bears the putative catalytic site, ∼20 Å away from the FFRR loop. To date, little is known regarding PNPase catalytic mechanism. We analyzed the kinetic properties of two Escherichia coli PNPase mutants in the FFRR loop (R79A and R80A), which exhibited a dramatic increase in Km for ADP/Pi binding, but not for poly(A), suggesting that the two residues may be essential for binding ADP and Pi. However, both mutants were severely impaired in shifting RNA electrophoretic mobility, implying that the two arginines contribute also to RNA binding. Additional interactions between RNA and other PNPase domains (such as KH and S1) may preserve the enzymatic activity in R79A and R80A mutants. Inspection of enzyme structure showed that PNPase has evolved a long-range acting hydrogen bonding network that connects the FFRR loop with the catalytic site via the F380 residue. This hypothesis was supported by mutation analysis. Phylogenetic analysis of PNPase domains and RNase PH suggests that such network is a unique feature of PNPase1 domain, which coevolved with the paralogous PNPase2 domain.

Hsp70 oligomerization is mediated by an interaction between the interdomain linker and the substrate-binding domain

Oligomerization in the heat shock protein (Hsp) 70 family has been extensively documented both in vitro and in vivo, although the mechanism, the identity of the specific protein regions involved and the physiological relevance of this process are still unclear. We have studied the oligomeric properties of a series of human Hsp70 variants by means of nanoelectrospray ionization mass spectrometry, optical spectroscopy and quantitative size exclusion chromatography. Our results show that Hsp70 oligomerization takes place through a specific interaction between the interdomain linker of one molecule and the substrate-binding domain of a different molecule, generating dimers and higher-order oligomers. We have found that substrate binding shifts the oligomerization equilibrium towards the accumulation of functional monomeric protein, probably by sequestering the helical lid sub-domain needed to stabilize the chaperone: substrate complex. Taken together, these findings suggest a possible role of chaperone oligomerization as a mechanism for regulating the availability of the active monomeric form of the chaperone and for the control of substrate binding and release.

A hydrophobic gold surface triggers misfolding and aggregation of the amyloidogenic Josephin domain in monomeric form, while leaving the oligomers unaffected

Protein misfolding and aggregation in intracellular and extracellular spaces is regarded as a main marker of the presence of degenerative disorders such as amyloidoses. To elucidate the mechanisms of protein misfolding, the interaction of proteins with inorganic surfaces is of particular relevance, since surfaces displaying different wettability properties may represent model systems of the cell membrane. Here, we unveil the role of surface hydrophobicity/hydrophilicity in the misfolding of the Josephin domain (JD), a globular-shaped domain of ataxin-3, the protein responsible for the spinocerebellar ataxia type 3. By means of a combined experimental and theoretical approach based on atomic force microscopy, Fourier transform infrared spectroscopy and molecular dynamics simulations, we reveal changes in JD morphology and secondary structure elicited by the interaction with the hydrophobic gold substrate, but not by the hydrophilic mica. Our results demonstrate that the interaction with the gold surface triggers misfolding of the JD when it is in native-like configuration, while no structural modification is observed after the protein has undergone oligomerization. This raises the possibility that biological membranes would be unable to affect amyloid oligomeric structures and toxicity.

Investigating the structural biofunctionality of antibodies conjugated to magnetic nanoparticles

We present the synthesis of trastuzumab-functionalized pegylated iron oxide nanoparticles and provide an FTIR-based approach to gain a direct evidence of the actual conservation of the native structure of conjugated antibody. Their target-selectivity to specific cancer cell receptors has been also assessed.

The mechanism of the polynucleotide phosphorylase-catalyzed arsenolysis of ADP

Using ADP and arsenate (AsV), polynucleotide phosphorylase (PNPase) catalyzes the apparent arsenolysis of ADP to AMP-arsenate and inorganic phosphate, with the former hydrolyzing rapidly into AMP and AsV. However, in the presence of glutathione, AMP-arsenate may also undergo reductive decomposition, yielding AMP and arsenite (AsIII). In order to clarify the mechanism of ADP arsenolysis mediated by Escherichia coli PNPase, we analyzed the time course of the reaction in the presence of increasing concentrations of ADP, with or without polyadenylate (poly-A) supplementation. These studies revealed that increasing supply of ADP enhanced the consumption of ADP but inhibited the production of both AMP and AsIII. Formation of these products was amplified by adding trace amount of poly-A. Furthermore, AMP and AsIII production accelerated with time, whereas ADP consumption slowed down. These observations collectively suggest that PNPase does not catalyze the arsenolysis of ADP directly (in a single step), but in two separate consecutive steps: the enzyme first converts ADP into poly-A, then it cleaves the newly synthesized poly-A by arsenolysis. It is inferred that one active site of PNPase can catalyze only one of these reactions at a time and that high ADP concentrations favor poly-A synthesis, thereby inhibiting the arsenolysis.

Single-domain protein A-engineered magnetic nanoparticles: toward a universal strategy to site-specific labeling of antibodies for targeted detection of tumor cells

Highly monodisperse magnetite nanocrystals (MNC) were synthesized in organic media and transferred to the water phase by ultrasound-assisted ligand exchange with an iminodiacetic phosphonate. The resulting biocompatible magnetic nanoparticles were characterized by transmission electron microscopy, dynamic light scattering, and magnetorelaxometry, indicating that this method allowed us to obtain stable particle dispersions with narrow size distribution and unusually high magnetic resonance T(2) contrast power. These nanoparticles were conjugated to a newly designed recombinant monodomain protein A variant, which exhibited a convincingly strong affinity for human and rabbit IgG molecules. Owing to the nature of antibody-protein A binding, tight antibody immobilization occurred through the Fc fragment thus taking full advantage of the targeting potential of bound IgGs. If necessary, monoclonal antibodies could be removed under controlled conditions regenerating the original IgG-conjugatable MNC. As a proof of concept of the utility of our paramagnetic labeling system of human IgGs for biomedical applications, anti-HER-2 monoclonal antibody trastuzumab was immobilized on hybrid MNC (TMNC). TMNC were assessed by immunoprecipitation assay and confocal microscopy effected on HER-2-overexpressing MCF-7 breast cancer cells, demonstrating excellent recognition capability and selectivity for the target membrane receptor.

Polynucleotide phosphorylase and mitochondrial ATP synthase mediate reduction of arsenate to the more toxic arsenite by forming arsenylated analogues of ADP and ATP

We have demonstrated that phosphorolytic-arsenolytic enzymes can promote reduction of arsenate (AsV) into the more toxic arsenite (AsIII) because they convert AsV into an arsenylated product in which the arsenic is more reducible by glutathione (GSH) or other thiols to AsIII than in inorganic AsV. We have also shown that mitochondria can rapidly reduce AsV in a process requiring intact oxidative phosphorylation and intramitochondrial GSH. Thus, these organelles might reduce AsV because mitochondrial ATP synthase, using AsV instead of phosphate, arsenylates ADP to ADP-AsV, which in turn is readily reduced by GSH. To test this hypothesis, we first examined whether the RNA-cleaving enzyme polynucleotide phosphorylase (PNPase), which can split poly-adenylate (poly-A) by arsenolysis into units of AMP-AsV (a homologue of ADP-AsV), could also promote reduction of AsV to AsIII in presence of thiols. Indeed, bacterial PNPase markedly facilitated formation of AsIII when incubated with poly-A, AsV, and GSH. PNPase-mediated AsV reduction depended on arsenolysis of poly-A and presence of a thiol. PNPase can also form AMP-AsV from ADP and AsV (termed arsenolysis of ADP). In presence of GSH, this reaction also facilitated AsV reduction in proportion to AMP-AsV production. Although various thiols did not influence the arsenolytic yield of AMP-AsV, they differentially promoted the PNPase-mediated reduction of AsV, with GSH being the most effective. Circumstantial evidence indicated that AMP-AsV formed by PNPase is more reducible to AsIII by GSH than inorganic AsV. Then, we demonstrated that AsV reduction by isolated mitochondria was markedly inhibited by an ADP analogue that enters mitochondria but is not phosphorylated or arsenylated. Furthermore, inhibitors of the export of ATP or ADP-AsV from the mitochondria diminished the increment in AsV reduction caused by adding GSH externally to these organelles whose intramitochondrial GSH had been depleted. Thus, whereas PNPase promotes reduction of AsV by incorporating it into AMP-AsV, the mitochondrial ATP synthase facilitates AsV reduction by forming ADP-AsV; then GSH can easily reduce these arsenylated nucleotides to AsIII.

Proteomic and biochemical analyses unveil tight interaction of ataxin-3 with tubulin

Ataxin-3 consists of an N-terminal globular Josephin domain and an unstructured C-terminal region containing a stretch of consecutive glutamines that triggers an inherited neurodegenerative disorder, spinocerebellar ataxia type 3, when its length exceeds a critical threshold. The pathology results from protein misfolding and intracellular accumulation of fibrillar amyloid-like aggregates. Plenty of work has been carried out to elucidate the protein's physiological role(s), which has shown that ataxin-3 is multifunctional; it acts as a transcriptional repressor, and also has polyubiquitin-binding/ubiquitin-hydrolase activity. In addition, a recent report shows that it participates in sorting misfolded protein to aggresomes, close to the microtubule-organizing center. Since a thorough understanding of the protein's physiological role(s) requires the identification of all the molecular partners interacting with ataxin-3, we pursued this goal by taking advantage of two-dimensional chromatography coupled to tandem mass spectrometry. We found that different ataxin-3 constructs, including the sole Josephin domain, bound alpha- and beta-tubulin from soluble rat brain extracts. Coimmunoprecipitation experiments confirmed this interaction. Also, normal ataxin-3 overexpressed in COS7 cultured cells partially colocalized with microtubules, whereas an expanded variant only occasionally did so, probably due to aggregation. Furthermore, by surface plasmon resonance we determined a dissociation constant of 50-70nM between ataxin-3 and tubulin dimer, which strongly supports the hypothesis of a direct interaction of this protein with microtubules in vivo. These findings suggest an involvement of ataxin-3 in directing aggregated protein to aggresomes, and shed light on the mode of interaction among the different molecular partners participating in the process.

A combined approach of mass spectrometry, molecular modeling, and site-directed mutagenesis highlights key structural features responsible for the thermostability of Sulfolobus solfataricus carboxypeptidase

Sulfolobus solfataricus carboxypeptidase (CPSso) is a thermostable zinc-metalloenzyme, consisting of four identical subunits with a M(r) of 43,000. In a previous paper (Occhipinti et al., Biophys J 2003; 85:1165-1175), we developed a structure of the enzyme by molecular modeling and validated it by site-directed mutagenesis and small angle X-ray scattering. Here, we report investigations aimed at further validating the model, as well as at identifying molecular determinants responsible for thermostability. To this end, we took advantage of mass spectrometry techniques, notably LC-MS/MS. The structure was confirmed by such approaches, in that they lead to the identification of a disulfide bridge formed by Cys286 and Cys293, whose location in the model is well suited for giving rise to the crosslink. More notably, we also identified a protease-resistant core consisting of the N- and C-terminal antiparallel alpha-helices, which in the model are predicted to interact with each other via hydrophobic quadrants. On the basis of the model, we also tentatively identified the most tightly interacting residues as Leu7, Ala380, and Leu376. Although the replacement of Ala380 by serine did not detectably impair protein stability, a dramatic drop in thermostability was observed when the two leucines were replaced by either aspartate (L7D; L376D) or asparagine (L7N; L376N). We then investigated the kinetic thermal stability of the wild type and the mutants by determining the thermodynamic activation parameters, DeltaG++, DeltaH++, and DeltaS++. Besides highlighting the key role of the hydrophobic core in thermostability, these results suggest clearly different mechanisms of destabilization by the single mutations, depending on whether the leucines are replaced by asparagines or aspartates.

Regulation of Escherichia coli polynucleotide phosphorylase by ATP

Polynucleotide phosphorylase (PNPase), an enzyme conserved in bacteria and eukaryotic organelles, processively catalyzes the phosphorolysis of RNA, releasing nucleotide diphosphates, and the reverse polymerization reaction. In Escherichia coli, both reactions are implicated in RNA decay, as addition of either poly(A) or heteropolymeric tails targets RNA to degradation. PNPase may also be associated with the RNA degradosome, a heteromultimeric protein machine that can degrade highly structured RNA. Here, we report that ATP binds to PNPase and allosterically inhibits both its phosphorolytic and polymerization activities. Our data suggest that PNPase-dependent RNA tailing and degradation occur mainly at low ATP concentrations, whereas other enzymes may play a more significant role at high energy charge. These findings connect RNA turnover with the energy charge of the cell and highlight unforeseen metabolic roles of PNPase.

Hyperion's sponge-like appearance

Hyperion is Saturn's largest known irregularly shaped satellite and the only moon observed to undergo chaotic rotation. Previous work has identified Hyperion's surface as distinct from other small icy objects but left the causes unsettled. Here we report high-resolution images that reveal a unique sponge-like appearance at scales of a few kilometres. Mapping shows a high surface density of relatively well-preserved craters two to ten kilometres across. We have also determined Hyperion's size and mass, and calculated the mean density as 544 +/- 50 kg m(-3), which indicates a porosity of >40 per cent. The high porosity may enhance preservation of craters by minimizing the amount of ejecta produced or retained, and accordingly may be the crucial factor in crafting this unusual surface.

Avidin Decorated Core–Shell Nanoparticles for Biorecognition Studies by Elastic Light Scattering

In this paper, a straightforward method based on elastic light scattering is shown to provide a sensitive and reliable tool for the quantitative determination of protein-ligand interactions that occur at the surface of suitably designed core-shell nanoparticles. The assay makes use of monodisperse nanocolloids that have minimal optical contrast with the aqueous environment. By properly coating the particles with avidin and oligo(ethylene glycol)-based amphiphiles, we developed a hybrid system that combines the availability of standard ligands with the necessary bioinvisibility towards the accidental adsorption of nonspecific macromolecules. This probe was employed to detect interactions between different kinds of biotinylated proteins, and it revealed high specificity and affinities in the low nanomolar range. In particular, we obtained an efficient avidin anchorage of biotinylated protein A on the surface of the nanoparticles, which we exploited as a functional probe for the rapid, quantitative, picomolar detection of human IgG antibodies. Overall, these light-scattering-based nanosensors appear as a simple and highly informative tool for proteomics studies.

The KH and S1 domains of Escherichia coli polynucleotide phosphorylase are necessary for autoregulation and growth at low temperature

PNPase is a phosphate-dependent exonuclease of Escherichia coli required for growth in the cold. In this work we explored the effect of specific mutations in its two RNA binding domains KH and S1 on RNA binding, enzymatic activities, autoregulation and ability to grow at low temperature. We removed critical motifs that stabilize the hydrophobic core of each domain, as well as made a complete deletion of both (DeltaKHS1) that severely impaired PNPase binding to RNA. Nevertheless, a residual RNA binding activity, possibly imputable to catalytic binding, could be observed even in the DeltaKHS1 PNPase. These mutations also resulted in significant changes in the kinetic behavior of both phosphorolysis and polymerization activities of the enzyme, in particular for the double mutant Pnp-DeltaKHS1-H. Additionally, PNPases with mutations in these RNA binding domains did not autoregulate efficiently and were unable to complement the growth defect of a chromosomal Deltapnp mutation at 18 degrees C. Based on these results it appears that in E. coli the RNA binding domains of PNPase, in particular the KH domain, are vital at low temperature, when the stem-loop structures present in the target mRNAs are more stable and a machinery capable to degrade structured RNA may be essential.

Destabilization of non-pathological variants of ataxin-3 by metal ions results in aggregation/fibrillogenesis

Ataxin-3 (AT3), a protein that causes spinocerebellar ataxia type 3, has a C-terminus containing a polyglutamine stretch, the length of which can be expanded in its pathological variants. Here, we report on the role of Cu(2+), Mn(2+), Zn(2+) and Al(3+) in the induction of defective protein structures and subsequent aggregation/fibrillogenesis of three different non-pathological forms of AT3, i.e. murine (Q6), human non-expanded (Q26) and human moderately expanded (Q36). AT3 variants showed an intrinsic propensity to misfolding/aggregation; on the other hand, Zn(2+) and Al(3+) strongly stimulated the amplitude and kinetics of these conformational conversions. While both metal ions induced a time-dependent aggregation into amyloid-like fibrillar forms, only small oligomers and/or short protofibrillar species were detected for AT3s alone. The rate and extent of the metal-induced aggregation/fibrillogenesis processes increased with the size of the polyglutamine stretch. Mn(2+) and Cu(2+) had no effect on (Q6) or actually prevented (Q26 and Q36) the AT3 structural transitions. The observation that Zn(2+) and Al(3+) promote AT3 fibrillogenesis is consistent with similar results found for other amyloidogenic molecules, such as beta-amyloid and prion proteins. Plausibly, these metal ions are a major common factor/cofactor in the etiopathogenesis of neurodegenerative diseases. Studies of liposomes as membrane models showed dramatic changes in the structural properties of the lipid bilayer in the presence of AT3, which were enhanced after supplementing the protein with Zn(2+) and Al(3+). This suggests that cell membranes could be a potential primary target in the ataxin-3 pathogenesis and metals could be a biological factor capable of modulating their interaction with AT3.