Structural Lability Research Articles

Designer phospholipid capping ligands for soft metal halide nanocrystals

The success of colloidal semiconductor nanocrystals (NCs) in science and optoelectronics is inextricable from their surfaces. The functionalization of lead halide perovskite NCs1–5 poses a formidable challenge because of their structural lability, unlike the well-established covalent ligand capping of conventional semiconductor NCs6,7. We posited that the vast and facile molecular engineering of phospholipids as zwitterionic surfactants can deliver highly customized surface chemistries for metal halide NCs. Molecular dynamics simulations implied that ligand–NC surface affinity is primarily governed by the structure of the zwitterionic head group, particularly by the geometric fitness of the anionic and cationic moieties into the surface lattice sites, as corroborated by the nuclear magnetic resonance and Fourier-transform infrared spectroscopy data. Lattice-matched primary-ammonium phospholipids enhance the structural and colloidal integrity of hybrid organic–inorganic lead halide perovskites (FAPbBr3 and MAPbBr3 (FA, formamidinium; MA, methylammonium)) and lead-free metal halide NCs. The molecular structure of the organic ligand tail governs the long-term colloidal stability and compatibility with solvents of diverse polarity, from hydrocarbons to acetone and alcohols. These NCs exhibit photoluminescence quantum yield of more than 96% in solution and solids and minimal photoluminescence intermittency at the single particle level with an average ON fraction as high as 94%, as well as bright and high-purity (about 95%) single-photon emission.

NMR-Verified Dearomatization of 5,7-Substituted Pyrazolo[1,5-a]pyrimidines.

Tetrahydropyrazolo[1,5-a]pyrimidine (THPP) is an attractive scaffold for designing biologically active compounds. The most obvious way to obtain such compounds is to reduce pyrazolopyrimidines with complex hydrides, because the pyrimidine ring is reduced in the preference over the pyrazole ring. The presence of substituents at positions five and seven of pyrazolo[1,5-a]pyrimidines complicates the set of reaction products but makes it more attractive for medicinal chemistry because four possible stereoisomers can be formed during reduction. However, the formation of only syn-isomers has been described in the literature. This article is the first report on the formation of anti-configured isomers along with syn-isomers in the reduction of model 5,7-dimethylpyrazolo[1,5-a]pyrimidine, which was confirmed by NMR. The bicyclic core in the syn-configuration was shown to be conformationally stable, which was used to estimate the long-range interproton distances using NOESY data. At the same time, long-range dipole-dipole interactions corresponding to a distance between protons of more than 6 Å were first registered and quantified. In turn, the bicyclic core in the trans-configuration represents a conformationally labile system. For these structures, an analysis of conformations observed in solutions was carried out. Our results indicate the significant potential of trans-configured tetrahydropyrazolo[1,5-a]pyrimidines for the development of active small molecules. While possessing structural lability due to the low energy of the conformational transition, they have the ability to adjust to the active site of the desired target.

Constructing Ultrastable Metallo-Cages via In Situ Deprotonation/Oxidation of Dynamic Supramolecular Assemblies.

Coordination-driven self-assembly enables the spontaneous construction of metallo-supramolecules with high precision, facilitated by dynamic and reversible metal-ligand interactions. The dynamic nature of coordination, however, results in structural lability in many metallo-supramolecular assembly systems. Consequently, it remains a formidable challenge to achieve self-assembly reversibility and structural stability simultaneously in metallo-supramolecular systems. To tackle this issue, herein, we incorporate an acid-/base-responsive tridentate ligand into multitopic building blocks to precisely construct a series of metallo-supramolecular cages through coordination-driven self-assembly. These dynamic cagelike assemblies can be transformed to their static states through mild in situ deprotonation/oxidation, leading to ultrastable skeletons that can withstand high temperatures, metal ion chelators, and strong acid/base conditions. This in situ transformation provides a reliable and powerful approach to manipulate the kinetic features and stability of metallo-supramolecules and allows for modulation of encapsulation and release behaviors of metallo-cages when utilizing nanoscale quantum dots (QDs) as guest molecules.

Stable perovskite single-crystal X-ray imaging detectors with single-photon sensitivity

A major thrust of medical X-ray imaging is to minimize the X-ray dose acquired by the patient, down to single-photon sensitivity. Such characteristics have been demonstrated with only a few direct-detection semiconductor materials such as CdTe and Si; nonetheless, their industrial deployment in medical diagnostics is still impeded by elaborate and costly fabrication processes. Hybrid lead halide perovskites can be a viable alternative owing to their facile solution growth. However, hybrid perovskites are unstable under high-field biasing in X-ray detectors, owing to structural lability and mixed electronic–ionic conductivity. Here we show that both single-photon-counting and long-term stable performance of perovskite X-ray detectors are attained in the photovoltaic mode of operation at zero-voltage bias, employing thick and uniform methylammonium lead iodide single-crystal films (up to 300 µm) and solution directly grown on hole-transporting electrodes. The operational device stability exceeded one year. Detection efficiency of 88% and noise-equivalent dose of 90 pGyair are obtained with 18 keV X-rays, allowing single-photon-sensitive, low-dose and energy-resolved X-ray imaging. Array detectors demonstrate high spatial resolution up to 11 lp mm−1. These findings pave the path for the implementation of hybrid perovskites in low-cost, low-dose commercial detector arrays for X-ray imaging.

Self-assembly of smooth muscle myosin filaments: adaptation of filament length by telokin and Mg·ATP.

The contractile apparatus of smooth muscle is malleable to accommodate stress and strain exerted on the muscle cell and to maintain optimal contractility. Structural lability of smooth muscle myosin filaments is believed to play an important role in the cell's malleability. However, the mechanism and regulation of myosin filament formation is still poorly understood. In the present in vitro study, using a static light scattering method, length distributions were obtained from suspensions of short myosin filaments (SFs) formed by rapid dilution or long ones (LFs) formed by slow dialysis. The distributions indicated the presence of dynamic equilibriums between soluble myosin and the SFs; i.e.: trimers, hexamers and mini filaments, covering the range up to 0.75µm. The LFs were more stable, exhibiting favorable sizes at about 1.25, 2.4 and 4.5µm. More distinct distributions were obtained from filaments adsorbed to a glass surface, by evanescent wave scattering and local electric field enhancement. Addition of telokin (TL) to the suspensions of unphosphorylated SFs resulted in widening of the soluble range, while in the case of the LFs this shift was larger, and accompanied by reduced contribution of the soluble myosin species. Such changes were largely absent in the case of phosphorylated myosin. In contrast, the presence of Mg·ATP resulted in elongation of the filaments and clear separation of filaments from soluble myosin species. Thus, TL and Mg·ATP appeared to modify the distribution of myosin filament lengths, i.e., increasing the lengths in preparing for phosphorylation, or reducing it to aid dephosphorylation.

Enhancing the anti-psoriatic activity of vitamin D3 employing nanostructured archaeolipid carriers

Psoriasis (Ps) is a multifactorial autoimmune skin disease, where oxidative stress plays a key role in promoting a vicious producing cycle between keratinocytes and immune cells. Vitamin D3 (VD3) regulates the differentiation, apoptosis, and proliferation of keratinocytes, also displaying antioxidant and anti-inflammatory activities. Previous attempts of using topical VD3 as anti-psoriatic agent, failed because of its poor solubility, high hydrophobicity, structural lability, and low bioavailability. Specifically tailored nanoparticles for topical co-delivery of VD3 and antioxidants to activated keratinocytes and macrophages could make Ps treatments more efficient. In this work, structural features, and in vitro activity of nanostructured archaeolipid carriers (NAC) containing VD3 plus the antioxidant C50 dipolar carotenoid bacterioruberin (BR) (NAC-VD3), are presented. Ultra-small (70 nm), −39 mV ζ potential, ∼5 mg VD3/ml, 0.35 BR μg/ml NAC-VD3, with good storage stability (at least 6 month) consisted of a compritol and BR core, covered by a shell of sn 2,3 ether linked archaeolipids and Tween 80 (2: 2: 1.2: 3% w/w) were obtained. Raman, DSC and SAXS analysis showed that VD3 was trapped within the disordered compritol-BR core, impairing its fast release, and protecting VD3 against thermal degradation. NAC-VD3 were extensively captured and displayed high anti-proliferative (65%), anti-inflammatory (IL-8 release) and antioxidant activities (ROS reduction) on a psoriatic model made of CaCl2 differentiated-imiquimod stimulated HaCaT cells, and on lipopolysaccharide induced THP-1 macrophages. Interestingly, the BR extract alone displayed high anti-Staphylococcus aureus activity including anti-biofilm formation. Overall, the results suggest that NAC-VD3 protect the labile structure of VD3, while enhancing its anti-psoriatic activity and deserves further in vivo exploration.

Design of Promising aza-BODIPYs for Bioimaging and Sensing

The obtainment of new luminophores for molecular sensorics of biosystems is becoming one of the urgent tasks in the field of chemical synthesis. The solution to each practical problem imposes its own limitations in the design of new structures with practically useful properties. The relationship between the structure and spectral properties is still to be unveiled. Three aza-BODIPY complexes with substituents of different natures were studied using time-resolved and steady-state fluorescence and absorption spectroscopy. The solvatochromic properties of aza-BODIPYs were studied with the use of a combined polyparametric approach and analysis by chemoinformatics methods for the first time. It was found that red shift of aza-BODIPY dyes was due to the increase of their structural lability. Predictive and experimental methods showed that the investigated aza-BODIPYs exhibited a positive solvatochromic effect, in contrast to classic BODIPYs (bearing C in the meso-position of the dipyrromethene core), which represents the negative solvatochromic properties. Spectral maxima in the area of the therapeutic window, low and predictable solvatochromism, and the ability to fine-tune the spectral characteristics make the investigated aza-BODIPYs promising scaffolds for the construction of bioengineering devices. Generalizations on the aza-BODIPYs’ design patterns were made in accordance with further bioimaging applications.

Reparation of an Inflamed Air-Liquid Interface Cultured A549 Cells with Nebulized Nanocurcumin.

The anti-inflammatory, antifibrotic and antimicrobial activities of curcumin (CUR) are missed because of its low solubility in aqueous media, low bioavailability, and structural lability upon oral intake. Soft nanoparticles such as nanoliposomes are not efficient as CUR carriers, since crystalline CUR is expelled from them to physiological media. Nanostructures to efficiently trap and increase the aqueous solubility of CUR are needed to improve both oral or nebulized delivery of CUR. Here we showed that SRA1 targeted nanoarchaeosomes (nATC) [1:0.4 w:w:0.04] archaeolipids, tween 80 and CUR, 155 ± 16 nm sized of −20.7 ± 3.3 z potential, retained 0.22 mg CUR ± 0.09 per 12.9 mg lipids ± 4.0 (~600 μM CUR) in front to dilution, storage, and nebulization. Raman and fluorescence spectra and SAXS patterns were compatible with a mixture of enol and keto CUR tautomers trapped within the depths of nATC bilayer. Between 20 and 5 µg CUR/mL, nATC was endocytosed by THP1 and A549 liquid–liquid monolayers without noticeable cytotoxicity. Five micrograms of CUR/mL nATC nebulized on an inflamed air–liquid interface of A549 cells increased TEER, normalized the permeation of LY, and decreased il6, tnfα, and il8 levels. Overall, these results suggest the modified pharmacodynamics of CUR in nATC is useful for epithelia repair upon inflammatory damage, deserving further deeper exploration, particularly related to its targeting ability.

Water-Triggered Transformation of Ligand-Free Lead Halide Perovskite Nanocrystal-Embedded Pb(OH)Br with Ultrahigh Stability.

Lead halide perovskite (LHP) nanomaterials have attracted tremendous attention owing to their remarkable optoelectronic properties. However, they are extremely unstable under moist environments, high temperatures, and light illumination due to their intrinsic structural lability, which has been the critical unsolved problem for practical applications. To address this issue, we propose a facile and environmentally friendly ligand-free approach to design and synthesize rod-like CsPb2Br5-embedded Pb(OH)Br with excellent stability under various harsh environments such as soaking in water, heating, and ultraviolet (UV) illumination. Plate-like CsPbBr3- and Cs4PbBr6-embedded Pb(OH)Br powders are first formed by evaporating the solvent in a dispersion of ethanol (or methanol, isopropanol), Cs2CO3, and PbBr2. Upon soaking in water, the plate-like sample undergoes phase transformation from CsPbBr3 and Cs4PbBr6 to CsPb2Br5 and shape conversion from nanoplate to a microrod, leading to the formation of rod-like CsPb2Br5-embedded Pb(OH)Br. The stable Pb(OH)Br coating effectively prevents the luminescent CsPb2Br5 nanocrystals from reacting with water, leading to extremely high aqueous stability of the CsPb2Br5-embedded Pb(OH)Br. The photoluminescence (PL) intensity of the representative CsPb2Br5-embedded Pb(OH)Br sample can maintain 92.2% of the initial PL intensity value even after soaking in room-temperature water for 165 days; in the meantime, the phase and shape are preserved. The typical sample also shows outstanding stability under hot water, UV illumination, and annealing conditions. The ultrahigh aqueous stability, thermal stability, and photostability of the CsPb2Br5-embedded Pb(OH)Br nanomaterials suggest an effective, facile, and environmentally friendly technique to grow perovskite-based nanomaterials for promising practical applications in the optoelectronic field.

Modulation of Metal Halide Structural Units for Light Emission.

ConspectusWith the development of solid-state lighting technology, efficient light sources that combine high brightness, wide range, and good stability are in high demand for next-generation lighting and displays. Metal halides are emerging as promising luminescent materials due to their versatility for desirable light emission manipulations. This is because the optical activity of the metal halide material depends on the metal halide structural unit and the organic ions or coordinated organic ligands. The different assembly of metal halide units and organic parts can enable versatile light emissions, such as lead halide perovskites (LHPs) and copper halide-organic hybrids. Impressively, the external quantum efficiency of the LHP based light-emitting diodes (LEDs) has improved significantly from 0.1% to over 20% in just five years. With this great progress, the structural lability and toxicity of the LHPs are now the critical issues that need to be addressed for practical applications. These issues are mainly rooted in the intrinsic lead composition and low formation energy crystal structure of the widely adopted LHPs. Thus, the modulation of the structure and composition of the basic metal halide structural units is considered a rational strategy to address these issues.In this Account, we will present a general material design using metal halide structural units as basic building blocks to build up metal halide luminescent materials for solid-state lighting devices. Following this route, we will emphasize the modulation of metal halide structural units to tackle the existing challenges in lead halides, including the instability of crystalline structure, ion migration, and the presence of toxic lead. Considering basic components in structural units, we will highlight ionic engineering in LHPs via ion doping, substitution, and modification to enhance the crystal structural stability and suppress ion migration. To replace toxic lead, we will introduce recent advances in the modulation of lead-free halide structural units by active ion doping and organic ligand coordination to fabricate highly luminescent materials. Finally, we will present future strategies of metal halide structural unit modulation for solid-state light emissions. We hope this Account will provide new insights for designing metal halide materials from the viewpoint of the modulation of the basic building blocks and inspire future studies of advanced metal halide materials for solid-state light emitting applications.

Управління структурними трансформаціями у старопромислових регіонах України: концепт державної політики

The concept of public policy of structural transformations in old-industrial regions of Ukraine has been grounded. The necessity to separate old-industrial region as an object of public regional policy has been proven, as well as to manage structural changes with the obligatory orientation on the principles of “new regionalism”. This grounding is based on the studies of historical and economic prerequisites of old-industrial regions’ emergence in the world and in Ukraine; on the theoretical generalization of the essence of a category “old-industrial region”, clarification of the characteristics of old-industrial regions, specifying its properties, generated by the regularities of long-time development of these regions at the industrial basis; on the critical generalization of world experience of structural reconstruction old-industrial regions, rethinking this process based on practical faults’ analysis, finding out its causes and evolution of approaches to economic structure of the regions improvement; on the determination of specific features of old-industrial regions (structural and social inertia, endogenous depressiveness, low adapting capacity, low inclusiveness of development) as structure-creating determinants, that set general and specific imperatives of overcoming structural contradictions of its economic development (diversification, smart-specialization, restructuring of “basic” industries of economy of the regions); on finding out of the basic features of post-transformation model of the economy of old-industrial regions of Ukraine – the “post-industrial synthesis” model – as the result of structural changes in its economy. The implementation of the model is indicated by the formation of a number of substantial features (structural lability, social initiative and adaptiveness, territorial cohesion and economic inclusiveness, capacity to endogenous growth).

Functional outcomes of structural peculiarities of striated muscle tropomyosin.

Tropomyosin is a dimer coiled-coil actin-binding protein. Adjacent tropomyosin molecules connect each other 'head-to-tail' via an overlap junction and form a continuous strand that winds around an actin filament and controls the actin-myosin interaction. High cooperativity of muscle contraction largely depends on tropomyosin characteristics. Here we summarise experimental evidence that local peculiarities of tropomyosin structure have long-range effects and determine functional properties of the strand, including changes in its bending stiffness and interaction with actin and myosin. Point mutations and posttranslational modifications help to probe the roles of the conserved 'non-canonical' residues, clusters of stabilising and destabilising core residues, and core gap in tropomyosin function. The data suggest that tropomyosin structural lability including a diversity of homo- and heterodimers of different isoforms provide a balance of stiffness, flexibility, and strength of interaction with partner sarcomere proteins necessary for fine-tuning of Ca2+ regulation in various types of striated muscles.

Ultrastable Carbon Quantum Dots-Doped MAPbBr3 Perovskite with Silica Encapsulation.

Having suffered from intrinsic structural lability, perovskite quantum dots (PQDs) are extremely unstable under high-temperature and moisture conditions, which have greatly limited their applications. In this work, we propose a novel method to synthesize ultrastable carbon quantum dots (CQDs)-doped methylamine (MA) lead bromide PQDs with SiO2 encapsulation (CQDs-MAPbBr3@SiO2). The kernel CQDs-MAPbBr3 is formed by the interaction of carboxyl-rich CQDs with MAPbBr3 via H-bond, which greatly improves the thermal stability of CQDs-MAPbBr3. Furthermore, highly compact SiO2 encapsulates the proposed CQDs-MAPbBr3 via a facile in situ growth strategy, which effectively enhances the water resistance and air stability of CQDs-MAPbBr3@SiO2. As a result, the proposed nanomaterial shows extremely high water stability in aqueous solution for over 9 months and ideal thermal stability with strong fluorescence (FL) emission after 150 °C annealing. Based on the superior stability and ultrahigh FL efficiency of this proposed nanomaterial, a primary sensing method for ion (Ag+ and Zn2+) FL detection has been developed and the mechanism of PQDs-based ion determination has also been discussed, thus exhibiting the potential applications of CQDs-MAPbBr3@SiO2 in the area of FL assay and environment monitoring.

Thermosensitive Nanogels with Cross-Linked Pd(II) Ions for Improving Therapeutic Effects on Platinum-Resistant Cancers via Intratumoral Formation of Hydrogels

Although bivalent palladium [Pd(II)] compounds exhibit favorable antitumor efficacy against platinum-resistant cancers, the mechanism remains unclear. Moreover, some drawbacks, such as structural lability, rapid elimination in vivo, and poor intratumoral retention, heavily limit their application in systemic tumor chemotherapy. Here, thermosensitive Pd-PNS nanogels are rationally designed by cross-linking coordination of Pd(II) ions with poly(styrenesulfonate-b-N-isopropylacrylamide-b-styrenesulfonate) (PNS), achieving high drug-loading ability (ca. 80% of entrapment efficiency and 40% of drug-loading efficiency), sustained release, and long-term retention of highly water-soluble K2PdCl4 in intratumoral administration. Cytotoxicity on sensitive/resistant MCF-7 cells and cancer stem cell (CSC) spheroids indicates that Pd-PNS nanogels could inhibit the palladium efflux of P-glycoprotein and multidrug resistance-associated protein-1 and thus enhance the DNA damage and toxicity of platinum-resistant MCF-7/Pt cells and their CSCs. Based on their temperature-sensitive sol–gel transition, Pd-PNS nanogels show sustained release profiles and long-term retention in tumors, further enhancing in vivo antitumor efficacy on MCF-7/Pt tumor-bearing BALB/c nude mice. Owing to these advantages of prolonged retention, efflux inhibition, and efficient CSCs killing ability, Pd-PNS nanogels are promising to be developed as a new temperature-sensitive delivery nanoplatform for injectable regional chemotherapy on platinum-resistant cancers.

Aqueous stable luminescent perovskite-polymer composites

The applicability of lead halide perovskites nanocrystals (LHP NCs) is limited by their structural lability in aqueous media or under high humidity levels. One of the most straightforward solutions is their entrapment in glass or salt matrixes. Here, we propose the use of the amphiphilic polymer poly-(isobutylene-alt-maleic anhydride)-graft-dodecyl (PMA), which has been widely used to provide nanoparticles with colloidal stability in aqueous media. The partial hydrolysis of the polymeric matrix allows the LHP NCs to maintain their photoluminescence properties for extended periods of time (months), both in solution and upon surface deposition. Moreover, the PMA-glass formation prevents anionic exchange processes in LHP NCs and increases their thermal stability in aqueous solution. Importantly, the inclusion of fluorophores covalently bonded to the polymer matrix allows for fluorophore-activation by the LHP NCs through energy transfer triggered by near-IR excitation.

Umbelliferone instability during an analysis involving its extraction process

Umbelliferone (7-hydroxycoumarin) is one of the most popular compounds of the coumarins family. This compound receives the attention of scientists due to its diverse bioactivities in a number of applications in various therapeutic fields. An interesting aspect of umbelliferone is its structural lability. The enzymatic degradation process of umbelliferone to its hydroxylated (esculetin), glucosylated (skimmin), and methylated (herniarin) derivatives is already known from the literature. In this paper, we describe the possibility of umbelliferone transformation to other derivatives. We found that eight compounds were formed from umbelliferone during its simulated extraction under reflux performed in different conditions (different heating times and solvents used). Six of them (4,7-dihydroxy-3,4-dihydro-2H-chromen-2-one, 3,7-dihydroxy-3,4-dihydro-2H-chromen-2-one, methyl (2E)-3-(2,4-dihydroxyphenyl)prop-2-enoate, ethyl (2E)-3-(2,4-dihydroxyphenyl)prop-2-enoate, (2E)-3-[2-(acetyloxy)-4-hydroxyphenyl]prop-2-enoic acid, (2E)-3-(2-amino-4-hydroxyphenyl)prop-2-enoic acid) have not been reported yet. Some of these compounds were also identified in extracts of plant materials containing umbelliferone—chamomile flower and cinnamon bark. Compound separation was carried out using the HPLC apparatus. All compounds were identified based on their MS fragmentation paths. The presented results are useful for food producers and consumers, as umbelliferone transformation products can be formed during food product storage, their preparation or processing.Graphical abstract

The Solution Structure of CCL28 Reveals Structural Lability that Does Not Constrain Antifungal Activity

The chemokine CCL28 is constitutively expressed in mucosal tissues and is abundant in low-salt mucosal secretions. Beyond its traditional role as a chemoattractant, CCL28 has been shown to act as a potent and broad-spectrum antimicrobial agent with particular efficacy against the commensal fungus and opportunistic pathogen Candida albicans. However, the structural features that allow CCL28 to perform its chemotactic and antimicrobial functions remain unknown. Here, we report the structure of CCL28, solved using nuclear magnetic resonance spectroscopy. CCL28 adopts the canonical chemokine tertiary fold, but also has a disordered C-terminal domain that is partially tethered to the core by a non-conserved disulfide bond. Structure–function analysis reveals that removal of the C-terminal tail reduces the antifungal activity of CCL28 without disrupting its structural integrity. Conversely, removal of the non-conserved disulfide bond destabilizes the tertiary fold of CCL28 without altering its antifungal effects. Moreover, we report that CCL28 unfolds in response to low pH but is stabilized by the presence of salt. To explore the physiologic relevance of the observed structural lability of CCL28, we investigated the effects of pH and salt on the antifungal activity of CCL28 in vitro. We found that low pH enhances the antifungal potency of CCL28, but also that this pH effect is independent of CCL28's tertiary fold. Given its dual role as a chemoattractant and antimicrobial agent, our results suggest that changes in the salt concentration or pH at mucosal sites may fine-tune CCL28's functional repertoire by adjusting the thermostability of its structure.

Is MHCII-restricted immunodominance determined by HLA-DM action?

Abstract Binding of antigenic peptides to class II MHC molecules (MHCII) and the activity of the “editing” molecule HLA-DM (DM) on the resulting peptide-MHCII complexes are mechanisms critical to immunodominance, yet not fully understood. Our previous results indicate that peptide binding to the human MHCII HLA-DR1 (DR1) is a flexible event in that different thermodynamic components compensate each other to the possible extent to achieve a stable complex, and the energetic mechanism responsible for binding is reflected in the structural lability of the resulting complex. Here we apply our thermodynamic-structural model of peptide binding to sequences derived from HA H1N1, for which a DR1-restricted classification in dominant, sub-dominant, weak and negative has been established. We measured peptide KD and t1/2, and correlated such measurements to the observed level of immunodominance. Our results show that immunodominant peptides have a binding affinity in the micromolar range in the presence and absence of DM, whereas negative and weak showed no binding, with one exception. Interestingly, DM effect on binding affinity is variable for these peptides, altering their affinity values on a sequence-by-sequence basis with no direct correlation to their level of immunodominance. Variations in complex kinetic stability in the absence of DM did not reflect variations in immunodominance, whereas all peptides showed a faster release in presence of DM. Taken together, our results suggest that there is no a unique peptide-binding or kinetic signature, which can be adopted as a proxy for immunodominance. Further investigation in the thermodynamic components of the binding process is required to corroborate or modify these initial conclusions.

Structural Properties of Potexvirus Coat Proteins Detected by Optical Methods.

It has been shown by X-ray analysis that cores of coat proteins (CPs) from three potexviruses, flexible helical RNA-containing plant viruses, have similar α-helical structure. However, this similarity cannot explain structural lability of potexvirus virions, which is believed to determine their biological activity. Here, we used circular dichroism (CD) spectroscopy in the far UV region to compare optical properties of CPs from three potexviruses with the same morphology and similar structure. CPs from Alternanthera mosaic virus (AltMV), potato aucuba mosaic virus (PAMV), and potato virus X (PVX) have been studied in a free state and in virions. The CD spectrum of AltMV virions was similar to the previously obtained CD spectrum of papaya mosaic virus (PapMV) virions, but differed significantly from the CD spectrum of PAMV virions. The CD spectrum of PAMV virions resembled in its basic characteristics the CD spectrum of PVX virions characterized by molar ellipticity that is abnormally low for α-helical proteins. Homology modeling of the CP structures in AltMV, PAMV, and PVX virions was based on the known high-resolution structures of CPs from papaya mosaic virus and bamboo mosaic virus and confirmed that the structures of the CP cores in all three viruses were nearly identical. Comparison of amino acid sequences of different potexvirus CPs and prediction of unstructured regions in these proteins revealed a possible correlation between specific features in the virion CD spectra and the presence of disordered N-terminal segments in the CPs.

Helical capsids of plant viruses: architecture with structural lability.

Capsids of numerous filamentous and rod-shaped plant viruses possess helical symmetry. In positive-stranded RNA viruses, helical capsids are typically composed of many identical subunits of the viral capsid protein (CP), encapsidating a molecule of viral genomic RNA. Current progress in structural studies of helical plant viruses has revealed differences between filamentous and rod-shaped viruses, both in structural folds of their CPs and in the interactions of CP molecules in their capsids. Many filamentous and rod-shaped viruses have functionally similar lateral inter-subunit contacts on the outer virion surface. Additionally, the extreme N-terminal CP region in filamentous viruses is intrinsically disordered. Taken together, the available data establish a link between the structural features of molecular interactions of CP molecules and the physical properties of helical virions ranging from rigidity to flexibility. Overall, the structure of helical plant viruses is significantly more labile than previously thought, often allowing structural transitions, remodelling and the existence of alternative structural forms of virions. These properties of virions are believed to be functionally significant at certain stages of the viral life cycle, such as during translational activation and cell-to-cell transport. In this review, we discuss structural and functional features of filamentous and rod-shaped virions, highlight their shared features and differences, and lay emphasis on the relationships between the molecular structure of viral capsids and their properties including virion shape, lability and capability of structural remodelling.