Distinct Conformations of SARS-CoV-2 Omicron Spike Protein and Its Interaction with ACE2 and Antibody.

Since November 2021, Omicron has been the dominant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant that causes the coronavirus disease 2019 (COVID-19) and has continuously impacted human health. Omicron sublineages are still increasing and cause increased transmission and infection rates. The additional 15 mutations on the receptor binding domain (RBD) of Omicron spike proteins change the protein conformation, enabling the Omicron variant to evade neutralizing antibodies. For this reason, many efforts have been made to design new antigenic variants to induce effective antibodies in SARS-CoV-2 vaccine development. However, understanding the different states of Omicron spike proteins with and without external molecules has not yet been addressed. In this review, we analyze the structures of the spike protein in the presence and absence of angiotensin-converting enzyme 2 (ACE2) and antibodies. Compared to previously determined structures for the wildtype spike protein and other variants such as alpha, beta, delta, and gamma, the Omicron spike protein adopts a partially open form. The open-form spike protein with one RBD up is dominant, followed by the open-form spike protein with two RBD up, and the closed-form spike protein with the RBD down. It is suggested that the competition between antibodies and ACE2 induces interactions between adjacent RBDs of the spike protein, which lead to a partially open form of the Omicron spike protein. The comprehensive structural information of Omicron spike proteins could be helpful for the efficient design of vaccines against the Omicron variant.

Molecular dynamics study of interactions between polymorphic actin filaments and gelsolin segment-1.

The assembly of protein actin into double-helical filaments promotes many eukaryotic cellular processes that are regulated by actin-binding proteins (ABPs). Actin filaments can adopt multiple conformations, known as structural polymorphism, which possibly influences the interaction between filaments and ABPs. Gelsolin is a Ca2+ -regulated ABP that severs and caps actin filaments. Gelsolin binding modulates filament structure; however, it is not known how polymorphic actin filament structures influence an interaction of gelsolin S1 with the barbed-end of filament. Herein, we investigated how polymorphic structures of actin filaments affect the interactions near interfaces between the gelsolin segment 1 (S1) domain and the filament barbed-end. Using all-atom molecular dynamics simulations, we demonstrate that different tilted states of subunits modulate gelsolin S1 interactions with the barbed-end of polymorphic filaments. Hydrogen bonding and interaction energy at the filament-gelsolin S1 interface indicate distinct conformations of filament barbed ends, resulting in different interactions of gelsolin S1. This study demonstrates that filament's structural multiplicity plays important roles in the interactions of actin with ABPs.

Experimental Realization of Few Layer Two-Dimensional MoS2 Membranes of Near Atomic Thickness for High Efficiency Water Desalination.

A globally imminent shortage of freshwater has been demanding viable strategies for improving desalination efficiencies with the adoption of cost- and energy-efficient membrane materials. The recently explored 2D transition metal dichalcogenides (2D TMDs) of near atomic thickness have been envisioned to offer notable advantages as high-efficiency membranes owing to their structural uniqueness; that is, extremely small thickness and intrinsic atomic porosity. Despite theoretically projected advantages, experimental realization of near atom-thickness 2D TMD-based membranes and their desalination efficiency assessments have remained largely unexplored mainly due to the technical difficulty associated with their seamless large-scale integration. Herein, we report the experimental demonstration of high-efficiency water desalination membranes based on few-layer 2D molybdenum disulfide (MoS2) of only ∼7 nm thickness. Chemical vapor deposition (CVD)-grown centimeter-scale 2D MoS2 layers were integrated onto porous polymeric supports with well-preserved structural integrity enabled by a water-assisted 2D layer transfer method. These 2D MoS2 membranes of near atomic thickness exhibit an excellent combination of high water permeability (>322 L m-2 h-1 bar-1) and high ionic sieving capability (>99%) for various seawater salts including Na+, K+, Ca2+, and Mg2+ with a range of concentrations. Moreover, they present near 100% salt ion rejection rates for actual seawater obtained from the Atlantic coast, significantly outperforming the previously developed 2D MoS2 layer membranes of micrometer thickness as well as conventional reverse osmosis (RO) membranes. Underlying principles behind such remarkably excellent desalination performances are attributed to the intrinsic atomic vacancies inherent to the CVD-grown 2D MoS2 layers as verified by aberration-corrected electron microscopy characterization.

Metal ions affect the formation and stability of amyloid ß aggregates at multiple length scales.

Amyloid ß (Aß) aggregates, which are a hallmark for neurodegenerative disease, are formed through a self-assembly process such as aggregation of Aß peptide chains. This aggregation process depends on the solvent conditions under which the proteins are aggregated. Nevertheless, the underlying mechanism of the ionic effect on the formation and stability of amyloid aggregates has not been fully understood. Here, we report how metal ions play a role in the formation and stability of Aß aggregates at different length scales, i.e. oligomers and fibrils. It is shown that the metal (i.e. zinc or copper) ion increases the stability of Aß oligomers, whereas the metal ion reduces the stability of Aß fibrils. In addition, we found that zinc ions are able to more effectively destabilize fibril structures than copper ions. Metal ion-mediated (de)stabilization of Aß oligomers (or fibrils) is attributed to the critical effect of the metal ion on the ß-sheet rich crystalline structure of the amyloid aggregate and the status of hydrogen bonds within the aggregate. Our study sheds light on the role of the metal ion in stabilizing the amyloid oligomers known as a toxic agent (to functional cells), which is consistent with clinical observation that high concentrations of metal ions are found in patients suffering from neurodegenerative diseases.

Structural analysis of oligomeric and protofibrillar Aß amyloid pair structures considering F20L mutation effects using molecular dynamics simulations.

Aß amyloid proteins are involved in neuro-degenerative diseases such as Alzheimer's, Parkinson's, and so forth. Because of its structurally stable feature under physiological conditions, Aß amyloid protein disrupts the normal cell function. Because of these concerns, understanding the structural feature of Aß amyloid protein in detail is crucial. There have been some efforts on lowering the structural stabilities of Aß amyloid fibrils by decreasing the aromatic residues characteristic and hydrophobic effect. Yet, there is a lack of understanding of Aß amyloid pair structures considering those effects. In this study, we provide the structural characteristics of wildtype (WT) and phenylalanine residue mutation to leucine (F20L) Aß amyloid pair structures using molecular dynamics simulation in detail. We also considered the polymorphic feature of F20L and WT Aß pair amyloids based on the facing ß-strand directions between the amyloid pairs. As a result, we were able to observe the varying effects of mutation, polymorphism, and protofibril lengths on the structural stability of pair amyloids. Furthermore, we have also found that opposite structural stability exists on a certain polymorphic Aß pair amyloids depending on its oligomeric or protofibrillar state, which can be helpful for understanding the amyloid growth mechanism via repetitive fragmentation and elongation mechanism. Proteins 2017; 85:580-592. © 2016 Wiley Periodicals, Inc.

Characterizing Structural Stability of Amyloid Motif Fibrils Mediated by Water Molecules.

In biological systems, structural confinements of amyloid fibrils can be mediated by the role of water molecules. However, the underlying effect of the dynamic behavior of water molecules on structural stabilities of amyloid fibrils is still unclear. By performing molecular dynamics simulations, we investigate the dynamic features and the effect of interior water molecules on conformations and mechanical characteristics of various amyloid fibrils. We find that a specific mechanism induced by the dynamic properties of interior water molecules can affect diffusion of water molecules inside amyloid fibrils, inducing their different structural stabilities. The conformation of amyloid fibrils induced by interior water molecules show the fibrils' different mechanical features. We elucidate the role of confined and movable interior water molecules in structural stabilities of various amyloid fibrils. Our results offer insights not only in further understanding of mechanical features of amyloids as mediated by water molecules, but also in the fine-tuning of the functional abilities of amyloid fibrils for applications.

Mechanical and vibrational characterization of amyloid-like HET-s nanosheets based on the skewed plate theory.

Pathological amyloidogenic prion proteins have a toxic effect on functional cells in the human cerebrum because of poor degradability and the tendency to accumulate in an uncontrolled manner under physiological conditions. HET-s, a fungal prion protein, is known to undergo conformational variations from fibrillar to nanosheet structures during a change from low to high pH conditions. It has been said that this conformational change can lead to self-propagation by nucleating on the lateral surface of singlet fibrils. Efforts have been made toward the mechanical characterization of fibrillar amyloids, but a global understanding of amyloid-like HET-s nanosheet structures is lacking. In this study, we analyzed the mechanical and vibrational characteristics of the skewed HET-s nanosheet structures that developed under neutral pH conditions by performing various molecular dynamics simulations. By applying the skewed plate theory to HET-s nanosheets for various length scales with numerous pores inside the structures, we found that the skewed HET-s nanosheet structure has mechanical properties comparable to those of previously reported biological film materials and nanomaterials. Considering the inherent characteristics of structural stability, our observation provides valuable and detailed structural information on skewed amyloid-like HET-s nanosheets.

Sodium chloride's effect on self-assembly of diphenylalanine bilayer.

Understanding self-assembling peptides becomes essential in nanotechnology, thereby providing a bottom-up method for fabrication of nanostructures. Diphenylalanine constitutes an outstanding building block that can be assembled into various nanostructures, including two-dimensional bilayers or nanotubes, exhibiting superb mechanical properties. It is known that the effect of the ions is critical in conformational and chemical interactions of bilayers or membranes. In this study, we analyzed the effect of sodium chloride on diphenylalanine bilayer using coarse-grained molecular dynamics simulations, and calculated the bending Young's modulus and the torsional modulus by applying normal modal analysis using an elastic network model. The results showed that sodium chloride dramatically increases the assembling efficiency and stability, thereby promising to allow the precise design and control of the fabrication process and properties of bio-inspired materials. © 2016 Wiley Periodicals, Inc.

End Capping Alters the Structural Characteristics and Mechanical Properties of Transthyretin (105-115) Amyloid Protofibrils.

Pathological amyloid proteins are associated with degenerative and neurodegenerative diseases. These amyloid proteins develop as oligomer, fibrillar, and plaque forms, due to the denatured and unstable status of the amyloid monomers. Specifically, the development of fibrillar amyloid proteins has been investigated through several experimental studies. To understand the generation of amyloid fibrils, environmental factors such as point mutations, pH, and polymorphic characteristics have been considered. Recently, amyloid fibril studies related to end-capping effects have been conducted to understand amyloid fibril development. However, atomic-level studies to determine the stability and mechanical properties of amyloid fibrils based on end capping have not been undertaken. In this study, we show that end capping alters the structural characteristics and conformations of transthyretin (TTR) amyloid fibrils by using molecular dynamics (MD) simulations. Variation in the structural conformations and characteristics of the TTR fibrils through end capping are observed, due to the resulting electrostatic energies and hydrophobicity characteristics. Moreover, the end capping changes the mechanical properties of TTR fibrils. Our results shed light on amyloid fibril formation under end-capping conditions.

Mechanical behavior comparison of spider and silkworm silks using molecular dynamics at atomic scale.

Spider and silkworm silk proteins have received much attention owing to their inherent structural stability, biodegradability, and biocompatibility. These silk protein materials have various mechanical characteristics such as elastic modulus, ultimate strength and fracture toughness. While the considerable mechanical characteristics of the core crystalline regions of spider silk proteins at the atomistic scale have been investigated through several experimental techniques and computational studies, there is a lack of comparison between spider and silkworm fibroins in the atomistic scale. In this study, we investigated the differences between the mechanical characteristics of spider and silkworm fibroin structures by applying molecular dynamics and steered molecular dynamics. We found that serine amino acids in silkworm fibroins not only increased the number of hydrogen bonds, but also altered their structural characteristics and mechanical properties.

Effects of lysine residues on structural characteristics and stability of tau proteins.

Pathological amyloid proteins have been implicated in neuro-degenerative diseases, specifically Alzheimer's, Parkinson's, Lewy-body diseases and prion related diseases. In prion related diseases, functional tau proteins can be transformed into pathological agents by environmental factors, including oxidative stress, inflammation, Aß-mediated toxicity and covalent modification. These pathological agents are stable under physiological conditions and are not easily degraded. This un-degradable characteristic of tau proteins enables their utilization as functional materials to capturing the carbon dioxides. For the proper utilization of amyloid proteins as functional materials efficiently, a basic study regarding their structural characteristic is necessary. Here, we investigated the basic tau protein structure of wild-type (WT) and tau proteins with lysine residues mutation at glutamic residue (Q2K) on tau protein at atomistic scale. We also reported the size effect of both the WT and Q2K structures, which allowed us to identify the stability of those amyloid structures.

Morphology and mechanical properties of multi-stranded amyloid fibrils probed by atomistic and coarse-grained simulations.

Amyloid fibrils are responsible for pathogenesis of various diseases and exhibit the structural feature of an ordered, hierarchical structure such as multi-stranded helical structure. As the multi-strandedness of amyloid fibrils has recently been found to be highly correlated with their toxicity and infectivity, it is necessary to study how the hierarchical (i.e. multi-stranded) structure of amyloid fibril is formed. Moreover, although it has recently been reported that the nanomechanics of amyloid proteins plays a key role on the amyloid-induced pathogenesis, a critical role that the multi-stranded helical structure of the fibrils plays in their nanomechanical properties has not fully characterized. In this work, we characterize the morphology and mechanical properties of multi-stranded amyloid fibrils by using equilibrium molecular dynamics simulation and elastic network model. It is shown that the helical pitch of multi-stranded amyloid fibril is linearly proportional to the number of filaments comprising the amyloid fibril, and that multi-strandedness gives rise to improving the bending rigidity of the fibril. Moreover, we have also studied the morphology and mechanical properties of a single protofilament (filament) in order to understand the effect of cross-ß structure and mutation on the structures and mechanical properties of amyloid fibrils. Our study sheds light on the underlying design principles showing how the multi-stranded amyloid fibril is formed and how the structure of amyloid fibrils governs their nanomechanical properties.

Influence of Aromatic Residues on the Material Characteristics of Aß Amyloid Protofibrils at the Atomic Scale.

Amyloid fibrils, which cause a number of degenerative diseases, are insoluble under physiological conditions and are supported by native contacts. Recently, the effects of the aromatic residues on the Aß amyloid protofibril were investigated in a ThT fluorescence study. However, the relationship between the material characteristics of the Aß protofibril and its aromatic residues has not yet been investigated on the atomic scale. Here, we successfully constructed wild-type (WT) and mutated types of Aß protofibrils by using molecular dynamics simulations. Through principle component analysis, we established the structural stability and vibrational characteristics of F20L Aß protofibrils and compared them with WT and other mutated models such as F19L and F19LF20L. In addition, structural stability was assessed by calculating the elastic modulus, which showed that the F20L model has higher values than the other models studied. From our results, it is shown that aromatic residues influence the structural and material characteristics of Aß protofibrils.

Endothelial leakiness elicited by amyloid protein aggregation.

Alzheimer's disease (AD) is a major cause of dementia debilitating the global ageing population. Current understanding of the AD pathophysiology implicates the aggregation of amyloid beta (Aß) as causative to neurodegeneration, with tauopathies, apolipoprotein E and neuroinflammation considered as other major culprits. Curiously, vascular endothelial barrier dysfunction is strongly associated with Aß deposition and 80-90% AD subjects also experience cerebral amyloid angiopathy. Here we show amyloid protein-induced endothelial leakiness (APEL) in human microvascular endothelial monolayers as well as in mouse cerebral vasculature. Using signaling pathway assays and discrete molecular dynamics, we revealed that the angiopathy first arose from a disruption to vascular endothelial (VE)-cadherin junctions exposed to the nanoparticulates of Aß oligomers and seeds, preceding the earlier implicated proinflammatory and pro-oxidative stressors to endothelial leakiness. These findings were analogous to nanomaterials-induced endothelial leakiness (NanoEL), a major phenomenon in nanomedicine depicting the paracellular transport of anionic inorganic nanoparticles in the vasculature. As APEL also occurred in vitro with the oligomers and seeds of alpha synuclein, this study proposes a paradigm for elucidating the vascular permeation, systemic spread, and cross-seeding of amyloid proteins that underlie the pathogeneses of AD and Parkinson's disease.

Molecular Basis for Actin Polymerization Kinetics Modulated by Solution Crowding.

Actin polymerization drives cell movement and provides cells with structural integrity. Intracellular environments contain high concentrations of solutes, including organic compounds, macromolecules, and proteins. Macromolecular crowding has been shown to affect actin filament stability and bulk polymerization kinetics. However, the molecular mechanisms behind how crowding influences individual actin filament assembly are not well understood. In this study, we investigated how crowding modulates filament assembly kinetics using total internal reflection fluorescence (TIRF) microscopy imaging and pyrene fluorescence assays. The elongation rates of individual actin filaments analyzed from TIRF imaging depended on the type of crowding agent (polyethylene glycol, bovine serum albumin, and sucrose) as well as their concentrations. Further, we utilized all-atom molecular dynamics (MD) simulations to evaluate the effects of crowding molecules on the diffusion of actin monomers during filament assembly. Taken together, our data suggest that solution crowding can regulate actin assembly kinetics at the molecular level.

Anionic nanoplastic exposure induces endothelial leakiness.

The global-scale production of plastics has been instrumental in advancing modern society, while the rising accumulation of plastics in landfills, oceans, and anything in between has become a major stressor on environmental sustainability, climate, and, potentially, human health. While mechanical and chemical forces of man and nature can eventually break down or recycle plastics, our understanding of the biological fingerprints of plastics, especially of nanoplastics, remains poor. Here we report on a phenomenon associated with the nanoplastic forms of anionic polystyrene and poly(methyl methacrylate), where their introduction disrupted the vascular endothelial cadherin junctions in a dose-dependent manner, as revealed by confocal fluorescence microscopy, signaling pathways, molecular dynamics simulations, as well as ex vivo and in vivo assays with animal model systems. Collectively, our results implicated nanoplastics-induced vasculature permeability as primarily biophysical-biochemical in nature, uncorrelated with cytotoxic events such as reactive oxygen species production, autophagy, and apoptosis. This uncovered route of paracellular transport has opened up vast avenues for investigating the behaviour and biological effects of nanoplastics, which may offer crucial insights for guiding innovations towards a sustainable plastics industry and environmental remediation.

Crowding tunes the organization and mechanics of actin bundles formed by crosslinking proteins.

Fascin and α-actinin form higher-ordered actin bundles that mediate numerous cellular processes including cell morphogenesis and movement. While it is understood crosslinked bundle formation occurs in crowded cytoplasm, how crowding affects the bundling activities of the two crosslinking proteins is not known. Here, we demonstrate how solution crowding modulates the organization and mechanical properties of fascin- and α-actinin-induced bundles, utilizing total internal reflection fluorescence and atomic force microscopy imaging. Molecular dynamics simulations support the inference that crowding reduces binding interaction between actin filaments and fascin or the calponin homology 1 domain of α-actinin evidenced by interaction energy and hydrogen bonding analysis. Based on our findings, we suggest a mechanism of crosslinked actin bundle assembly and mechanics in crowded intracellular environments.

A Framework of Paracellular Transport via Nanoparticles-Induced Endothelial Leakiness.

Nanomaterial-induced endothelial leakiness (NanoEL) is an interfacial phenomenon denoting the paracellular transport of nanoparticles that is pertinent to nanotoxicology, nanomedicine and biomedical engineering. While the NanoEL phenomenon is complementary to the enhanced permeability and retention effect in terms of their common applicability to delineating the permeability and behavior of nanoparticles in tumoral environments, these two effects significantly differ in scope, origin, and manifestation. In the current study, the descriptors are fully examined of the NanoEL phenomenon elicited by generic citrate-coated gold nanoparticles (AuNPs) of changing size and concentration, from microscopic gap formation and actin reorganization down to molecular signaling pathways and nanoscale interactions of AuNPs with VE-cadherin and its intra/extracellular cofactors. Employing synergistic in silico methodologies, for the first time the molecular and statistical mechanics of cadherin pair disruption, especially in response to AuNPs of the smallest size and highest concentration are revealed. This study marks a major advancement toward establishing a comprehensive NanoEL framework for complementing the understanding of the transcytotic pathway and for guiding the design and application of future nanomedicines harnessing the myriad functions of the mammalian vasculature.

Investigation of the role hydrophobin monomer loops using hybrid models via molecular dynamics simulation.

Hydrophobins are small amphiphilic fungal proteins that are highly surface-active and are used in various industrial applications such as dispersion, immobilization, and antifouling. At hydrophobic-hydrophilic interfaces, hydrophobins tend to self-assemble as rodlets or monolayers, depending on whether they are class I or II. Several studies have determined the three-dimensional structure and investigated the self-assembly formation mechanism of the class I EAS from Neurospora crassa and the class II HFBII from Trichoderma reesei. Although some studies have examined the performance of chimeric hydrophobins, they have not been investigated at the atomic scale. Here, we designed chimeric hydrophobins by grafting the L1 loop of Vmh2 and the L3 loop of EAS onto the class II hydrophobin HFBII by homology modeling and performed vacuum-water interface molecular simulations to determine their structural behaviors. We found that the chimeric hydrophobin grafted with the L3 of EAS became unstable under standard conditions, whereas that grafted with the L1 of Vmh2 became unstable in the presence of calcium ions. Moreover, when both the EAS L3 and Vmh2 L1 were grafted together, the structure became disordered and lost its amphiphilic characteristics in standard conditions. In the presence of calcium, however, its structural stability was restored. However, an additional external perturbation is required to trigger the conformational transition. Although our chimeric hydrophobin models were designed through homology modeling, our results provide detailed information regarding hydrophobin self-assembly and their surface-interactive behavior that may serve as a template for designing hydrophobins for future industrial applications.

Actin Filament Mechanics and Structure in Crowded Environments.

The cellular environment is crowded with high concentrations of macromolecules that significantly reduce accessible volume for biomolecular interactions. Reductions in cellular volume can generate depletion forces that affect protein assembly and stability. The mechanical and structural properties of actin filaments play critical roles in various cellular functions, including structural support, cell movement, division, and intracellular transport. Although the effects of molecular crowding on actin polymerization have been shown, how crowded environments affect filament mechanics and structure is unknown. In this study, we investigate the effects of solution crowding on the modulations of actin filament bending stiffness and conformations both in vitro and in silico. Direct visualization of thermally fluctuating filaments in the presence of crowding agents is achieved by fluorescence microscopy imaging. Biophysical analysis indicates that molecular crowding enhances filament's effective bending stiffness and reduces average filament lengths. Utilizing the all-atom molecular dynamics simulations, we demonstrate that molecular crowding alters filament conformations and intersubunit contacts that are directly coupled to the mechanical properties of filaments. Taken together, our study suggests that the interplay between excluded volume effects and nonspecific interactions raised from molecular crowding may modulate actin filament mechanics and structure.