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The morphological changes of phosphonate polypeptoid electrolyte membranes, poly-N-(2-ethyl)hexylglycine-biocfc-poly-N-phosphonomethylglycine (pNehm-b-pNpmn), in hydrated and dry states were characterized by cryogenic transmission electron microscopy (cryo-TEM) and cryogenic electron tomography (ciyo-ET). The analysis of 3D tomograms revealed that the [pNeh.sub.9]-b[pNpm.sub.9] thin films absorbed a large amount of water, resulting in the formation of membranes that were nearly flat and giant multicompartment vesicles dispersed in the water phase. A simple lamellar phase appeared when the films were dried. In contrast, [pNeh.sub.18]-b-[pNpm.sub.18] thin films absorbed little water and formed small highly curved unilamellar and multilamellar vesicles. Water was located mainly outside the closely-packed vesicles. When water was removed by drying, the walls of adjacent vesicles collapsed to form honeycomb-like capsules. The changes in domain size reflected changes in chain conformations. The pNpmg blocks were saturated by water and fully extended, while [pNpm.sub.18] blocks were neither saturated by water nor fully extended. In addition, the thicknesses of hydrophobic blocks in the hydrated films of both [pNeh.sub.9]-fepNpmg and [pNeh.sub.18]-b-[pNpm.sub.18] were smaller than those in the dry films, reflecting an increase of the average distance between the neighboring junctions of polypeptoid molecules. KEYWORDS cryogenic, electron tomography, low-dose, polymer electrolyte membrane, polypeptoid, transmission electron microscopy, 1 | INTRODUCTION Polymer electrolyte membranes have attracted considerable attention in recent years due to their application in fuel cells, [1,2] lithium-ion batteries, [3,4] and artificial photosynthesis. [5] These polymers [...]

Protein crystallization is important in structural biology, disease research and pharmaceuticals. It has recently been recognized that nonclassical crystallization--involving initial formation of an amorphous precursor phase--occurs often in protein, organic and inorganic crystallization processes.sup.1-5. A two-step nucleation theory has thus been proposed, in which initial low-density, solvated amorphous aggregates subsequently densify, leading to nucleation.sup.4,6,7. This view differs from classical nucleation theory, which implies that crystalline nuclei forming in solution have the same density and structure as does the final crystalline state.sup.1. A protein crystallization mechanism involving this classical pathway has recently been observed directly.sup.8. However, a molecular mechanism of nonclassical protein crystallization.sup.9-15 has not been established.sup.9,11,14. To determine the nature of the amorphous precursors and whether crystallization takes place within them (and if so, how order develops at the molecular level), three-dimensional (3D) molecular-level imaging of a crystallization process is required. Here we report cryogenic scanning transmission microscopy tomography of ferritin aggregates at various stages of crystallization, followed by 3D reconstruction using simultaneous iterative reconstruction techniques to provide a 3D picture of crystallization with molecular resolution. As crystalline order gradually increased in the studied aggregates, they exhibited an increase in both order and density from their surface towards their interior. We observed no highly ordered small structures typical of a classical nucleation process, and occasionally we observed several ordered domains emerging within one amorphous aggregate, a phenomenon not predicted by either classical or two-step nucleation theories. Our molecular-level analysis hints at desolvation as the driver of the continuous order-evolution mechanism, a view that goes beyond current nucleation models, yet is consistent with a broad spectrum of protein crystallization mechanisms. Cryo-STEM tomography of ferritin crystallization is used to reveal nonclassical evolution of crystalline order, indicating that it may be desolvation that drives the continuous evolution of order in crystallization., Author(s): Lothar Houben [sup.1] , Haim Weissman [sup.2] , Sharon G. Wolf [sup.1] , Boris Rybtchinski [sup.2] Author Affiliations: (1) Department of Chemical Research Support, Weizmann Institute of Science, Rehovot, [...]

Cutting-edge microscopy techniques are allowing researchers to spy on the innards of cells in all their crowded glory. Cutting-edge microscopy techniques are allowing researchers to spy on the innards of cells in all their crowded glory., Author(s): Diana Kwon Author Affiliations: Cryo-electron tomography and related techniques can showcase the insides of cells in striking detail. Credit: S. Albert et al ./PNAS (CC BY 4.0) Cryo-electron tomography [...]

BREAKING GROUND ON STRONGER ALLOYS In a breakthrough for alloy research, scientists from the U.K.'s University of Birmingham have detailed how microscopic crystals grow and change shape in molten metals [...]

Eukaryotic cells traffic proteins and lipids between different compartments using protein-coated vesicles and tubules. The retromer complex is required to generate cargo-selective tubulovesicular carriers from endosomal membranes.sup.1-3. Conserved in eukaryotes, retromer controls the cellular localization and homeostasis of hundreds of transmembrane proteins, and its disruption is associated with major neurodegenerative disorders.sup.4-7. How retromer is assembled and how it is recruited to form coated tubules is not known. Here we describe the structure of the retromer complex (Vps26-Vps29-Vps35) assembled on membrane tubules with the bin/amphiphysin/rvs-domain-containing sorting nexin protein Vps5, using cryo-electron tomography and subtomogram averaging. This reveals a membrane-associated Vps5 array, from which arches of retromer extend away from the membrane surface. Vps35 forms the 'legs' of these arches, and Vps29 resides at the apex where it is free to interact with regulatory factors. The bases of the arches connect to each other and to Vps5 through Vps26, and the presence of the same arches on coated tubules within cells confirms their functional importance. Vps5 binds to Vps26 at a position analogous to the previously described cargo- and Snx3-binding site, which suggests the existence of distinct retromer-sorting nexin assemblies. The structure provides insight into the architecture of the coat and its mechanism of assembly, and suggests that retromer promotes tubule formation by directing the distribution of sorting nexin proteins on the membrane surface while providing a scaffold for regulatory-protein interactions.The retromer complex (the vacuolar protein sorting heterotrimer Vps26-Vps29-Vps35) has been resolved in association with membranes and the sorting nexin protein Vps5 using cryo-electron tomography., Author(s): Oleksiy Kovtun [sup.1] [sup.2] , Natalya Leneva [sup.3] [sup.4] , Yury S. Bykov [sup.1] [sup.2] , Nicholas Ariotti [sup.3] [sup.6] , Rohan D. Teasdale [sup.3] [sup.7] , Miroslava Schaffer [...]

Earths body tidealso known as the solid Earth tide, the displacement of the solid Earths surface caused by gravitational forces from the Moon and the Sunis sensitive to the density of the two Large Low Shear Velocity Provinces (LLSVPs) beneath Africa and the Pacific. These massive regions extend approximately 1,000 kilometres upward from the base of the mantle and their buoyancy remains actively debated within the geophysical community. Here we use tidal tomography to constrain Earths deep-mantle buoyancy derived from Global Positioning System (GPS)-based measurements of semi-diurnal body tide deformation. Using a probabilistic approach, we show that across the bottom two-thirds of the two LLSVPs the mean density is about 0.5 per cent higher than the average mantle density across this depth range (that is, its mean buoyancy is minus 0.5 per cent), although this anomaly may be concentrated towards the very base of the mantle. We conclude that the buoyancy of these structures is dominated by the enrichment of high-density chemical components, probably related to subducted oceanic plates or primordial material associated with Earths formation. Because the dynamics of the mantle is driven by density variations, our result has important dynamical implications for the stability of the LLSVPs and the long-term evolution of the Earth system., Author(s): Harriet C. P. Lau (corresponding author) [1]; Jerry X. Mitrovica [1]; James L. Davis [2]; Jeroen Tromp [3]; Hsin-Ying Yang [4, 5]; David Al-Attar [6] Earths elastic structure and [...]