Direct evidence for flat bands in twisted bilayer graphene from nano-ARPES

Transport experiments in twisted bilayer graphene revealed multiple superconducting domes separated by correlated insulating states. These properties are generally associated with strongly correlated states in a flat mini-band of the hexagonal moir\'e superlattice as it was predicted by band structure calculations. Evidence for such a flat band comes from local tunneling spectroscopy and electronic compressibility measurements, reporting two or more sharp peaks in the density of states that may be associated with closely spaced van Hove singularities. Direct momentum resolved measurements proved difficult though. Here, we combine different imaging techniques and angle resolved photoemission with simultaneous real and momentum space resolution (nano-ARPES) to directly map the band dispersion in twisted bilayer graphene devices near charge neutrality. Our experiments reveal large areas with homogeneous twist angle that support a flat band with spectral weight that is highly localized in momentum space. The flat band is separated from the dispersive Dirac bands which show multiple moir\'e hybridization gaps. These data establish the salient features of the twisted bilayer graphene band structure.Comment: Submitted to Nature Materials. Nat. Phys. (2020

Lysosomal and vacuolar sorting: not so different after all!

Soluble hydrolases represent the main proteins of lysosomes and vacuoles and are essential to sustain the lytic properties of these organelles typical for the eukaryotic organisms. The sorting of these proteins from ER residents and secreted proteins is controlled by highly specific receptors to avoid mislocalization and subsequent cellular damage. After binding their soluble cargo in the early stage of the secretory pathway, receptors rely on their own sorting signals to reach their target organelles for ligand delivery, and to recycle back for a new round of cargo recognition. Although signals in cargo and receptor molecules have been studied in human, yeast and plant model systems, common denominators and specific examples of diversification have not been systematically explored. This review aims to fill this niche by comparing the structure and the function of lysosomal/vacuolar sorting receptors (VSRs) from these three organisms

Fluorescent mannosides serve as acceptor substrates for glycosyltransferase and sugar-1-phosphate transferase activities in <i>Euglena gracilis</i> membranes

Synthetic hexynyl α-D-mannopyranoside and its α-1,6-linked disaccharide counterpart were fluorescently labelled through CuAAC click chemistry with 3-azido-7-hydroxycoumarin. The resulting triazolyl-coumarin adducts, which were amenable to analysis by TLC, HPLC and mass spectrometry, proved to be acceptor substrates for α-1,6-ManT activities in mycobacterial membranes, as well as α- and β-GalT activities in trypanosomal membranes, benchmarking the potential of the fluorescent acceptor approach against earlier radiochemical assays. Following on to explore the glycobiology of the benign protozoan alga Euglena gracilis, α-1,3- and α-1,2-ManT activities were detected in membrane preparations, along with GlcT, Glc-P-T and GlcNAc-P-T activities. These studies serve to demonstrate the potential of readily accessible fluorescent glycans as substrates for exploring carbohydrate active enzymes

Eukaryotic Flagella: Variations in Form, Function, and Composition during Evolution

The microtubule axoneme is an iconic structure in eukaryotic cell biology and the defining structure in all eukaryotic flagella (or cilia). Flagella occur in taxa spanning the breadth of eukaryotic evolution, which indicates that the organelle's origin predates the radiation of extant eukaryotes from a last common ancestor. During evolution, the flagellar architecture has been subject to both elaboration and moderation. Even conservation of 9+2 architecture—the classic microtubule configuration seen in most axonemes—belies surprising variation in protein content. Classically considered as organelles of motility that support cell swimming or fast movement of material across a cell surface, it is now clear that the functions of flagella are also far broader; for instance, the involvement of flagella in sensory perception and protein secretion has recently been made evident in both protists and animals. Here, we review and discuss, in an evolutionary context, recent advances in our understanding of flagellum function and composition

The Canine Oral Microbiome

Determining the bacterial composition of the canine oral microbiome is of interest for two primary reasons. First, while the human oral microbiome has been well studied using molecular techniques, the oral microbiomes of other mammals have not been studied in equal depth using culture independent methods. This study allows a comparison of the number of bacterial taxa, based on 16S rRNA-gene sequence comparison, shared between humans and dogs, two divergent mammalian species. Second, canine oral bacteria are of interest to veterinary and human medical communities for understanding their roles in health and infectious diseases. The bacteria involved are mostly unnamed and not linked by 16S rRNA-gene sequence identity to a taxonomic scheme. This manuscript describes the analysis of 5,958 16S rRNA-gene sequences from 65 clone libraries. Full length 16S rRNA reference sequences have been obtained for 353 canine bacterial taxa, which were placed in 14 bacterial phyla, 23 classes, 37 orders, 66 families, and 148 genera. Eighty percent of the taxa are currently unnamed. The bacterial taxa identified in dogs are markedly different from those of humans with only 16.4% of oral taxa are shared between dogs and humans based on a 98.5% 16S rRNA sequence similarity cutoff. This indicates that there is a large divergence in the bacteria comprising the oral microbiomes of divergent mammalian species. The historic practice of identifying animal associated bacteria based on phenotypic similarities to human bacteria is generally invalid. This report describes the diversity of the canine oral microbiome and provides a provisional 16S rRNA based taxonomic scheme for naming and identifying unnamed canine bacterial taxa

Outcomes from elective colorectal cancer surgery during the SARS-CoV-2 pandemic

This study aimed to describe the change in surgical practice and the impact of SARS-CoV-2 on mortality after surgical resection of colorectal cancer during the initial phases of the SARS-CoV-2 pandemic

British Romanticism and the Global Climate

As a result of developments in the meteorological and geological sciences, the Romantic period saw the gradual emergence of attempts to understand the climate as a dynamic global system that could potentially be affected by human activity. This chapter examines textual responses to climate disruption cause by the Laki eruption of 1783 and the Tambora eruption of 1815. During the Laki haze, writers such as Horace Walpole, Gilbert White, and William Cowper found in Milton a powerful way of understanding the entanglements of culture and climate at a time of national and global crisis. Apocalyptic discourse continued to resonate during the Tambora crisis, as is evident in eyewitness accounts of the eruption, in the utopian predictions of John Barrow and Eleanor Anne Porden, and in the grim speculations of Byron’s ‘Darkness’. Romantic writing offers a powerful analogue for thinking about climate change in the Anthropocene