Races to Modernity Behrends, Jan C; Kohlrausch, Martin
2014, 20140830, 2014-07-20
eBook
This volume succeeds beautifully in conveying a detailed sense of urban development in Eastern Europe and the crucial importance of cities for the moderniszation of Eastern Europe during the half ...century before World War II.
Supersymmetry is a powerful concept in quantum many-body physics. It helps to illuminate ground-state properties of complex quantum systems and gives relations between correlation functions. In this ...Letter, we show that the Sachdev–Ye–Kitaev model, in its simplest form of Majorana fermions with random four-body interactions, is supersymmetric. In contrast to existing explicitly supersymmetric extensions of the model, the supersymmetry we find requires no relations between couplings. The type of supersymmetry and the structure of the supercharges are entirely set by the number of interacting Majorana modes and are thus fundamentally linked to the model's Altland–Zirnbauer classification. The supersymmetry we uncover has a natural interpretation in terms of a one-dimensional topological phase supporting Sachdev–Ye–Kitaev boundary physics and has consequences away from the ground state, including in q-body dynamical correlation functions.
Efforts to sequence single protein molecules in nanopores
have been hampered by the lack of techniques with sufficient sensitivity to discern the subtle molecular differences among all twenty amino ...acids. Here we report ionic current detection of all twenty proteinogenic amino acids in an aerolysin nanopore with the help of a short polycationic carrier. Application of molecular dynamics simulations revealed that the aerolysin nanopore has a built-in single-molecule trap that fully confines a polycationic carrier-bound amino acid inside the sensing region of the aerolysin. This structural feature means that each amino acid spends sufficient time in the pore for sensitive measurement of the excluded volume of the amino acid. We show that distinct current blockades in wild-type aerolysin can be used to identify 13 of the 20 natural amino acids. Furthermore, we show that chemical modifications, instrumentation advances and nanopore engineering offer a route toward identification of the remaining seven amino acids. These findings may pave the way to nanopore protein sequencing.
Electrophysiological studies of the interaction of polymers with pores formed by bacterial toxins (1) provide a window on single molecule interaction with proteins in real time, (2) report on the ...behavior of macromolecules in confinement, and (3) enable label-free single molecule sensing. Using pores formed by the staphylococcal toxin α-hemolysin (aHL), a particularly pertinent observation was that, under high salt conditions (3–4 M KCl), the current through the pore is blocked for periods of hundreds of microseconds to milliseconds by poly(ethylene glycol) (PEG) oligomers (degree of polymerization approximately 10–60). Notably, this block showed monomeric sensitivity on the degree of polymerization of individual oligomers, allowing the construction of size or mass spectra from the residual current values. Here, we show that the current through the pore formed by aerolysin (AeL) from Aeromonas hydrophila is also blocked by PEG but with drastic differences in the voltage-dependence of the interaction. In contrast to aHL, AeL strongly binds PEG at high transmembrane voltages. This fact, which is likely related to AeL’s highly charged pore wall, allows discrimination of polymer sizes with particularly high resolution. Multiple applications are now conceivable with this pore to screen various nonionic or charged polymers.
The chemical nature and precise position of posttranslational modifications (PTMs) in proteins or peptides are crucial for various severe diseases, such as cancer. State-of-the-art PTM diagnosis is ...based on elaborate and costly mass-spectrometry or immunoassay-based approaches, which are limited in selectivity and specificity. Here, we demonstrate the use of a protein nanopore to differentiate peptidesderived from human histone H4 proteinof identical mass according to the positions of acetylated and methylated lysine residues. Unlike sequencing by stepwise threading, our method detects PTMs and their positions by sensing the shape of a fully entrapped peptide, thus eliminating the need for controlled translocation. Molecular dynamics simulations show that the sensitivity to molecular shape derives from a highly nonuniform electric field along the pore. This molecular shape-sensing principle offers a path to versatile, label-free, and high-throughput characterizations of protein isoforms.
Two-dimensional second-order topological superconductors host zero-dimensional Majorana bound states at their boundaries. In this work, focusing on rotation-invariant crystalline topological ...superconductors, we establish a bulk-boundary correspondence linking the presence of such Majorana bound states to bulk topological invariants introduced by Benalcazar et al. Phys. Rev. B 89, 224503 (2014). We thus establish when a topological crystalline superconductor protected by rotational symmetry displays second-order topological superconductivity. Our approach is based on stacked Dirac Hamiltonians, using which we relate transitions between topological phases to the transformation properties between adjacent gapped boundaries. We find that, in addition to the bulk rotational invariants, the presence of Majorana boundary bound states in a given geometry depends on the interplay between weak topological invariants and the location of the rotation center relative to the lattice. We provide numerical examples for our predictions and discuss possible extensions of our approach.
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