Cadherin cell-cell adhesion proteins play key roles in tissue morphogenesis and wound healing. Cadherin ectodomains bind in two conformations, X-dimers and strand-swap dimers, with different adhesive ...properties. However, the mechanisms by which cells regulate ectodomain conformation are unknown. Cadherin intracellular regions associate with several actin-binding proteins including vinculin, which are believed to tune cell-cell adhesion by remodeling the actin cytoskeleton. Here, we show at the single-molecule level, that vinculin association with the cadherin cytoplasmic region allosterically converts weak X-dimers into strong strand-swap dimers and that this process is mediated by myosin II-dependent changes in cytoskeletal tension. We also show that in epithelial cells, ∼70% of apical cadherins exist as strand-swap dimers while the remaining form X-dimers, providing two cadherin pools with different adhesive properties. Our results demonstrate the inside-out regulation of cadherin conformation and establish a mechanistic role for vinculin in this process.
Cadherins are essential cell–cell adhesion proteins that interact in two distinct conformations: X‐dimers and strand‐swap dimers. Both X‐dimers and strand‐swap dimers are thought to exclusively rely ...on symmetric sets of interactions between key amino acids on both cadherin binding partners. Here, we use single‐molecule atomic force microscopy and computer simulations to show that symmetry in cadherin binding is dispensable and that cadherins can also interact in a novel conformation that asymmetrically incorporates key elements of both strand‐swap dimers and X‐dimers. Our results clarify the biophysical rules for cadherin binding and demonstrate that cadherins interact in a more diverse range of conformations than previously understood.
Cadherins are essential cell–cell adhesion proteins that bind in two distinct conformations, via symmetric interactions between both binding partners. Here, we show that symmetry in cadherin binding is dispensable and that cadherins can interact in a novel asymmetric conformation.
Classical cadherins are transmembrane, Ca2+-dependent, cell-cell adhesion proteins that are essential for formation and maintenance of tissues. Cadherin extracellular region mediates cell-cell ...adhesion by binding in two different trans conformations– X-dimers and strand-swap dimers– that have different biophysical properties. While bond mechanics of different cadherin conformations have been extensively studied, how these conformations are utilized and regulated in cells is completely unknown. In the first part of this dissertation, I use single-molecule force measurements with an Atomic Force Microscope (AFM) on the surface of live cells to show that cadherin ectodomain conformations are regulated from within the cell in an inside-out manner. Association of vinculin to the cytoplasmic region of cadherin drives the conversion of a weaker X-dimer to a stronger strand-swap dimer in a cytoskeleton tension dependent manner.While two different conformations cadherin dimers adopt are believed to be formed due to symmetric interactions of key amino acids that are involved in bond formation, it is unknown whether this symmetry is obligatory for cadherin dimerization. In the second part of this dissertation, I integrate AFM-based single-molecule force measurements in a cell-free context with molecular dynamics simulations to show that cadherins can form asymmetric trans dimers. These asymmetric cadherin dimers are weaker than corresponding symmetric dimers and are mostly trapped in the weaker, X-dimer conformation.
Classical cadherin and desmosomal cadherin cell–cell adhesion proteins play essential roles in tissue morphogenesis and in maintaining tissue integrity. Deficiencies in cadherin adhesion are ...hallmarks of diseases such as cancers, skin diseases, and cardiomyopathies. Structural studies and single-molecule biophysical measurements have revealed critical similarities and surprising differences between these key adhesion proteins. This review summarizes our current understanding of the biophysics of classical and desmosomal cadherin adhesion and the molecular basis for their cross talk. We focus on recent single-molecule measurements, highlight key insights into the adhesion of cadherin extracellular regions and their relation to associated diseases, and identify major open questions in this exciting area of research.
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The all-particle cosmic ray energy spectrum is an important tool to study acceleration and propagation mechanisms of cosmic rays. The main goal of this dissertation is to lower the energy threshold ...of the all-particle cosmic ray energy spectrum to overlap with the energy spectra from direct measurements. Previous studies with IceTop/IceCube have measured the spectrum from PeV to EeV. Those measurements used events with at least five-stations hit. In this study, events with two or more stations are used to measure the energy spectrum from 250 TeV to 10 PeV.In addition to lowering the threshold of the cosmic-ray energy spectrum, this thesis also includes a preliminary application of the constant intensity cut method to IceTop data. This method has the potential to improve the reach of IceTop in the EeV range.To lower the energy threshold of IceTop, a new trigger and filter is developed and is implemented since May 20, 2016. The new trigger and filter uses 4 pairs of nearby infill stations where the separation between stations in each pair is less than 50 m. Data from the entire array are collected for events in which at least one infill pair is hit. Data to calculate the energy spectrum are collected from May 2016 to April 2017 with a livetime (duration) of 330.43 days. A total of 7,442,086 events is used after all quality cuts.The constant intensity cut (CIC) method is a widely used method to calculate the cosmic ray energy spectrum. The method increases statistics in energy spectrum analysis by including air showers from higher zenith angle. In this dissertation, CIC is used in particular to study atmospheric attenuation and to measure indirectly the energy-dependent average shower maximum (⟨Xmax⟩). The use of CIC method to measure the all-particle cosmic ray spectrum with IceTop in the range of PeV to EeV is discussed.This dissertation is divided into eight chapters. Chapter 1 is the introduction. Chapter 2 details the IceCube Neutrino Observatory. It describes the Digital Optical Module (DOM) and discusses how DAQ system, trigger/filter, and data transfer operate. IceTop, a surface component of the IceCube Neutrino Observatory, uses various calibration techniques. These calibrations are also discussed in this chapter. Chapter 3 describes the new two-station trigger and filter implemented to collect low energy cosmic rays. Chapter 4 discusses the simulation used for low energy spectrum analysis. Chapter 5 describes the reconstruction of air showers collected using two-station trigger/filter based on machine learning. Chapter 6 reports the result of all-particle cosmic ray spectrum using two-station events. The energy threshold using two-station events is lowered down to ~250 TeV. Chapter 7 details the constant intensity cut (CIC) method. This method is studied to increase the zenith range for energy spectrum and to use a zenith independent energy proxy for all-particle energy spectrum calculations. The final chapter, Chapter 8, summarizes the results and discusses possible future work.
Combined Blunt Aortic and Bronchial Injury Wong, Poo-Sing; Koirala, Ramesh R.; Lee, Chuen-Neng
The Annals of thoracic surgery,
12/2004, Volume:
78, Issue:
6
Journal Article
Peer reviewed
We report the case of a 29-year-old man with left blunt chest trauma resulting in an intimal tear of the proximal descending aorta, for which he underwent successful thoracic endovascular graft ...stenting. He subsequently developed progressive left lung collapse, and bronchoscopy revealed left bronchial disruption. A left thoracotomy with end-to-end anastomosis of the left bronchus was performed successfully. The literature from 6 other similar cases of concomitant aortic and bronchial injuries was reviewed.
Using IceTop, the surface component of the IceCube Neutrino Observatory, the all-particle cosmic ray energy spectrum has been determined above a few PeV. The measured energy spectrum leaves a gap of ...more than a decade in energy to direct measurements by balloon and satellite experiments. In this analysis, we lowered the energy threshold of IceTop to 250 TeV, narrowing the gap between IceTop and direct measurements. In order to collect lower energy events, we implemented a new trigger that uses four pairs of infill stations for which the separation between stations is less than 50 m, compared to 125 m for the main array. The new trigger collects data from the entire array for events with hits on at least one infill pair. The low-energy extension of the all-particle cosmic ray energy spectrum using these IceTop events is measured and is compared with the energy spectrum from HAWC and other experiments. Air shower simulations with two different hadronic interaction models, Sibyll 2.1 and QGSJetII-04, are used in this analysis and an energy spectrum for each model is produced. Both measured energy spectra show a bend around the knee region.
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