61 research outputs found
Calcium Influx Rescues Adenylate Cyclase-Hemolysin from Rapid Cell Membrane Removal and Enables Phagocyte Permeabilization by Toxin Pores
Bordetella adenylate cyclase toxin-hemolysin (CyaA) penetrates the cytoplasmic membrane of phagocytes and employs two distinct conformers to exert its multiple activities. One conformer forms cation-selective pores that permeabilize phagocyte membrane for efflux of cytosolic potassium. The other conformer conducts extracellular calcium ions across cytoplasmic membrane of cells, relocates into lipid rafts, translocates the adenylate cyclase enzyme (AC) domain into cells and converts cytosolic ATP to cAMP. We show that the calcium-conducting activity of CyaA controls the path and kinetics of endocytic removal of toxin pores from phagocyte membrane. The enzymatically inactive but calcium-conducting CyaA-AC− toxoid was endocytosed via a clathrin-dependent pathway. In contrast, a doubly mutated (E570K+E581P) toxoid, unable to conduct Ca2+ into cells, was rapidly internalized by membrane macropinocytosis, unless rescued by Ca2+ influx promoted in trans by ionomycin or intact toxoid. Moreover, a fully pore-forming CyaA-ΔAC hemolysin failed to permeabilize phagocytes, unless endocytic removal of its pores from cell membrane was decelerated through Ca2+ influx promoted by molecules locked in a Ca2+-conducting conformation by the 3D1 antibody. Inhibition of endocytosis also enabled the native B. pertussis-produced CyaA to induce lysis of J774A.1 macrophages at concentrations starting from 100 ng/ml. Hence, by mediating calcium influx into cells, the translocating conformer of CyaA controls the removal of bystander toxin pores from phagocyte membrane. This triggers a positive feedback loop of exacerbated cell permeabilization, where the efflux of cellular potassium yields further decreased toxin pore removal from cell membrane and this further enhances cell permeabilization and potassium efflux
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AIR FORCE SATELLITE CONTROL FACILITY ARCHITECTURE
International Telemetering Conference Proceedings / October 22-25, 1984 / Riviera Hotel, Las Vegas, NevadaThis paper presents an architectural overview of the Air Force Satellite Control Facility (AFSCF) with emphasis on the network’s Remote Tracking Stations (RTSs). The AFSCF originated twenty-five years ago, and has evolved into a global satellite service network. This worldwide network is composed of twelve RTSs, located at seven geographically dispersed locations, and a Satellite Test Center (STC) at Sunnyvale, California. The AFSCF provides real-time telemetry, tracking, and commanding (TT&C) service to Department of Defense (DoD) spacecraft and launch vehicles. In response to changing DoD space support requirements, the AFSCF and its RTSs have grown through expansion and modernization of their tracking, data processing, and communication capabilities. What follows is, then, a review of this network evolution; a description of today’s, stations, their capabilities and limitations; an introduction of planned improvements; and a view of what will be required for satellite service in the future.International Foundation for TelemeteringProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit http://www.telemetry.org/index.php/contact-us if you have questions about items in this collection
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The Air Force Satellite Control Facility
International Telemetering Conference Proceedings / October 14-16, 1980 / Bahia Hotel, San Diego, CaliforniaThe Air Force Satellite Control Facility (AFSCF) originated over twenty years ago, and has evolved into a global satellite support network. This global network includes seven Remote Tracking Stations (RTS's), support elements, and the Satellite Test Center (STC) located in Sunnyvale, California. The AFSCF provides real-time telemetry, tracking, and command support to Department of Defense (DOD) spacecraft and launch vehicles. Since its inception in response to changing DOD space support requirements, the SCF network has grown through expansion and modernization of its tracking, data processing, and communication capabilities. This paper discusses the past, the present, and projected AFSCF in support of the DOD space programs and including the Space Transportation System (STS).International Foundation for TelemeteringProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit http://www.telemetry.org/index.php/contact-us if you have questions about items in this collection
Vertical extrusion and horizontal spreading of orogenic lower crust: a key exhumation mechanism in large hot orogens?
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