The stochastic entry of enveloped viruses: Fusion vs. endocytosis

Viral infection requires the binding of receptors on the target cell membrane to glycoproteins, or ``spikes,'' on the viral membrane. The initial entry is usually classified as fusogenic or endocytotic. However, binding of viral spikes to cell surface receptors not only initiates the viral adhesion and the wrapping process necessary for internalization, but can simultaneously initiate direct fusion with the cell membrane. Both fusion and internalization have been observed to be viable pathways for many viruses. We develop a stochastic model for viral entry that incorporates a competition between receptor mediated fusion and endocytosis. The relative probabilities of fusion and endocytosis of a virus particle initially nonspecifically adsorbed on the host cell membrane are computed as functions of receptor concentration, binding strength, and number of spikes. We find different parameter regimes where the entry pathway probabilities can be analytically expressed. Experimental tests of our mechanistic hypotheses are proposed and discussed.Comment: 7 pages, 6 figure

Collective dynamics in noble-gas and other very simple classical fluids

Rare gases and their liquids are the simplest systems to study for accurate investigations of the collective dynamics of fluid matter. Much work has been done using different spectroscopic techniques, moleculardynamics simulations, and theoretical developments, in order to gain insight into the microscopic processes involved, in particular, in the propagation of acoustic excitations in gases and liquids. Here we briefly review the interpretation schemes currently applied to the characterization of such excitations, and recall a few results obtained from the analysis of rare-gas fluids and other very simple systems.Iнертнi гази та їхнi рiдини є найпростiшими системами для точних дослiджень колективної динамiки плинiв. Було пророблено значну роботу з використанням рiзноманiтних спектроскопiчних методик, моделювання методом молекулярної динамiки та теоретичних розробок для розумiння мiкроскопiчних процесiв, що приймають участь у поширеннi звукових збуджень у газах та рiдинах. Ми подаємо короткий огляд iнтерпретацiйних схем, що застосовуються для опису таких збуджень, та нагадуємо декiлька результатiв, отриманих iз аналiзу плинiв iнертних газiв та iнших дуже простих систем

Effects of three-body interactions on the structure and thermodynamics of liquid krypton

Large-scale molecular dynamics simulations are performed to predict the structural and thermodynamic properties of liquid krypton using a potential energy function based on the two-body potential of Aziz and Slaman plus the triple-dipole Axilrod-Teller (AT) potential. By varying the strength of the AT potential we study the influence of three-body contribution beyond the triple-dipole dispersion. It is seen that the AT potential gives an overall good description of liquid Kr, though other contributions such as higher order three-body dispersion and exchange terms cannot be ignored.Comment: 11 pages, 3 figures, LaTeX, to appear in J. Chem. Phy

Assessment of Streptococcus pneumoniae pilus islet-1 prevalence in carried and transmitted isolates from mother–infant pairs on the Thailand–Burma border

AbstractStreptococcus pneumoniae pilus islet-1 (PI–1)-encoded pilus enhances in vitro adhesion to the respiratory epithelium and may contribute to pneumococcal nasopharyngeal colonization and transmission. The pilus subunits are regarded as potential protein vaccine candidates. In this study, we sought to determine PI–1 prevalence in carried pneumococcal isolates and explore its relationship with transmissibility or carriage duration. We studied 896 pneumococcal isolates collected during a longitudinal carriage study that included monthly nasopharyngeal swabbing of 234 infants and their mothers between the ages of 1 and 24 months. These were cultured according to the WHO pneumococcal carriage detection protocol. PI-1 PCR and genotyping by multilocus sequence typing were performed on isolates chosen according to specific carriage and transmission definitions. Overall, 35.2% of the isolates were PI-1-positive, but PI-1 presence was restricted to ten of the 34 serotypes studied and was most frequently associated with serotypes 19F and 23F; 47.5% of transmitted and 43.3% of non-transmitted isolates were PI-1-positive (OR 1.2; 95% CI 0.8-1.7; p 0.4). The duration of first-ever infant pneumococcal carriage was significantly longer with PI-1-positive organisms, but this difference was not significant at the individual serotype level. In conclusion, PI-1 is commonly found in pneumococcal carriage isolates, but does not appear to be associated with pneumococcal transmissibility or carriage duration

Pneumococcal Pili Are Composed of Protofilaments Exposing Adhesive Clusters of Rrg A

Pili have been identified on the cell surface of Streptococcus pneumoniae, a major cause of morbidity and mortality worldwide. In contrast to Gram-negative bacteria, little is known about the structure of native pili in Gram-positive species and their role in pathogenicity. Triple immunoelectron microscopy of the elongated structure showed that purified pili contained RrgB as the major compound, followed by clustered RrgA and individual RrgC molecules on the pilus surface. The arrangement of gold particles displayed a uniform distribution of anti-RrgB antibodies along the whole pilus, forming a backbone structure. Antibodies against RrgA were found along the filament as particulate aggregates of 2–3 units, often co-localised with single RrgC subunits. Structural analysis using cryo electron microscopy and data obtained from freeze drying/metal shadowing technique showed that pili are oligomeric appendages formed by at least two protofilaments arranged in a coiled-coil, compact superstructure of various diameters. Using extracellular matrix proteins in an enzyme-linked immunosorbent assay, ancillary RrgA was identified as the major adhesin of the pilus. Combining the structural and functional data, a model emerges where the pilus RrgB backbone serves as a carrier for surface located adhesive clusters of RrgA that facilitates the interaction with the host

Implementation of the Hierarchical Reference Theory for simple one-component fluids

Combining renormalization group theoretical ideas with the integral equation approach to fluid structure and thermodynamics, the Hierarchical Reference Theory is known to be successful even in the vicinity of the critical point and for sub-critical temperatures. We here present a software package independent of earlier programs for the application of this theory to simple fluids composed of particles interacting via spherically symmetrical pair potentials, restricting ourselves to hard sphere reference systems. Using the hard-core Yukawa potential with z=1.8/sigma for illustration, we discuss our implementation and the results it yields, paying special attention to the core condition and emphasizing the decoupling assumption's role.Comment: RevTeX, 16 pages, 2 figures. Minor changes, published versio

Neutron Brillouin scattering and ab initio simulation study of the collective dynamics of liquid silver

Producción CientíficaWe present a thorough investigation of the collective dynamics of liquid Ag combining neutron Brillouin scattering and ab initio molecular dynamics (AIMD) determinations of the dynamic structure factor S(Q,ω). The main scope of this work is not only to provide experimental results for some important dynamical properties of this liquid metal in the wave-vector range 4<Q<16nm−1, but also to inquire about the scarce detectability of shear waves apparently characterizing two elements of group IB, differently from other metals. In fact, as in the case of Au, a transverse-like dynamics is not deducible from the experimental S(Q,ω) of Ag, despite the indisputable quality of the neutron data collected on the BRISP spectrometer at the Institut Laue Langevin in Grenoble. However, the significant agreement between experiment and AIMD calculations allowed for an in-depth study of the simulated S(Q,ω) in a Q range overlapping and extending the experimental one. A multimode analysis, already proven very successful in the description of various dynamical properties of fluid systems, is shown to be extremely effective also to analyze the intermediate scattering function predicted by AIMD at the various Q values, and eventually enables a reliable determination of both longitudinal and transverse branches in the dispersion curve of this liquid. Throughout the paper we highlight the importance of referring to theoretically well-founded models for S(Q,ω) and of imposing physical constraints in a fit-based analysis: These ensure that the used models obey fundamental properties of the dynamic structure factor.Ministero dell’Istruzione dell’Università e della Ricerca Italiano (grant PRIN2017-2017Z55KCW)Ministerio de Economía, Industria y Competitividad (project PGC2018-093745-B-I00)Junta de Castilla y León (project VA124G18

Un discurso, todos los discursos : literatura y transdiscursvidad II

Desde hace varias décadas, la teoría literaria viene desarrollando en profundidad la noción de texto literario como objeto social. De este axioma se desprende, entre otros corolarios, que es necesario considerarlo en el interior de la red de relaciones que establece con otros textos y con los diferentes discursos, artísticos o no, que la atraviesan: la literatura representa fenómenos históricos, políticos y culturales y en ella se entrecruzan los diversos discursos producidos por las prácticas sociales de un determinado tiempo y lugar. Se impone, entonces, el análisis de las relaciones discursivas entre diversas esferas de la cultura