Self-association of the Shigella flexneri IcsA autotransporter protein

The IcsA autotransporter protein is a major virulence factor of the human intracellular pathogen Shigella flexneri. IcsA is distributed at the poles in the outer membrane (OM) of S. flexneri and interacts with components of the host actin-polymerization machinery to facilitate intracellular actin-based motility and subsequent cell-to-cell spreading of the bacterium. We sought to characterize the biochemical properties of IcsA in the bacterial OM. Chemical cross-linking data suggested that IcsA exists in a complex in the OM. Furthermore, reciprocal co-immunoprecipitation of differentially epitope-tagged IcsA proteins indicated that IcsA is able to self-associate. The identification of IcsA linker-insertion mutants that were negatively dominant provided genetic evidence of IcsA–IcsA interactions. From these results, we propose a model whereby IcsA self-association facilitates efficient actin-based motility.Kerrie L. May, Marcin Grabowicz, Steven W. Polyak and Renato Moron

The Hopf Algebra of Renormalization, Normal Coordinates and Kontsevich Deformation Quantization

Using normal coordinates in a Poincar\'e-Birkhoff-Witt basis for the Hopf algebra of renormalization in perturbative quantum field theory, we investigate the relation between the twisted antipode axiom in that formalism, the Birkhoff algebraic decomposition and the universal formula of Kontsevich for quantum deformation.Comment: 21 pages, 15 figure

Sums over Graphs and Integration over Discrete Groupoids

We show that sums over graphs such as appear in the theory of Feynman diagrams can be seen as integrals over discrete groupoids. From this point of view, basic combinatorial formulas of the theory of Feynman diagrams can be interpreted as pull-back or push-forward formulas for integrals over suitable groupoids.Comment: 27 pages, 4 eps figures; LaTeX2e; uses Xy-Pic. Some ambiguities fixed, and several proofs simplifie

Are You PEPped and PrEPped for Travel? Risk Mitigation of HIV Infection for Travelers

The HIV pandemic persists globally and travelers are at risk for infection by the Human Immunodeficiency Virus (HIV). While HIV-focused guidelines delineate risk stratification and mitigation strategies for people in their home communities, travel issues are not addressed. In this review, direct and indirect evidence on HIV risk among travelers is explored. The burgeoning practice of employing pre-exposure prophylaxis (PrEP) with anti-retroviral therapy in the non-travel setting is introduced, as well as the more established use of post-exposure prophylaxis (PEP). Challenges in applying these lessons to travelers are discussed, and a new guidelines process is scoped and recommended

Nucleotide triphosphate promiscuity in Mycobacterium tuberculosis dethiobiotin synthetase

Abstract not availableWanisa Salaemae, Min Y. Yap, Kate L. Wegener, Grant W. Booker, Matthew C.J. Wilce, Steven W. Polya

The Pure Virtual Braid Group Is Quadratic

If an augmented algebra K over Q is filtered by powers of its augmentation ideal I, the associated graded algebra grK need not in general be quadratic: although it is generated in degree 1, its relations may not be generated by homogeneous relations of degree 2. In this paper we give a sufficient criterion (called the PVH Criterion) for grK to be quadratic. When K is the group algebra of a group G, quadraticity is known to be equivalent to the existence of a (not necessarily homomorphic) universal finite type invariant for G. Thus the PVH Criterion also implies the existence of such a universal finite type invariant for the group G. We apply the PVH Criterion to the group algebra of the pure virtual braid group (also known as the quasi-triangular group), and show that the corresponding associated graded algebra is quadratic, and hence that these groups have a (not necessarily homomorphic) universal finite type invariant.Comment: 53 pages, 15 figures. Some clarifications added and inaccuracies corrected, reflecting suggestions made by the referee of the published version of the pape

Molecular-orbital-free algorithm for excited states in time-dependent perturbation theory

A non-linear conjugate gradient optimization scheme is used to obtain excitation energies within the Random Phase Approximation (RPA). The solutions to the RPA eigenvalue equation are located through a variational characterization using a modified Thouless functional, which is based upon an asymmetric Rayleigh quotient, in an orthogonalized atomic orbital representation. In this way, the computational bottleneck of calculating molecular orbitals is avoided. The variational space is reduced to the physically-relevant transitions by projections. The feasibility of an RPA implementation scaling linearly with system size, N, is investigated by monitoring convergence behavior with respect to the quality of initial guess and sensitivity to noise under thresholding, both for well- and ill-conditioned problems. The molecular- orbital-free algorithm is found to be robust and computationally efficient providing a first step toward a large-scale, reduced complexity calculation of time-dependent optical properties and linear response. The algorithm is extensible to other forms of time-dependent perturbation theory including, but not limited to, time-dependent Density Functional theory.Comment: 9 pages, 7 figure

ГЕПАТИТ А. СУЧАСНІ ОСОБЛИВОСТІ «СТАРОЇ ІНФЕКЦІЇ» У ЖИТЕЛІВ ЗАКАРПАТСЬКОЇ ОБЛАСТІ

Peculiarities of Hepatitis A (HA) manifestation on modern stage have been analyzed among the inhabitants of Zakarpatye region. It has been proved, that HA morbidity is still actual for the Zakarpatye region. Regional morbidity in 100 thousand inhabitants exceeds national figures. The activation of epidemic process happens each 3-6 years. Children have prevalence among the patients with HA. Children of age 5-14 years and adults 19-29 are more prone of being ill. Among children with HA males are more frequent. For the hepatitis A in children – jaundice forms of mild and moderate severity are prevalent, for adults – jaundice form of moderate severity. HA  has much severe course of the diseases in adults.Проаналізовано особливості проявів гепатиту А (ГА) у жителів Закарпатської області на сучасному етапі. Доведено, що захворювання на ГА продовжує залишатися актуальним для Закарпатської області. Захворюваність в області на 100 тис. населення знач­но перевершує загальнодержавні показники. Активація епідемічного процесу відбувається кожні 3-6 років. Серед хворих на ГА превалюють діти. Найчастіше хворіють діти віком 5-14 років та дорослі 19-29 років. Серед дітей більшість осіб чоловічої статі. Для ГА у дитячому віці характерним є жовтянична форма легкого і середнього ступенів тяжкості, для дорослих – жовтянична форма середнього ступеня. ГА перебігає тяжче у дорослому віці

Topological entropy of a stiff ring polymer and its connection to DNA knots

We discuss the entropy of a circular polymer under a topological constraint. We call it the {\it topological entropy} of the polymer, in short. A ring polymer does not change its topology (knot type) under any thermal fluctuations. Through numerical simulations using some knot invariants, we show that the topological entropy of a stiff ring polymer with a fixed knot is described by a scaling formula as a function of the thickness and length of the circular chain. The result is consistent with the viewpoint that for stiff polymers such as DNAs, the length and diameter of the chains should play a central role in their statistical and dynamical properties. Furthermore, we show that the new formula extends a known theoretical formula for DNA knots.Comment: 14pages,11figure