Rates of seropositivity for Toxoplasma gondii antibodies in polar bears and marine mammals around Svalbard

Little is known about the prevalence of the parasite Toxoplasma gondii in the arctic marine food chain of Svalbard, Norway. In this study, plasma samples were analyzed for T. gondii antibodies using a direct agglutination test. Antibody prevalence was 45.6% among polar bears (Ursus maritimus), 18.7% among ringed seals (Pusa hispida) and 66.7% among adult bearded seals (Erignathus barbatus) from Svalbard, but no sign of antibodies were found in bearded seal pups, harbour seals (Phoca vitulina), white whales (Delphinapterus leucas) or narwhals (Monodon monoceros) from the same area. Prevalence was significantly higher in male polar bears (52.3%) compared with females (39.3%), likely due to dietary differences between the sexes. Compared to an earlier study, T. gondii prevalence in polar bears has doubled in the past decade. Consistently, an earlier study on ringed seals did not detect T. gondii. The high recent prevalence in polar bears, ringed seals and bearded seals could be caused by an increase in the number or survivorship of oocysts being transported via the North Atlantic Current to Svalbard from southern latitudes. Warmer water temperatures have led to influxes of temperate marine invertebrate filter-feeders that could be vectors for oocysts and warmer water is also likely to favour higher survivorship of oocycts. However, a more diverse than normal array of migratory birds in the Archipelago recently, as well as a marked increase in cruise-ship and other human traffic are also potential sources of T. gondii.

Physiography of the Orca Seamount in the Bransfield Strait, Antarctic Peninsula

Extract from related chapter 5.5.2 in reference: The Orca Seamount was discovered in the central basin of the Bransfield Strait around the posit 62��26'S and 58��24'W on the west side of the Antarctic Peninsula, the most western area of the south polar continent. Through the discovery was made known in 1987, it was only during three bathymetric surveys with high resolution fan echosounders between 1993 and 1995 that the character and complete shape of a remarkable volcano seamount became evident. The data acquisition and processing revealed a spectacular crater of 350 m depth. The relative hight of this 3 km wide "caldera" rim is 550 m with a basal diameter of the seamount cone of 11 km. Its flanks are about 15�� steep but in some places the slope reaches up to 36��. The nearly circular shape of the Orca edifice spreads outh with several pronounced spurs, trending parallel to the basin axis in a northeast-southwest direction. The Bransfield Strait is a trough-shaped basin of 400 km length and 2 km depth between the South Shetland Island Arc and the Antarctic Peninsula, formed by rifting behind the islands. The separation of the South Shetland island chain from the peninsula began possibly several million years ago. The active rifting is still going on however, and has caused recent earthquakes and volcanism along the Bransfield Strait. The Strait hosts a chain of submerged seamounts of volcanic origin with the presently inactive Ora Seamount as the most spectacular one. The South Shelfand Island owe their existence to a subduction related volcanism which is perhaps 5-10 times older than the age of Orca and the other seamounts along the central basin of the Bransfield Strait.

Grain-size distribution, sedimentation rate and x-ray fluorescence data of four sediment cores off the Senegal River estuary

Fine-grained sediment depocenters on continental shelves are of increased scientific interest since they record environmental changes sensitively. A north-south elongated mud depocenter extends along the Senegalese coast in mid-shelf position. Shallow-acoustic profiling was carried out to determine extent, geometry and internal structures of this sedimentary body. In addition, four sediment cores were retrieved with the main aim to identify how paleoclimatic signals and coastal changes have controlled the formation of this mud depocenter. A general paleoclimatic pattern in terms of fluvial input appears to be recorded in this depositional archive. Intervals characterized by high terrigenous input, high sedimentation rates and fine grain sizes occur roughly contemporaneously in all cores and are interpreted as corresponding to intensified river discharge related to more humid conditions in the hinterland. From 2750 to 1900 and from 1000 to 700 cal a BP, wetter conditions are recorded off Senegal, an observation which is in accordance with other records from NW-Africa. Nevertheless, the three employed proxies (sedimentation rate, grain size and elemental distribution) do not always display consistent inter-core patterns. Major differences between the individual core records are attributed to sediment remobilization which was linked to local hydrographic variations as well as reorganizations of the coastal system. The Senegal mud belt is a layered inhomogeneous sedimentary body deposited on an irregular erosive surface. Early Holocene deceleration in the rate of the sea-level rise could have enabled initial mud deposition on the shelf. These favorable conditions for mud deposition occur coevally with a humid period over NW-Africa, thus, high river discharge. Sedimentation started preferentially in the northern areas of the mud belt. During mid-Holocene, a marine incursion led to the formation of an embayment. Afterwards, sedimentation in the north was interrupted in association with a remarkable southward shift in the location of the active depocenter as it is reflected by the sedimentary architecture and confirmed by radiocarbon dates. These sub-recent shifts in depocenters location are caused by migrations of the Senegal River mouth. During late Holocene times, the weakening of river discharge allowed the longshore currents to build up a chain of beach barriers which have forced the river mouth to shift southwards.

The counteractive effect of the sensor housing on the unit sensitivity across a series of dynamic temperature profiles.

The advantages of wireless sensing implemented on the cold chain of fresh products are well known. These sensor systems consist of a combination of delicate internal electronic circuitry enclosed in a special housing unit. Manufacturers however are presented with the challenge that the housing required to withstand the harsh environment in which the sensors are being used all too often take from the functionality of the sensor. Therefore the target of this study is to determine the dynamic behavior and the counteractive effects of the sensor housing on temperature recording accuracy in the wireless nodes of Wireless Sensor Network (WSN) and Radio Frequency Identification (RFID) semi-passive tags. Two kind of semi-passive Turbo Tags were used (T700 and T702-B), which consisted of sensors with and without a cover, and two kind of WSN nodes, IRIS (sensors Intersema and Sensirion soldered in the motherboard) and NLAZA (Sensirion in a cable and soldered to the motherboard). To recreate the temperature profiles the devices were rotated between a cold room(5 ��C) through a ambient room(23 ��C) to a heated environment (35��C) and vice versa. Analysis revealed the differences between housing and no housing are 308.22s to 21.99s respectively in the step from 5 to 35 ��C. As is demonstrated in these experiments the influence of the housing significantly hinders sensor accuracy.

Design and optimization of optical, fiber based PSK demodulators for high-bit-rate optical networks

El objetivo principal de esta tesis ha sido el dise��o y la optimizaci��n de receptores implementados con fibra ��ptica, para ser usados en redes ��pticas de alta velocidad que empleen formatos de modulaci��n de fase. En los ��ltimos a��os, los formatos de modulaci��n de fase (Phase Shift keying, PSK) han captado gran atenci��n debido a la mejora de sus prestaciones respecto a los formatos de modulaci��n convencionales. Principalmente, presentan una mejora de la eficiencia espectral y una mayor tolerancia a la degradaci��n de la se��al causada por la dispersi��n crom��tica, la dispersi��n por modo de polarizaci��n y los efectos no-lineales en la fibra ��ptica. En este trabajo, se analizan en detalle los formatos PSK, incluyendo sus variantes de modulaci��n de fase diferencial (Differential Phase Shift Keying, DPSK), en cuadratura (Differential Quadrature Phase Shift Keying, DQPSK) y multiplexaci��n en polarizaci��n (Polarization Multiplexing Differential Quadrature Phase Shift Keying, PM-DQPSK), con la finalidad de dise��ar y optimizar los receptores que permita su demodulaci��n. Para ello, se han analizado y desarrollado nuevas estructuras que ofrecen una mejora en las prestaciones del receptor y una reducci��n de coste comparadas con las actualmente disponibles. Para la demodulaci��n de se��ales DPSK, en esta tesis, se proponen dos nuevos receptores basados en un interfer��metro en l��nea Mach-Zehnder (MZI) implementado con tecnolog��a todo-fibra. El principio de funcionamiento de los MZI todo-fibra propuestos se asienta en la interferencia modal que se produce en una fibra multimodo (MMF) cuando se situada entre dos monomodo (SMF). Este tipo de configuraci��n (monomodo-multimodo-monomodo, SMS) presenta un buen ratio de extinci��n interferente si la potencia acoplada en la fibra multimodo se reparte, principal y equitativamente, entre dos modos dominantes. Con este objetivo, se han estudiado y demostrado tanto te��rica como experimentalmente dos nuevas estructuras SMS que mejoran el ratio de extinci��n. Una de las propuestas se basa en emplear una fibra multimodo de ��ndice gradual cuyo perfil del ��ndice de refracci��n presenta un hundimiento en su zona central. La otra consiste en una estructura SMS con las fibras desalineadas y donde la fibra multimodo es una fibra de ��ndice gradual convencional. Para las dos estructuras, mediante el an��lisis te��rico desarrollado, se ha demostrado que el 80 ��� 90% de la potencia de entrada se acopla a los dos modos dominantes de la fibra multimodo y se consigue una diferencia inferior al 10% entre ellos. Tambi��n se ha demostrado experimentalmente que se puede obtener un ratio de extinci��n de al menos 12 dB. Con el objeto de demostrar la capacidad de estas estructuras para ser empleadas como demoduladores de se��ales DPSK, se han realizado numerosas simulaciones de un sistema de transmisi��n ��ptico completo y se ha analizado la calidad del receptor bajo diferentes perspectivas, tales como la sensibilidad, la tolerancia a un filtrado ��ptico severo o la tolerancia a las dispersiones crom��tica y por modo de polarizaci��n. En todos los casos se ha concluido que los receptores propuestos presentan rendimientos comparables a los obtenidos con receptores convencionales. En esta tesis, tambi��n se presenta un dise��o alternativo para la implementaci��n de un receptor DQPSK, basado en el uso de una fibra mantenedora de la polarizaci��n (PMF). A trav��s del an��lisi te��rico y del desarrollo de simulaciones num��ricas, se ha demostrado que el receptor DQPSK propuesto presenta prestaciones similares a los convencionales. Para complementar el trabajo realizado sobre el receptor DQPSK basado en PMF, se ha extendido el estudio de su principio de demodulaci��n con el objeto de demodular se��ales PM-DQPSK, obteniendo como resultado la propuesta de una nueva estructura de demodulaci��n. El receptor PM-DQPSK propuesto se basa en la estructura conjunta de una ��nica l��nea de retardo junto con un rotador de polarizaci��n. Se ha analizado la calidad de los receptores DQPSK y PM-DQPSK bajo diferentes perspectivas, tales como la sensibilidad, la tolerancia a un filtrado ��ptico severo, la tolerancia a las dispersiones crom��tica y por modo de polarizaci��n o su comportamiento bajo condiciones no-ideales. En comparaci��n con los receptores convencionales, nuestra propuesta exhibe prestaciones similares y adem��s permite un dise��o m��s simple que redunda en un coste potencialmente menor. En las redes de comunicaciones ��pticas actuales se utiliza la tecnolog��a de multimplexaci��n en longitud de onda (WDM) que obliga al uso de filtros ��pticos con bandas de paso lo m��s estrechas posibles y a emplear una serie de dispositivos que incorporan filtros en su arquitectura, tales como los multiplexores, demultiplexores, ROADMs, conmutadores y OXCs. Todos estos dispositivos conectados entre s�� son equivalentes a una cadena de filtros cuyo ancho de banda se va haciendo cada vez m��s estrecho, llegando a distorsionar la forma de onda de las se��ales. Por esto, adem��s de analizar el impacto del filtrado ��ptico en las se��ales de 40 Gbps DQPSK y 100 Gbps PM-DQPSK, este trabajo de tesis se completa estudiando qu�� tipo de filtro ��ptico minimiza las degradaciones causadas en la se��al y analizando el n��mero m��ximo de filtros concatenados que permiten mantener la calidad requerida al sistema. Se han estudiado y simulado cuatro tipos de filtros ��pticos;Butterworth, Bessel, FBG y F-P. ABSTRACT The objective of this thesis is the design and optimization of optical fiber-based phase shift keying (PSK) demodulators for high-bit-rate optical networks. PSK modulation formats have attracted significant attention in recent years, because of the better performance with respect to conventional modulation formats. Principally, PSK signals can improve spectrum efficiency and tolerate more signal degradation caused by chromatic dispersion, polarization mode dispersion and nonlinearities in the fiber. In this work, many PSK formats were analyzed in detail, including the variants of differential phase modulation (Differential Phase Shift Keying, DPSK), in quadrature (Differential Quadrature Phase Shift Keying, DQPSK) and polarization multiplexing (Polarization Multiplexing Differential Quadrature Phase Shift Keying, PM-DQPSK), in order to design and optimize receivers enabling demodulations. Therefore, novel structures, which offer good receiver performances and a reduction in cost compared to the current structures, have been analyzed and developed. Two novel receivers based on an all-fiber in-line Mach-Zehnder interferometer (MZI) were proposed for DPSK signal demodulation in this thesis. The operating principle of the all-fiber MZI is based on the modal interference that occurs in a multimode fiber (MMF) when it is located between two single-mode fibers (SMFs). This type of configuration (Single-mode-multimode-single-mode, SMS) can provide a good extinction ratio if the incoming power from the SMF could be coupled equally into two dominant modes excited in the MMF. In order to improve the interference extinction ratio, two novel SMS structures have been studied and demonstrated, theoretically and experimentally. One of the two proposed MZIs is based on a graded-index multimode fiber (MMF) with a central dip in the index profile, located between two single-mode fibers (SMFs). The other one is based on a conventional graded-index MMF mismatch spliced between two SMFs. Theoretical analysis has shown that, in these two schemes, 80 ��� 90% of the incoming power can be coupled into the two dominant modes exited in the MMF, and the power difference between them is only ~10%. Experimental results show that interference extinction ratio of 12 dB could be obtained. In order to demonstrate the capacity of these two structures for use as DPSK signal demodulators, numerical simulations in a completed optical transmission system have been carried out, and the receiver quality has been analyzed under different perspectives, such as sensitivity, tolerance to severe optical filtering or tolerance to chromatic and polarization mode dispersion. In all cases, from the simulation results we can conclude that the two proposed receivers can provide performances comparable to conventional ones. In this thesis, an alternative design for the implementation of a DQPSK receiver, which is based on a polarization maintaining fiber (PMF), was also presented. To complement the work made for the PMF-based DQPSK receiver, the study of the demodulation principle has been extended to demodulate PM-DQPSK signals, resulting in the proposal of a novel demodulation structure. The proposed PM-DQPSK receiver is based on only one delay line and a polarization rotator. The quality of the proposed DQPSK and PM-DQPSK receivers under different perspectives, such as sensitivity, tolerance to severe optical filtering, tolerance to chromatic dispersion and polarization mode dispersion, or behavior under non-ideal conditions. Compared with the conventional receivers, our proposals exhibit similar performances but allow a simpler design which can potentially reduce the cost. The wavelength division multiplexing (WDM) technology used in current optical communications networks requires the use of optical filters with a passband as narrow as possible, and the use of a series of devices that incorporate filters in their architecture, such as multiplexers, demultiplexers, switches, reconfigurable add-drop multiplexers (ROADMs) and optical cross-connects (OXCs). All these devices connected together are equivalent to a chain of filters whose bandwidth becomes increasingly narrow, resulting in distortion to the waveform of the signals. Therefore, in addition to analyzing the impact of optical filtering on signal of 40 Gbps DQPSK and 100 Gbps PM-DQPSK, we study which kind of optical filter minimizes the signal degradation and analyze the maximum number of concatenated filters for maintaining the required quality of the system. Four types of optical filters, including Butterworth, Bessel, FBG and FP, have studied and simulated.

Definici��n de los procedimientos e indicadores de la cadena de custodia de la industria de pasta y papel vinculados a la normativa ISO 9000/14000

En el trabajo se ha reflejado la g��nesis del t��rmino ���desarrollo sostenible��� y la preocupaci��n social y de los gobiernos hacia la sostenibilidad de los recursos, generando una pol��tica forestal a escala internacional, cuyo hito inicial desempe��a la Cumbre de Rio y otros procesos, donde surge el t��rmino ���sostenibilidad��� - procesos gubernamentales que ponen su atenci��n en los bosques,entre ellos el Proceso paneuropeo del que emanan los Criterios e indicadores de la gesti��n forestal sostenible, as�� como otros foros donde aparece la vinculaci��n entre los productos y la sostenibilidad de los bosques de donde proceden. A partir de esos conceptos aparecen los sistemas de certificaci��n, primero FSC, promovido por las ONG ambientalistas, y en respuesta a ello, el sistema PEFC de los propietarios forestales privados con las industrias forestales. En su introducci��n, el trabajo recoge como surge y evoluciona esta preocupaci��n y como se sucede y desarrollan los sistemas de certificaci��n en Espa��a, orientados tanto a la superficie forestal como a sus productos derivados. Tratando de ser una herramienta t��cnica, en estos ��ltimos quince a��os, se han ido planteando metodolog��as y propuestas t��cnicas que puedan garantizar el origen sostenible del bosque de donde procede la materia prima. Aunque la persistencia de la masa forestal como t��rmino tiene importancia, no considera numerosos aspectos incluidos en el concepto ���gesti��n forestal sostenible���. El trabajo manifiesta qu�� es y c��mo se origina la Gesti��n Forestal Sostenible y muy ligado con ello, el origen de la certificaci��n como herramienta, explicando c��mo se incardina la certificaci��n forestal espa��ola con las estructuras internacionales y se construyen nuevas estructuras a escala espa��ola y auton��mica. Se expone el dominio y alcance t��cnico de la certificaci��n, sus inicios y un an��lisis de la diversidad de sistemas y etiquetas existentes -como ha ido evolucionando a escala internacional y nacional, por sistemas, sectores y continentes, con especial atenci��n en Espa��a, recopilando lo sucedido relevante para el sector forestal, industrias forestales y sistemas de certificaci��n en los a��os de estudio de elaboraci��n de la tesis. Se refleja la relevancia que adquiere la certificaci��n forestal y de la cadena de custodia para la industria del papel, tanto por las regulaciones, normativas y legislaci��n que involucran al producto derivado del bosque como por ser herramienta que enlaza el bosque sostenible con el consumidor. La aplicaci��n de todas esas especificaciones t��cnicas que muestran la sostenibilidad del bosque y al trazabilidad en el proceso productivo comporta una carga administrativa de recopilaci��n de informaci��n, de control para el seguimiento asociado con los registros necesarios, y de archivo de documentos, conforme a las exigencias que plantean los sistemas de certificaci��n forestal. Por tanto, es importante definir un m��todo y procedimientos gen��ricos para los correspondientes sistemas de gesti��n preexistentes en las empresas del sector de pasta y papel (de calidad/ de medio ambiente/integrados), para implantar un Sistema de Cadena de Custodia gen��rico (com��n a FSC y PEFC) en una instalaci��n de celulosa y papel y un sistema de diligencia debida. Para ello, ha sido necesario analizar la l��nea de producci��n y establecer los puntos de su diagrama en los que se requiere el control de la trazabilidad, puntos en los que se procede al seguimiento y registro de la materia prima, materia semielaborada y producto, y de ah�� proceder a redactar o retocar los procedimientos de gesti��n calidad/ medioambiental, en su caso, para incluir los campos de registro. Seg��n determinen los procedimientos, se efectuar�� un seguimiento y registro de los, derivados que configuran una caracter��stica y se determinar�� una serie de indicadores del sistema de trazabilidad de la madera en la industria de celulosa y papel, es decir, un conjunto de par��metros cuantitativos y descriptivos, sujetos al seguimiento de forma peri��dica, que muestren el cambio y permitan observar la evaluaci��n y control del Sistema de Cadena de Custodia. Adem��s de asegurar la trazabilidad de la madera y fibra en la industria de pasta y papel y con ello la sostenibilidad del bosque del que procede, se avalar�� la legalidad de los aprovechamientos que proporcionan ese recurso maderable, cumpliendo as�� no s��lo la legislaci��n vigente sino tambi��n ambos sistemas de certificaci��n FSC y PEFC. El sistema de cadena de custodia de la pasta y papel se caracteriza por los indicadores de seguimiento que permite el control de la trazabilidad. ABSTRACT This paper traces the origins of the term ���Sustainable Development��� and of both citizen and institutional concern for the sustainability of resources, leading to the enactment of a forestry policy at international level, of which the initial milestones are the Rio Summit and other processes in which the term ���Sustainability��� was born. Those forestfocused institutional initiatives include the pan-European process that led to the publication of Sustainable Forest Management Criteria and Indicators, and other forums that highlight the link between finished wood-based products and the sustainability of the forests from which that wood is sourced. Those concepts were the culture in which forest certification systems were engendered, first FSC, promoted by environmental NGOs, and subsequently PEFC, fostered in response to FSC by private forest owners and forest-based industries. In its Introduction, this paper looks at how such concern arose and has evolved and how certification systems came into existence in Spain and developed to encompass both forest lands and forest-based products. As part of a mission to provide an applicable technical tool, new methodologies and technical proposals have been put forward over the past fifteen years aimed at guaranteeing the sustainable origin of the forest from which raw material is sourced. Although the maintenance of forest stands as a term in its own right is important, it does not take many of the aspects included in the concept of ���sustainable forest management��� into account. This thesis describes what SFM is and how it was born, underlying the close link between SFM and the origin of certification as a tool, explaining how Spanish forest certification is embodied in international structures, while new structures are built here in Spain on both the national and regional scale. This work also details the domain and scope of forest certification from the technical standpoint, explains its beginnings, and assesses the various systems and labels that exist - how certification has evolved internationally and nationally across systems, sectors and continents, with special emphasis on Spain. It provides a compilation of events relevant to forestry, forest industries and forest certification systems that have taken place during the years this thesis has been in preparation. It reflects on the relevance that forest and chain of custody certification holds for the paper industry, in view not only of the regulations, policies and legislation that affect forest-based products but also of its role as a tool that bonds the sustainable forest with the consumer. Implementing the range of technical specifications to demonstrate forest sustainability and traceability throughout the production process entails the administrative burden of collecting information and providing controls to process the relevant records and documents to be kept on file in compliance with the requirements made by forest certification schemes. It is therefore important to define a generic method, together with its relevant procedures,that fits the management systems (quality / environmental / integrated)existing today in pulp and paper companies, in order to implement a generic Chain of Custody scheme (common to FSC and PEFC) in a pulp and paper mill, and a due diligence system. To achieve that, it has first been necessary to analyse the production line and establish points along the route where traceabilitycontrols need to be implemented and points where raw material, semi-finished goods and end products should be monitored and recorded. Subsequently, the procedures in quality / environmental management systems need to be drafted or amended as required to include fields that reflect those records. As required by the procedures, forest-based products that have a specific characteristic shall be monitored and recorded, and a number of indicators identified in the traceability system of wood for pulp & paper, i.e.createa set of quantitative and descriptive parameters subject to regular monitoringthat reveal changes and enable the Chain of Custody system to be assessed and controlled. In addition to ensuring the traceability of wood and fibre in the pulp and paper industry -and so the sustainability of the forest from which it is sourced -, the legality of the harvesting that produces that timber will also be enhanced, thus fulfilling not only the law but also both FSC and PEFC certification schemes. The chain of custody system for pulp and paper is characterised by monitoring indicators that enable traceability to be controlled.

Food market analysis: a case study of the Glocal methodology in the Dominican Republic

The present paper provides an insight into the food value chain of three specific sectors (fruit and vegetables, poultry and rice) in the Dominican Republic. The Glocal methodology used for the study combines a global view with local conditions and thus it can be applied to food markets. Each of these food chains is analyzed by following traditional industrial organization theory, based on structure, conduct and performance. Regarding the specific case of the Dominican Republic, different sources of information are used to analyze the weaknesses of the studied chains, including direct interviews. The food value chains of fruit and vegetables, poultry and rice in the Dominican Republic show a lack of structure and they are undergoing changes; however, they also have great opportunities to improve efficiency by making some changes.

A mutant of Mycobacterium smegmatis defective in the biosynthesis of mycolic acids accumulates meromycolates

Mycolic acids are a major constituent of the mycobacterial cell wall, and they form an effective permeability barrier to protect mycobacteria from antimicrobial agents. Although the chemical structures of mycolic acids are well established, little is known on their biosynthesis. We have isolated a mycolate-deficient mutant strain of Mycobacterium smegmatis mc2-155 by chemical mutagenesis followed by screening for increased sensitivity to novobiocin. This mutant also was hypersensitive to other hydrophobic compounds such as crystal violet, rifampicin, and erythromycin. Entry of hydrophobic probes into mutant cells occurred much more rapidly than that into the wild-type cells. HPLC and TLC analysis of fatty acid composition after saponification showed that the mutant failed to synthesize full-length mycolic acids. Instead, it accumulated a series of long-chain fatty acids, which were not detected in the wild-type strain. Analysis by 1H NMR, electrospray and electron impact mass spectroscopy, and permanganate cleavage of double bonds showed that these compounds corresponded to the incomplete meromycolate chain of mycolic acids, except for the presence of a ��-hydroxyl group. This direct identification of meromycolates as precursors of mycolic acids provides a strong support for the previously proposed pathway for mycolic acid biosynthesis involving the separate synthesis of meromycolate chain and the ��-branch of mycolic acids, followed by the joining of these two branches.

The structure of the two amino-terminal domains of human ICAM-1 suggests how it functions as a rhinovirus receptor and as an LFA-1 integrin ligand

The normal function of human intercellular adhesion molecule-1 (ICAM-1) is to provide adhesion between endothelial cells and leukocytes after injury or stress. ICAM-1 binds to leukocyte function-associated antigen (LFA-1) or macrophage-1 antigen (Mac-1). However, ICAM-1 is also used as a receptor by the major group of human rhinoviruses and is a catalyst for the subsequent viral uncoating during cell entry. The three-dimensional atomic structure of the two amino-terminal domains (D1 and D2) of ICAM-1 has been determined to 2.2-��� resolution and fitted into a cryoelectron microscopy reconstruction of a rhinovirus���ICAM-1 complex. Rhinovirus attachment is confined to the BC, CD, DE, and FG loops of the amino-terminal Ig-like domain (D1) at the end distal to the cellular membrane. The loops are considerably different in structure to those of human ICAM-2 or murine ICAM-1, which do not bind rhinoviruses. There are extensive charge interactions between ICAM-1 and human rhinoviruses, which are mostly conserved in both major and minor receptor groups of rhinoviruses. The interaction of ICAMs with LFA-1 is known to be mediated by a divalent cation bound to the insertion (I)-domain on the �� chain of LFA-1 and the carboxyl group of a conserved glutamic acid residue on ICAMs. Domain D1 has been docked with the known structure of the I-domain. The resultant model is consistent with mutational data and provides a structural framework for the adhesion between these molecules.

Receptor-associated constitutive protein tyrosine phosphatase activity controls the kinase function of���JAK1

Exposure of cells to protein tyrosine phosphatase (PTP) inhibitors causes an increase in the phosphotyrosine content of many cellular proteins. However, the level at which the primary signaling event is affected is still unclear. We show that Jaks are activated by tyrosine phosphorylation in cells that are briefly exposed to the PTP inhibitor pervanadate (PV), resulting in tyrosine phosphorylation and functional activation of Stat6 (in addition to other Stats). Mutant cell lines that lack Jak1 activity fail to support PV-mediated [or interleukin 4 (IL-4)-dependent] activation of Stat6 but can be rescued by complementation with functional Jak1. The docking sites for both Jak1 and Stat6 reside in the cytoplasmic domain of the IL-4 receptor ��-chain (IL-4R��). The glioblastoma-derived cell lines T98G, GRE, and M007, which do not express the IL-4R�� chain, fail to support Stat6 activation in response to either IL-4 or PV. Complementation of T98G cells with the IL-4R�� restores both PV-mediated and IL-4-dependent Stat6 activation. Murine L929 cells, which do not express the �� common chain of the IL-4 receptor, support PV-mediated but not IL-4-dependent Stat6 activation. Thus, Stat6 activation by PV is an IL-4R��-mediated, Jak1-dependent event that is independent of receptor dimerization. We propose that receptor-associated constitutive PTP activity functions to down-regulate persistent, receptor-linked kinase activity. Inhibition or deletion of PTP activity results in constitutive activation of cytokine signaling pathways.

Demonstration of a novel circulating anti-prostacyclin receptor���antibody

Although coronary artery disease (CAD) is appreciated to be accelerated in patients with chronic spinal cord injury (SCI), the underlying mechanism of CAD in SCI remains obscure. We have recently shown that platelets from subjects with SCI develop resistance to the inhibitory effect of prostacyclin (PGI2) on the platelet stimulation of thrombin generation. The loss of the inhibitory effect was due to the loss of high-affinity prostanoid receptors, which may contribute to atherogenesis in SCI. Incubation of normal, non-SCI platelets in SCI plasma (n = 12) also resulted in the loss of high-affinity binding of PGI2 (Kd1 = 9.1 �� 2.0 nM; n1 = 170 �� 32 sites per cell vs. Kd1 = 7.2 �� 1.1 nM; n1 = 23 �� 8 sites per cell), with no significant change in the low-affinity receptors (Kd2 = 1.9 �� 0.1 ��M; n2 = 1,832 �� 232 sites per cell vs. Kd2 = 1.6 �� 0.1 ��M; n2 = 1,740 �� 161 sites per cell) as determined by Scatchard analysis of the binding of [3H]PGE1. The loss of high-affinity PGI2 binding led to the failure of PGI2 to inhibit the platelet-stimulated thrombin generation. The increase of cellular cyclic AMP level, mediated through the binding of PGI2 to low-affinity receptors in platelets, was unaffected in SCI platelets. PAGE and immunoblot of SCI plasma showed the presence of an IgG band, which specifically blocked the binding of [3H]PGE1 to the high-affinity PGI2 receptors of normal platelets. PAGE of the reduced IgG band, the amino acid sequence of the novel band as a heavy chain of IgG that inhibits the binding of [3H]PGE1 to the high-affinity platelet PGI2 receptor, demonstrates that the specific recognition and inhibition of high-affinity PGI2 binding to platelets was due to an anti-prostacyclin receptor antibody present in SCI plasma.

Interaction of CTLA-4 with AP50, a clathrin-coated pit adaptor���protein

CTLA-4 plays a critical role in regulating the immune response. It is mainly located in cytoplasmic vesicles and is expressed only transiently on the surface after T cell activation. In this study, we demonstrate that CTLA-4 is associated with AP50, the medium chain of the clathrin-associated coated pit adaptor protein complex AP2. In a yeast two-hybrid screen, three individual cDNA clones that encode mouse AP50 were isolated, all of which can interact specifically with the cytoplasmic domain of mouse CTLA-4, but not with the cytoplasmic domain of mouse CD28. We have shown that CTLA-4 can bind specifically to AP50 when CTLA-4 and AP50 are cotransfected into human 293T cells. A Y201 to F201 mutation in the YVKM intracellular localization motif of the CTLA-4 cytoplasmic domain significantly diminished its binding to AP50. We also found that AP50 bound to a CTLA-4 peptide containing unphosphorylated Y201 but not to a peptide containing phosphorylated Y201. Conversely, the p85 subunit of phosphatidylinositol 3-kinase and, to a lesser extent, protein tyrosine phosphatase SYP (SHP-2) and SHP (SHP-1) bind only to the CTLA-4 peptide containing phosphorylated Y201. Therefore, the phosphorylation status of Y201 in the CTLA-4 cytoplasmic domain determines the binding specificity of CTLA-4. These results suggest that AP50 and the coated pit adaptor complex AP2 may play an important role in regulating the intracellular trafficking and function of CTLA-4.

Molecular switch in signal transduction: Reaction paths of the conformational changes in ras���p21

Conformational changes in ras p21 triggered by the hydrolysis of GTP play an essential role in the signal transduction pathway. The path for the conformational change is determined by molecular dynamics simulation with a holonomic constraint directing the system from the known GTP-bound structure (with the ��-phosphate removed) to the GDP-bound structure. The simulation is done with a shell of water molecules surrounding the protein. In the switch I region, the side chain of Tyr-32, which undergoes a large displacement, moves through the space between loop 2 and the rest of the protein, rather than on the outside of the protein. As a result, the charged residues Glu-31 and Asp-33, which interact with Raf in the homologous RafRBD���Raps complex, remain exposed during the transition. In the switch II region, the conformational changes of ��2 and loop 4 are strongly coupled. A transient hydrogen bonding complex between Arg-68 and Tyr-71 in the switch II region and Glu-37 in switch I region stabilizes the intermediate conformation of ��2 and facilitates the unwinding of a helical turn of ��2 (residues 66���69), which in turn permits the larger scale motion of loop 4. Hydrogen bond exchange between the protein and solvent molecules is found to be important in the transition. Possible functional implications of the results are discussed.

Nucleosomes, linker DNA, and linker histone form a unique structural motif that directs the higher-order folding and compaction of chromatin

The compaction level of arrays of nucleosomes may be understood in terms of the balance between the self-repulsion of DNA (principally linker DNA) and countering factors including the ionic strength and composition of the medium, the highly basic N termini of the core histones, and linker histones. However, the structural principles that come into play during the transition from a loose chain of nucleosomes to a compact 30-nm chromatin fiber have been difficult to establish, and the arrangement of nucleosomes and linker DNA in condensed chromatin fibers has never been fully resolved. Based on images of the solution conformation of native chromatin and fully defined chromatin arrays obtained by electron cryomicroscopy, we report a linker histone-dependent architectural motif beyond the level of the nucleosome core particle that takes the form of a stem-like organization of the entering and exiting linker DNA segments. DNA completes ���1.7 turns on the histone octamer in the presence and absence of linker histone. When linker histone is present, the two linker DNA segments become juxtaposed ���8 nm from the nucleosome center and remain apposed for 3���5 nm before diverging. We propose that this stem motif directs the arrangement of nucleosomes and linker DNA within the chromatin fiber, establishing a unique three-dimensional zigzag folding pattern that is conserved during compaction. Such an arrangement with peripherally arranged nucleosomes and internal linker DNA segments is fully consistent with observations in intact nuclei and also allows dramatic changes in compaction level to occur without a concomitant change in topology.

Third-generation synchrotron x-ray diffraction of 6-��m crystal of raite, ���Na3Mn3Ti0.25Si8O20(OH)2���10H2O, opens up new chemistry and physics of low-temperature���minerals

The crystal structure of raite was solved and refined from data collected at Beamline Insertion Device 13 at the European Synchrotron Radiation Facility, using a 3 �� 3 �� 65 ��m single crystal. The refined lattice constants of the monoclinic unit cell are a = 15.1(1) ���; b = 17.6(1) ���; c = 5.290(4) ���; �� = 100.5(2)��; space group C2/m. The structure, including all reflections, refined to a final R = 0.07. Raite occurs in hyperalkaline rocks from the Kola peninsula, Russia. The structure consists of alternating layers of a hexagonal chicken-wire pattern of 6-membered SiO4 rings. Tetrahedral apices of a chain of Si six-rings, parallel to the c-axis, alternate in pointing up and down. Two six-ring Si layers are connected by edge-sharing octahedral bands of Na+ and Mn3+ also parallel to c. The band consists of the alternation of finite Mn���Mn and Na���Mn���Na chains. As a consequence of the misfit between octahedral and tetrahedral elements, regions of the Si���O layers are arched and form one-dimensional channels bounded by 12 Si tetrahedra and 2 Na octahedra. The channels along the short c-axis in raite are filled by isolated Na(OH,H2O)6 octahedra. The distorted octahedrally coordinated Ti4+ also resides in the channel and provides the weak linkage of these isolated Na octahedra and the mixed octahedral tetrahedral framework. Raite is structurally related to intersilite, palygorskite, sepiolite, and amphibole.