Seafloor spreading of the third arm of the Afar triple junction: A review.

The only place within the East African Rift System where seafloor spreading is being manifested along with new crust being formed is at the Afar triple junction, a seismically active area defined by latitude 9°N to 14°N and longitude 43E° to 49E°. Previous seafloor spreading studies have primarily concentrated on the Aden-Owen Carlsberg Ridge (AOCR). The AOCR defines the boundary between the Eastern Gulf of Aden and the Western Gulf of Aden. Although the previous studies have provided insight into seafloor spreading rates, the timing of seafloor spreading, particularly in the Western Gulf of Aden (encompassing the study area) remains unclear. This study seeks to estimate the rates of seafloor spreading by reviewing data from previous studies and integrating geophysical (paleomagnetic anomalies), geological data and systematically estimating seafloor spreading rates and determining the timing of the initial seafloor spreading in the Afar region using advanced geo-software (Gplates). The results from our modeling show that the initial seafloor spreading began approximately 16 million years ago, with spreading rates varying from 12.29 to 20.12 mm/yr (average = 15.75 mm/yr). The average seafloor spreading rates in the study area are nearly 1.5-fold lower than the average seafloor spreading in the Eastern Gulf of Aden (23 mm/yr). The predominant seafloor spreading in the study area is East-West. Further, the angular rotation of the Somalian plate against the Arabian plate has been estimated to be 0.5353°/Ma. The study enhances understanding of plate tectonics, seismic hazards, volcanism and hydrocarbon systems in the Afar region.

Taking a look at the calibration of a CCD detector with a fiber-optic taper.

At the Structural Biology Center beamline 19BM, located at the Advanced Photon Source, the operational characteristics of the equipment are routinely checked to ensure they are in proper working order. After performing a partial flat-field calibration for the ADSC Quantum 210r CCD detector, it was confirmed that the detector operates within specifications. However, as a secondary check it was decided to scan a single reflection across one-half of a detector module to validate the accuracy of the calibration. The intensities from this single reflection varied by more than 30% from the module center to the corner of the module. Redistribution of light within bent fibers of the fiber-optic taper was identified to be a source of this variation. The degree to which the diffraction intensities are corrected to account for characteristics of the fiber-optic tapers depends primarily upon the experimental strategy of data collection, approximations made by the data processing software during scaling, and crystal symmetry.

Structure of a novel dodecaheme cytochrome c from Geobacter sulfurreducens reveals an extended 12 nm protein with interacting hemes.

Multiheme cytochromes c are important in electron transfer pathways in reduction of both soluble and insoluble Fe(III) by Geobacter sulfurreducens. We determined the crystal structure at 3.2Å resolution of the first dodecaheme cytochrome c (GSU1996) along with its N-terminal and C-terminal hexaheme fragments at 2.6 and 2.15Å resolution, respectively. The macroscopic reduction potentials of the full-length protein and its fragments were measured. The sequence of GSU1996 can be divided into four c(7)-type domains (A, B, C and D) with homology to triheme cytochromes c(7). In cytochromes c(7) all three hemes are bis-His coordinated, whereas in c(7)-type domains the last heme is His-Met coordinated. The full-length GSU1996 has a 12nm long crescent shaped structure with the 12 hemes arranged along a polypeptide to form a "nanowire" of hemes; it has a modular structure. Surprisingly, while the C-terminal half of the protein consists of two separate c(7)-type domains (C and D) connected by a small linker, the N-terminal half of the protein has two c(7)-type domains (A and B) that form one structural unit. This is also observed in the AB fragment. There is an unexpected interaction between the hemes at the interface of domains A and B, which form a heme-pair with nearly parallel stacking of their porphyrin rings. The hemes adjacent to each other throughout the protein are within van der Waals distance which enables efficient electron exchange between them. For the first time, the structural details of c(7)-type domains from one multiheme protein were compared.

Analysis of resistance testing in South Trinidad / Análisis de prueba de resistencia en Trinidad Sur

The introduction of antiretroviral therapy in Trinidad and Tobago in the 1980s has resulted in a decrease in mortality of HIV-infected persons. Poor adherence to antiretroviral therapy (ART) has resulted in the development of multidrug resistant HIV. Resistance testing done on 40 samples showed that 64.8% of patients had K103 mutation, 75.6% of patients had M184 mutations and 62% of patients showed resistance to tenofovir suggesting that the K65R mutation was highly likely to be present. There was reduced activity to the protease inhibitors; no resistance was found to the protease inhibitor, darunavir. Thus, there is a need for salvage therapy to be introduced which will result in virologic suppression and potentially stop the spread of multidrug resistant HIV. Darunavir, a new generation protease inhibitor, is an essential part of salvage therapy and needs to be introduced into the national formulary.

La introducción de la terapia antiretroviral en Trinidad y Tobago en la década de 1980, ha producido una disminución en la mortalidad de personas infectadas por el VIH. La adhesión pobre a la terapia antiretroviral (TAR) ha conducido al desarrollo de una variedad de VIH resistente a las multidrogas. Las pruebas de resistencia realizadas a 40 muestras mostró que el 64.8% de los pacientes tenían mutación K103, 75.6% de los pacientes tenían mutaciones M184, y 62% de pacientes mostraron resistencia al tenofovir, lo que indica una alta probabilidad de mutación K65R. Había actividad reducida respecto a los inhibidores de la proteasa; mientras que no se halló ninguna resistencia en el inhibidor de la protease, darunavir. Así, hay necesidad de introducir una terapia de salvamento qué produzca una supresión virológica y potencialmente detenga la diseminación del VIH resistente a las multidrogas. El darunavir - inhibidor de nueva generación frente a la proteasa -es una parte fundamental de la terapia de salvamento y necesita ser introducido en el formulario nacional.

Analysis of resistance testing in South Trinidad.

The introduction of antiretroviral therapy in Trinidad and Tobago in the 1980s has resulted in a decrease in mortality of HIV-infected persons. Poor adherence to antiretroviral therapy (ART) has resulted in the development of multidrug resistant HIV Resistance testing done on 40 samples showed that 64.8% of patients had K103 mutation, 75.6% of patients had M184 mutations and 62% of patients showed resistance to tenofovir suggesting that the K65R mutation was highly likely to be present. There was reduced activity to the protease inhibitors; no resistance was found to the protease inhibitor, darunavir. Thus, there is a need for salvage therapy to be introduced which will result in virologic suppression and potentially stop the spread of multidrug resistant HIV Darunavir a new generation protease inhibitor, is an essential part of salvage therapy and needs to be introduced into the national formulary.

Structural characterization of a family of cytochromes c(7) involved in Fe(III) respiration by Geobacter sulfurreducens.

Periplasmic cytochromes c(7) are important in electron transfer pathway(s) in Fe(III) respiration by Geobacter sulfurreducens. The genome of G. sulfurreducens encodes a family of five 10-kDa, three-heme cytochromes c(7). The sequence identity between the five proteins (designated PpcA, PpcB, PpcC, PpcD, and PpcE) varies between 45% and 77%. Here, we report the high-resolution structures of PpcC, PpcD, and PpcE determined by X-ray diffraction. This new information made it possible to compare the sequences and structures of the entire family. The triheme cores are largely conserved but are not identical. We observed changes, due to different crystal packing, in the relative positions of the hemes between two molecules in the crystal. The overall protein fold of the cytochromes is similar. The structure of PpcD differs most from that of the other homologs, which is not obvious from the sequence comparisons of the family. Interestingly, PpcD is the only cytochrome c(7) within the family that has higher abundance when G. sulfurreducens is grown on insoluble Fe(III) oxide compared to ferric citrate. The structures have the highest degree of conservation around "heme IV"; the protein surface around this heme is positively charged in all of the proteins, and therefore all cytochromes c(7) could interact with similar molecules involving this region. The structures and surface characteristics of the proteins near the other two hemes, "heme I" and "heme III", differ within the family. The above observations suggest that each of the five cytochromes c(7) could interact with its own redox partner via an interface involving the regions of heme I and/or heme III; this provides a possible rationalization for the existence of five similar proteins in G. sulfurreducens.

Crystallization and preliminary X-ray diffraction analysis of the glucuronoyl esterase catalytic domain from Hypocrea jecorina.

The catalytic domain of the glucuronoyl esterase from Hypocrea jecorina (anamorph Trichoderma reesei) was overexpresssed, purified and crystallized by the sitting-drop vapor-diffusion method using 1.4 M sodium/potassium phosphate pH 6.9. The crystals belonged to space group P2(1)2(1)2(1) and X-ray diffraction data were collected to 1.9 A resolution. This is the first enzyme with glucoronoyl esterase activity to be crystallized; its structure will be valuable in lignocellulose-degradation research.

Structures and solution properties of two novel periplasmic sensor domains with c-type heme from chemotaxis proteins of Geobacter sulfurreducens: implications for signal transduction.

Periplasmic sensor domains from two methyl-accepting chemotaxis proteins from Geobacter sulfurreducens (encoded by genes GSU0935 and GSU0582) were expressed in Escherichia coli. The sensor domains were isolated, purified, characterized in solution, and their crystal structures were determined. In the crystal, both sensor domains form swapped dimers and show a PAS-type fold. The swapped segment consists of two helices of about 45 residues at the N terminus with the hemes located between the two monomers. In the case of the GSU0582 sensor, the dimer contains a crystallographic 2-fold symmetry and the heme is coordinated by an axial His and a water molecule. In the case of the GSU0935 sensor, the crystals contain a non-crystallographic dimer, and surprisingly, the coordination of the heme in each monomer is different; monomer A heme has His-Met ligation and monomer B heme has His-water ligation as found in the GSU0582 sensor. The structures of these sensor domains are the first structures of PAS domains containing covalently bound heme. Optical absorption, electron paramagnetic resonance and NMR spectroscopy have revealed that the heme groups of both sensor domains are high-spin and low-spin in the oxidized and reduced forms, respectively, and that the spin-state interconversion involves a heme axial ligand replacement. Both sensor domains bind NO in their ferric and ferrous forms but bind CO only in the reduced form. The binding of both NO and CO occurs via an axial ligand exchange process, and is fully reversible. The reduction potentials of the sensor domains differ by 95 mV (-156 mV and -251 mV for sensors GSU0582 and GSU0935, respectively). The swapped dimerization of these sensor domains and redox-linked ligand switch might be related to the mechanism of signal transduction by these chemotaxis proteins.

Development of a real-time timing-shutter performance monitor for protein crystallography.

In order to accurately monitor shutter timing events and long-term shutter performance, a timing-shutter monitor has been developed. This monitor uses a photodiode to capture X-ray-induced fluorescence from the shutter blade in synchrony with goniometer rotation to measure shutter opening and closing delay times, as well as the total time that X-rays are exposed to the sample during crystallographic data frames.

Identifying psychosocial problems among youth: factors associated with youth agreement on a positive parent-completed PSC-17.

BACKGROUND: The choice of informant is a critical piece in the identification of psychosocial problems in youth. While many behavioural measures have been adapted to include information from multiple sources, in the case of parents and youth, poor agreement has been found. Our study purpose was to identify youth and parent factors associated with whether the youth agrees with a positive parent-completed screen of youth psychosocial problems. METHODS: Parents of youth aged 10-15 years who were seen for a medical visit at eight clinics completed the 17-item Pediatric Symptom Checklist (PSC-17). Youth scoring positive on the screen and their parents/guardians were interviewed by telephone after the visit (n = 145). We conducted bivariate and multivariate analyses to identify parent characteristics and child factors associated with whether the youth agrees with the positive parent-completed screen. RESULTS: Fifty per cent of youth participants agreed with their parent on a positive parent-completed PSC-17 based on their completion of the Y-PSC-17 as a self-report measure. Youth who reported a positive Y-PSC-17 in agreement with their parent were twice as likely to meet diagnostic cut-offs on sub-scales of anxiety/depression and aggression on the Child Behaviour Checklist (P < 0.01 and P < 0.05 respectively), reported lower parent-child connectedness (P < 0.01) and their parents reported more anger/frustration (P < 0.05) than youth who disagreed with the positive parent-completed screen. Most of these associations remained significant when controlling for the other factors and demographic characteristics in multivariate analysis. CONCLUSIONS: Findings indicate that when the youth agrees with a positive parent-completed PSC-17, there is higher parent frustration, lower parent-child connectedness, and the youth is more likely to have a diagnosis of an emotional or behavioural disorder. Thus, when possible, the use of both parent and youth as informants provides necessary information in formulating a comprehensive treatment strategy to address the psychosocial needs of youth.

Two-year-olds will name artifacts by their functions.

Do young children take functional information into account in naming artifacts? In three studies of lexical categorization, 112 children 2 years of age learned new names for novel artifacts with novel functions and then extended the names to new objects. The objects were designed to have functions that were causally related in simple and compelling ways to perceptible aspects of their physical structure. Despite only minimal opportunity to familiarize themselves with the objects, children generalized the names in accordance with the objects' functions. This result obtained even when children had to discover the functions of the named objects on their own (Experiment 2) and when all the test objects had some discernible function (Experiment 3). Two-year-olds name by function when they can make sense of the relation between the appearances and the functions of artifacts.

Purification, crystallization and preliminary X-ray analysis of murine interleukin-5.

Wild-type and mutant forms of murine interleukin-5 (mIL-5) have been expressed in the baculovirus expression system, purified, and used in crystallization trials. Attempts to obtain diffraction quality crystals of wild-type protein were unsuccessful. The substitution of glutamine for Asn75 preserved biological activity, while removing one of two predicted N-linked glycosylation sites, and the resulting protein was crystallized from polyethylene glycol 8000 at pH 7.8 in two crystal forms. The orthorhombic crystals, which belong to space group P2(1)2(1)2 with cell dimensions a = 55.9 A, b = 83.0 A and c = 52.3 A, diffract to beyond 2.5 A resolution. The second crystal form belongs to a trigonal space group, either P3(1)21 or P3(2)21, with cell dimensions a = b = 62.1 A, c = 129.9 A, and diffracts to about 3.8 A resolution. Each crystal form probably contains one mIL-5 dimer per asymmetric unit.

Structural and molecular modeling studies of quinazolinone anticonvulsants.

Studies of derivatives of the anticonvulsant methaqualone led to the discovery that unsaturation in the 2-substituent produced active but less toxic compounds; accordingly, 2-arylethanone derivatives have been developed. The crystal structures of five 2-arylethanone derivatives of methaqualone were determined to probe structure-activity relationships. Although these compounds display different activities, the solid-state and calculated structures are similar: each compound is observed as the neamine tautomer containing an intramolecular hydrogen bond between the ethanone and the amine N atom and the molecular conformations are the same. These studies conclude that recognition of the anticonvulsants arises from specific binding of an ortho substituent on the N(3) phenyl substituent, rather than from binding of a particular conformation or tautomeric form adopted by the compound containing an ortho substituent, and that such recognition is characteristic of a broad range of anticonvulsant drugs. Crystal data: [see text].

Molecular modeling and crystallographic studies of 4-amino-N-phenylbenzamide anticonvulsants.

The molecular structures of five different MES-active N-phenylbenzamides were determined by X-ray diffraction methods, and the conformations of a series of active and inactive benzamides were analyzed by molecular mechanics calculations. The most active compounds adopt a similar, consistent conformation in both the experimentally determined crystallographic structures and in the calculated molecular mechanics structures. This conformation places one o-methyl group proximal to the NH group of the central amide plane and orients the methyl-substituted phenyl ring at an angle of 90 degrees to 120 degrees to the central amide plane. Intermolecular interactions in the crystal structures indicate that hydrogen bonding to the central amide group is the important interaction. The observed consistent conformation facilitates formation of hydrogen bonds to the carbonyl oxygen atom. The conformations of inactive compounds obstruct this interaction. These findings help to outline a model of some of the structural features which this series of benzamides must possess in order to demonstrate MES anticonvulsant activity.

Structure of suriclone, a benzodiazepine receptor agonist.

6-(7-Chloro-1,8-naphthyridin-2-yl)-2,3,6,7-tetrahydro-4-methyl-7- oxo-5H-1,4-dithiino[2,3-c]-pyrrol-5-yl-1-piperazinecarboxylic++ + acid, C20H20C1N5-O3S2, Mr = 477.9, triclinic, P1, a = 8.7066 (3), b = 9.7665 (8), c = 14.2515 (16) A, alpha = 80.986 (9), beta = 75.168 (6), gamma = 65.884 (5) degrees, V = 1067.4 (2) A3, Z = 2, F(000) = 496, room temperature, Dm = 1.482, D chi = 1.487 g cm-3, lambda(Cu K alpha) = 1.54178 A, Ni filter, mu = 36.3 cm-1, R = 0.053, omega R = 0.070 for the 3538 reflections included in the refinement. Comparisons of the structures of the two enantiomers of suriclone and the active conformer of the 1,4-benzodiazepine anxiolytics allow the identification of the active form of suriclone as the R isomer.