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Structural Explanation (structural + explanation)
Selected AbstractsCrystal structures of bovine ,-lactoglobulin in the orthorhombic space group C2221FEBS JOURNAL, Issue 2 2001Structural differences between genetic variants A, features of the Tanford transition The crystal structures of ,-lactoglobulin genetic variants A and B have been determined in the orthorhombic space group C2221 (lattice Y) by X-ray diffraction at 2.0 Ĺ and 1.95 Ĺ resolution, respectively. The structural comparison shows that both variants exhibit the open conformation of the EF loop at the pH of crystallization (pH 7.9), in contrast to what has been reported for the same genetic variants at pH 7.1 in the trigonal space group P3221 (lattice Z) [Qin, B.Y., Bewley, M.C., Creamer, L.K., Baker, E.N. & Jameson, G.B. (1999) Protein Sci.8, 75,83]. Furthermore, it was found that the stereochemical environment of Tyr42 changes significantly with pH variation between pH 7 and pH 8. This may provide a structural explanation for an as yet unexplained feature of the Tanford transition, namely the increase in exposure of a tyrosine residue. [source] Gender Asymmetry in Family Migration: Occupational Inequality or Interspousal Comparative Advantage?JOURNAL OF MARRIAGE AND FAMILY, Issue 2 2010Kimberlee A. Shauman This paper examines gender inequality in the determinants of job-related long-distance migration among married dual-earner couples during the 1980s and 1990s. The analysis tested the structural explanation, which attributes gender asymmetry in family migration to structural inequality in the labor market, and the comparative advantage explanation derived from relative resource theory. The analysis used individual- and family-level data from 5,504 Panel Study of Income Dynamics families, occupation-level data from the 1980,2000 U.S. Decennial Censuses Integrated Public Use Micro Samples, and discrete-time event history models. Gender differences in the determinants of family migration were not explained by gender differences in occupational characteristics, but the results partially support the relative resource theory by illustrating the conditioning influence of interspousal comparative advantage. [source] Limited tendency of ,-helical residues to form disulfide bridges: a structural explanationJOURNAL OF PEPTIDE SCIENCE, Issue 12 2006Alfonso De Simone Abstract Disulfide bridges have an enormous impact on the structure of a large number of proteins and polypeptides. Understanding the structural basis that regulates their formation may be important for the design of novel peptide-based molecules with a specific fold and stability. Here we report a statistical analysis of the relationships between secondary structure and disulfide bond formation, carried out using a large database of protein structures. Our analyses confirm the observation sporadically reported in previous investigations that cysteine residues located in ,-helices display a limited tendency to form disulfide bridges. The very low occurrence of the disulfide bond in all ,-chains compared to all ,-chains indicates that this property is also evident when proteins with different topologies are investigated. Taking advantage of the large database that endorsed the analysis on relatively rare motifs, we demonstrate that cysteine residues embedded in 310 helices present a good tendency to form disulfide bonds. This result is somewhat surprising since 310 helices are commonly assimilated into ,-helices. A plausible structural explanation for the observed data has been derived combining analyses of disulfide bond sequence separation and of the length of the different secondary structure elements. Copyright © 2006 European Peptide Society and John Wiley & Sons, Ltd. [source] The origins, early development and status of Bourdieu's concept of ,cultural capital'THE BRITISH JOURNAL OF SOCIOLOGY, Issue 1 2005Derek Robbins Abstract The paper examines the context of the first introduction of the concept of ,cultural capital' in the sociology of education analyses undertaken in the early 1960s and published by Bourdieu in collaboration with Jean-Claude Passeron in ,Les étudiants et leurs études' (1964a) and Les Héritiers (1964b). It first considers the cultural contexts within which Bourdieu's thinking about culture originated , both in relation to his social origins and in relation to his intellectual training. It then examines the extent to which Bourdieu's early anthropological research in Algeria was influenced by his knowledge of American acculturation theory. It concludes that Bourdieu sought to use acculturation theory in a distinctive way , one which he articulated more confidently as he explored the relationship between agency and structural explanation in the late 1960s and early 1970s. The specific educational researches which stimulated the articulation of the concept of ,linguistic' or ,cultural' capital belonged to the period in which Bourdieu was only just beginning to refine his post-structuralist philosophy of social scientific explanation. To use these concepts now involves deploying them reflexively in accordance with Bourdieu's later thinking rather than at face value as they were first developed during the period in which he and Passeron were ,apprentice' researchers. [source] Adenosine binding to low-molecular-weight purine nucleoside phosphorylase: the structural basis for recognition based on its complex with the enzyme from Schistosoma mansoniACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2010Humberto M. Pereira Schistosomes are unable to synthesize purines de novo and depend exclusively on the salvage pathway for their purine requirements. It has been suggested that blockage of this pathway could lead to parasite death. The enzyme purine nucleoside phosphorylase (PNP) is one of its key components and molecules designed to inhibit the low-molecular-weight (LMW) PNPs, which include both the human and schistosome enzymes, are typically analogues of the natural substrates inosine and guanosine. Here, it is shown that adenosine both binds to Schistosoma mansoni PNP and behaves as a weak micromolar inhibitor of inosine phosphorolysis. Furthermore, the first crystal structures of complexes of an LMW PNP with adenosine and adenine are reported, together with those with inosine and hypoxanthine. These are used to propose a structural explanation for the selective binding of adenosine to some LMW PNPs but not to others. The results indicate that transition-state analogues based on adenosine or other 6-amino nucleosides should not be discounted as potential starting points for alternative inhibitors. [source] Structure and sugar-specificity of basic winged-bean lectin: structures of new disaccharide complexes and a comparative study with other known disaccharide complexes of the lectinACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2008Kiran A. Kulkarni Crystal structures of the complexes of basic winged-bean agglutinin with the disaccharides Gal,1-4Gal (galabiose), Gal,1-6Glc (mellibiose) and Gal,1-4Gal,-Et have been determined and the complex with Gal,1-2Gal has been modelled. The interactions of the nonreducing Gal with the lectin at the primary site are the same as those in the known complexes with disaccharides having the ,1,3 linkage. The second residue in Gal,1-4Gal and Gal,1-6Glc forms a water bridge to the lectin, while the ethyl group in Gal,1-4Gal,-Et makes nonpolar interactions. In complexes involving disaccharides with ,1-3 linkages, which form part of the A and B blood-group substances, the second sugar residue forms a direct hydrogen bond to the variable loop in the binding site of the lectin. This in part explains the specificity of the lectin for the blood-group substances and also the higher affinity of ,1,3-linked disaccharides for the lectin compared with disaccharides involving other linkages. Including those reported here, 14 crystal structures involving the lectin, accounting for 54 crystallographically independent subunits, are available. A comparative study of these structures shows that the region involving the curved ,-sheet which nestles the metal ions is relatively rigid. The carbohydrate-binding region is perched on this region. The flat ,-sheet, which is involved in oligomerization and exhibits considerable variability in legume lectins, is relatively flexible. Indeed, the structures of basic winged-bean lectin have been of critical importance in establishing legume lectins as a family of proteins in which small alterations in essentially the same tertiary structure lead to large variations in quaternary association. They have also provided a structural explanation of the blood-group specificity of the lectin. [source] GABAB receptor function in the ileum and urinary bladder of wildtype and GABAB1 subunit null miceAUTONOMIC & AUTACOID PHARMACOLOGY, Issue 3 2002G. J. Sanger Summary1 GABAB1 receptor subunit knockout mice were generated and the effects of the GABAB receptor agonist, baclofen, were evaluated within the peripheral nervous system (PNS) of wildtype (+/+), heterozygote (+/,) and knockout (,/,) animals. For this purpose, neuronally-mediated responses were evoked in both the isolated ileum and urinary bladder, using selective electrical field stimulation (EFS). 2 In ileum resected from 4,8-week-old-mice, low frequencies of EFS (0.5 Hz) evoked irregular muscle contractions which were prevented by atropine 1 ,M and reduced by baclofen (33.4 ± 5.6%, 100 ,m). The latter effect was antagonized by the GABAB receptor antagonist CGP54626 0.2 ,m. Baclofen 100 ,m did not affect contractions of similar amplitude induced by carbachol, indicating that the ability of baclofen to inhibit cholinergic function in mouse ileum may be due to an action at prejunctional GABAB receptors. 3 To avoid the development of grand mal seizure by GABAB1 (,/,) mice, a behaviour observed when the mice were greater than 3 weeks old, it was necessary to study the effects of this knockout in 1,3-week-old-animals. However, at this age, EFS at 0.5 Hz did not evoke robust muscle contractions. Consequently we used EFS at 5 Hz, which did evoke cholinergically mediated contractions, found to be of similar amplitude in (+/+) and (+/,) mice, of both 1,3 weeks and 4,8 weeks of age. At this frequency of EFS, baclofen reduced the amplitude of the evoked contractions [n=6 (+/+) and n=5 (+/,), IC50 19.2 ± 4.8 ,m) and this effect was greatly reduced in the presence of CGP54626 0.2 ,m. 4 In urinary bladder from 1,3-week-old-mice, using higher frequencies of EFS to evoke clear, nerve-mediated contractions (10 Hz), baclofen 10,300 ,m concentration-dependently inhibited contractions in (+/+) mice (IC50 9.6 ± 3.8 ,m). This effect was inhibited by CGP54626 (0.2 ,m, 46.2 ± 13.6% inhibition, 300 ,m baclofen n=7) a concentration which, by itself, had no effect on the EFS-evoked contractions. 5 The effects of baclofen in both ileum and urinary bladder were absent in the GABAB1 receptor subunit (,/,) mice; however, responses to EFS were unaffected in (,/,) when compared to the (+/+) mice. 6 Our data suggest that, as in the central nervous system (CNS), the GABAB1 receptor subunit is an essential requirement for GABAB receptor function in the enteric and PNS. As such, these data do not provide a structural explanation for the existence of putative subtypes of GABAB receptor, suggested by studies such as those in which different rank-orders of GABAB agonist affinity have been reported in different tissues. [source] Black Employment, Segregation, and the Social Organization of Metropolitan Labor MarketsECONOMIC GEOGRAPHY, Issue 3 2007Niki T. Dickerson Abstract: This broad analysis of the employment of blacks in metropolitan areas examines the role of residential segregation in comparison with four other key structural explanations for racial metropolitan inequality: industrial composition, minority concentration, immigration, and the racial disparity in skills. The goal of the analysis was to determine whether the spatial configuration of blacks relative to whites in a metropolitan area influences the employment rates of black men and black women in the context of the structural conditions of the local labor market. The study expanded the analysis of space and work beyond an emphasis on the physical distance between black communities and jobs to a broader conceptualization of residential segregation as a structural feature of the entire metropolitan labor market that is representative of its social organization with regard to race. Using a longitudinal data set of the structural characteristics of the 95 largest U.S. cities from the 1980, 1990, and 2000 decennial censuses, the study used a cross-sectional analysis of the cities in 2000 and a fixed-effects analysis to assess the impact of five dimensions of residential segregation and the four other structural factors on the employment of blacks across different labor markets and across time within each labor market. The results revealed that when the other structural characteristics are controlled, the employment rates of blacks are lower in more segregated cities and decrease as cities become more segregated over time. The clustering and evenness dimensions of residential segregation were the most determinative of black employment. [source] | |||||||||||||