Bacillus thuringiensis produces insecticidal proteins (Cry protoxins) during the sporulation phase as parasporal crystals. During intoxication, the Cry protoxins must change from insoluble crystals into membraneinserted toxins which form ionic pores. The structural changes of Cry toxins during oligomerization and insertion into the membrane are still unknown. The Cry1Ab toxin has nine tryptophan residues; seven are located in domain I, the pore-forming domain, and two are located in domain II, which is involved in receptor recognition. Eight Trp residues are highly conserved within the whole family of three-domain Cry proteins, suggesting an essential role for these residues in the structural folding and function of the toxin. In this work, we analyzed the role of Trp residues in the structure and function of Cry1Ab toxin. We replaced the Trp residues with phenylalanine or cysteine using site-directed mutagenesis. Our results show that W65 and W316 are important for insecticidal activity of the toxin since their replacement by Phe reduced the toxicity against Manduca sexta. The presence of hydrophobic residue is important at positions 117, 219, 226, and 455 since replacement by Cys affected either the crystal formation or the insecticidal activity of the toxin in contrast to replacement by Phe in these positions. Additionally, some mutants in positions 219, 316, and 455 were also affected in binding to brush border membrane vesicles (BBMV). This is the first report that studies the role of Trp residues in the activity of Cry toxins.
BackgroundBilingualism may protect against cognitive aging and delay the onset of dementia. However, studies comparing monolinguals and bilinguals on such metrics have produced inconsistent results complicated by confounding variables and methodological concerns.MethodsWe addressed this issue by comparing cognitive performance in a more culturally homogeneous cohort of older Spanish-speaking monolingual (n = 289) and Spanish-English bilingual (n = 339) Mexican-American immigrants from the Sacramento Longitudinal Study on Aging.ResultsAfter adjusting for demographic differences and depressive symptoms, both groups performed similarly at baseline on verbal memory but the bilingual group performed significantly better than the monolingual group on a cognitive screening test, the Modified Mini-Mental State Examination (3MS; p < 0.001). Group differences on the 3MS were driven by language/executive and language/praxis factors. Within the bilingual group, neither language of testing nor degree of bilingualism was significantly associated with 3MS or verbal memory scores. Amongst individuals who performed in the normal or better range on both tests at baseline and were followed for an average of 6 years, both monolinguals and bilinguals exhibited similar rates of cognitive decline on both measures.ConclusionsThese findings suggest that bilingualism is associated with modest benefits in cognitive screening performance in older individuals in cross-sectional analyses that persist across longitudinal analyses. The effects of bilingualism should be considered when cognitively screening is performed in aging immigrant populations.Electronic supplementary materialThe online version of this article (doi:10.1186/s12877-016-0368-1) contains supplementary material, which is available to authorized users.
Estudios recientes llevados a cabo en la costa occidental de México han dado a conocer un gran número de arrecifes o parches coralinos en la región, pero aún hay áreas poco conocidas. Una de ellas es el Archipiélago de las Islas Marías (21ºN), formado por cuatro islas: María Madre, María Magdalena, María Cleofas y San Juanito. El objetivo de este trabajo fue llevar a cabo una evaluación general de la situación de los corales del archipiélago por medio de la revisión del elenco sistemático de las especies, y del análisis de la estructura comunitaria y los patrones biogeográficos de la fauna. En agosto de 1997 se visitaron 21 sitios en la Isla María Madre y 2 en San Juanito, y en cada uno se realizó un transecto de video (150 m de largo) para denotar la zonación coralina y uno de línea (20 m de largo) para hacer análisis cuantitativos. Esa información fue complementada con revisiones de literatura y datos de ejemplares de museos de México y Estados Unidos. Una vez obtenido el elenco sistemático de corales de las islas, se calculó el nivel de similitud de la fauna con el de cinco regiones cercanas (incluyendo las Islas Revillagigedo y el margen continental entre 23ºN y 18ºN), y se condujeron análisis de ordenación. En el campo se observaron 13 especies de corales pétreos (incluyendo ocho nuevos registros), pero no se encontró a Porites baueri, especie nominalmente endémica de las Islas Marías. Las revisiones de museos arrojaron dos nuevos registros. Así, sumando la información se conocen 20 especies como residentes de la zona de estudio. En el archipiélago no se vieron arrecifes en sentido construccional pero había gran abundancia de coral, especialmente en la Isla María Madre. Las comunidades mostraban una clara zonación con Pocillopora en agua somera y Porites, Pavona y Psammocora en sitios profundos. Finalmente, el análisis biogeográfico indicó que la boca del Golfo de California representa una región clave para la inmigración de especies desde el Pacífico occidental, y las Islas Marías parecen jugar un punto nodal para la dispersión coralina hacia el norte.
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