The class I major histocompatibility (MHC) molecule is a heterotrimer composed of a heavy chain, the small subunit beta(2)-microglobulin (beta(2)m), and a peptide. Fluorescence anisotropy has been used to assay the interaction of a labeled peptide with a recombinant, soluble form of the class I MHC HLA-A2. Consistent with earlier work, peptide binding is shown to be a two-step process limited by a conformational rearrangement in the heavy chain/beta(2)m heterodimer. However, we identify two pathways for peptide dissociation from the heterotrimer: (1) initial peptide dissociation leaving a heavy chain/beta(2)m heterodimer and (2) initial dissociation of beta(2)m, followed by peptide dissociation from the heavy chain. Eyring analyses of rate constants measured as a function of temperature permit for the first time a complete thermodynamic characterization of peptide binding. We find that in this case peptide binding is mostly entropically driven, likely reflecting the hydrophobic character of the peptide binding groove and the peptide anchor residues. Thermodynamic and kinetic analyses of peptide-MHC interactions as performed here may be of practical use in the engineering of peptides with desired binding properties and will aid in the interpretation of the effects of MHC and peptide substitutions on peptide binding and T cell reactivity. Finally, our data suggest a role for beta(2)m in dampening conformational dynamics in the heavy chain. Remaining conformational variability in the heavy chain once beta(2)m has bound may be a mechanism to promote promiscuity in peptide binding.
The cycles of carbon, nitrogen and phosphorus are essential components of the processes and functioning of ecosystems. The functional capacity of the soil microbial community that drives these cycles varies among soils dominated by different plant species. This work aims to quantify changes in soil features of coastal ecosystems of the Iberian Peninsula caused by the invasion of Carpobrotus edulis by analysing soil chemical properties and extracellular soil enzymes. We also analyse the influence of these changes on the germination and early development of native species Malcolmia littorea (L.) R.Br. and Scabiosa atropurpupea L. and the alien C. edulis. Our results reveal that when C. edulis invades a dune ecosystem, it causes significant changes to pH, enzymatic activities, nutrients, salinity and moisture content of the soil (the level of the change depends on the initial characteristics of the invaded ecosystem). These changes alter the germination process of native and invasive plants in different ways. The results of this work suggest mechanism whereby C. edulis competes with native species at an early stage and breaks the initial abiotic resistance of newly invaded landscapes. This study highlights the importance of studying the effects of invasive plant-soil interactions on the germination and emergence of different plant species in order to fully understand the effects of invasion and to consider options for restoration activities in areas invaded by C. edulis.
El principal objetivo del trabajo fue determinar si hay un aumento en la atención, la motivación y el desempeño académico de los estudiantes universitarios, cuando las sesiones de clases se llevan a cabo en un ambiente enriquecido en el uso de prácticas docentes basadas en los principios de las ciencias del cerebro. La investigación tuvo un diseño de metodología mixta. Se desarrolló un experimento con dos grupos de la misma asignatura y con el mismo profesor. En el grupo experimental se aplicaron las prácticas docentes ricas en uso de prácticas basadas en recomendaciones de la neurociencia, mientras el grupo control se impartió en un ambiente académico tradicional. Como herramientas de recolección de datos fueron utilizadas la observación no participante, dos pruebas estandarizadas y una encuesta semanal para medir los niveles de motivación. Los resultados mostraron que las tres variables dependientes analizadas (atención, motivación y desempeño académico) fueron superiores en el grupo experimental. Estos hallazgos invitan a la inclusión de los temas de neurociencia en la agenda de investigación educativa.
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