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The aggregation of Aß42 peptides is considered as one of the main causes for the development of Alzheimer's disease. In this context, Zn2+ and Cu2+ play a significant role in regulating the aggregation mechanism, due to changes in the structural and the solvation free energy of Aß42. In practice, experimental studies are not able to determine the latter properties, since the Aß42-Zn2+ and Aß42-Cu2+ peptide complexes are intrinsically disordered, exhibiting rapid conformational changes in the aqueous environment. Here, we investigate atomic structural variations and the solvation thermodynamics of Aß42, Aß42-Cu2+ , and Aß42-Zn2+ systems in explicit solvent (water) by using quantum chemical structures as templates for a metal binding site and combining extensive all-atom molecular dynamics (MD) simulations with a thorough solvation thermodynamic analysis. Our results show that the zinc and copper coordination results in a significant decrease of the solvation free energy in the C-terminal region (Met35-Val40), which in turn leads to a higher structural disorder. In contrast, the ß-sheet formation at the same C-terminal region indicates a higher solvation free energy in the case of Aß42. The solvation free energy of Aß42 increases upon Zn2+ binding, due to the higher tendency of forming the ß-sheet structure at the Leu17-Ala42 residues, in contrast to the case of binding with Cu2+ . Finally, we find the hydrophobicity of Aß42-Zn2+ in water is greater than in the case of Aß42-Cu2+ .

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Lianas are important components of tropical forests and have significant impacts on the diversity, structure and dynamics of tropical forests. The present study documented the liana flora in a Chinese tropical region. Species richness, abundance, size-class distribution and spatial patterns of lianas were investigated in three 1-ha plots in tropical seasonal rain forests in Xishuangbanna, SW China. All lianas with > or = 2 cm diameter at breast height (dbh) were measured, tagged and identified. A total of 458 liana stems belonging to 95 species (ranging from 38 to 50 species/ha), 59 genera and 32 families were recorded in the three plots. The most well-represented families were Loganiaceae, Annonceae, Papilionaceae, Apocynaceae and Rhamnaceae. Papilionaceae (14 species recorded) was the most important family in the study forests. The population density, basal area and importance value index (IVI) varied greatly across the three plots. Strychnos cathayensis, Byttneria grandifolia and Bousigonia mekongensis were the dominant species in terms of IVI across the three plots. The mean aboveground biomass of lianas (3 396 kg/ha) accounted for 1.4% of the total community above-ground biomass. The abundance, diversity and biomass of lianas in Xishuangbanna tropical seasonal rain forests are lower than those in tropical moist and wet forests, but higher than those in tropical dry forests. This study provides new data on lianas from a geographical region that has been little-studied. Our findings emphasize that other factors beyond the amount and seasonality of precipitation should be included when considering the liana abundance patterns across scales.

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RESUMEN

Lianas are important components of tropical forests and have significant impacts on the diversity, structure and dynamics of tropical forests. The present study documented the liana flora in a Chinese tropical region. Species richness, abundance, size-class distribution and spatial patterns of lianas were investigated in three 1-ha plots in tropical seasonal rain forests in Xishuangbanna, SW China. All lianas with = 2 cm diameter at breast height (dbh) were measured, tagged and identified. A total of 458 liana stems belonging to 95 species (ranging from 38 to 50 species/ha), 59 genera and 32 families were recorded in the three plots. The most well-represented families were Loganiaceae, Annonceae, Papilionaceae, Apocynaceae and Rhamnaceae. Papilionaceae (14 species recorded) was the most important family in the study forests. The population density, basal area and importance value index (IVI) varied greatly across the three plots. Strychnos cathayensis, Byttneria grandifolia and Bousigonia mekongensis were the dominant species in terms of IVI across the three plots. The mean aboveground biomass of lianas (3 396 kg/ha) accounted for 1.4% of the total community aboveground biomass. The abundance, diversity and biomass of lianas in Xishuangbanna tropical seasonal rain forests are lower than those in tropical moist and wet forests, but higher than those in tropical dry forests. This study provides new data on lianas from a geographical region that has been little-studied. Our findings emphasize that other factors beyond the amount and seasonality of precipitation should be included when considering the liana abundance patterns across scales. Rev. Biol. Trop. 57 (1-2): 211-222. Epub 2009 June 30.

Las lianas son componentes importantes de los bosques tropicales y tienen importantes impactos en la diversidad, la estructura y la dinámica de los bosques tropicales. El presente estudio documenta la flora de lianas en una región tropical estacional china. La riqueza de especies, abundancia, clases de tamaño y patrones espaciales de distribución de las lianas fueron investigados en tres parcelas de una hectárea de bosque tropical estacional lluvioso, en Xishuangbanna, SW China. Todas las lianas con = 2 cm de diámetro a la altura del pecho (DAP) fueron medidas, etiquetadas e identificadas. Un total de 458 tallos de lianas pertenecientes a 95 especies (que van de 38 a 50 especies/ha), 59 géneros y 32 familias se registraron en las tres parcelas. Las familias mejor representadas fueron Loganiaceae, Annonceae, Papilionaceae, Apocynaceae y Rhamnaceae. Papilionaceae (14 especies registradas) fue la de mayor importancia. La densidad de población, área basal y el índice de valor de importancia (IVI) varió mucho a través de las tres parcelas. Strychnos cathayensis, Byttneria grandifolia y Bousigonia mekongensis fueron las especies dominantes en términos de IVI en las tres parcelas. La media de la biomasa aérea de lianas (3 396 kg/ha) representó el 1.4% de la biomasa aérea total de la comunidad. La abundancia, biomasa y diversidad de lianas en bosques tropicales estacionales de Xishuangbanna son inferiores a los de zonas tropicales y bosques húmedos, pero superiores a los de los bosques tropicales secos. Este estudio proporciona nuevos datos sobre las lianas de una región geográfica que ha sido poco estudiada. Los resultados enfatizan que otros factores, además de la cantidad y la estacionalidad de la precipitación, deben ser considerados al examinar los patrones de la abundancia de lianas.

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