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‣ Estrogen receptor (ER) modulators each induce distinct conformational changes in ER α and ER β

Paige, Lisa A.; Christensen, Dale J.; Grøn, Hanne; Norris, John D.; Gottlin, Elizabeth B.; Padilla, Karen M.; Chang, Ching-yi; Ballas, Lawrence M.; Hamilton, Paul T.; McDonnell, Donald P.; Fowlkes, Dana M.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 30/03/1999 Português
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455.77797%
Estrogen receptor (ER) modulators produce distinct tissue-specific biological effects, but within the confines of the established models of ER action it is difficult to understand why. Previous studies have suggested that there might be a relationship between ER structure and activity. Different ER modulators may induce conformational changes in the receptor that result in a specific biological activity. To investigate the possibility of modulator-specific conformational changes, we have applied affinity selection of peptides to identify binding surfaces that are exposed on the apo-ERs α and β and on each receptor complexed with estradiol or 4-OH tamoxifen. These peptides are sensitive probes of receptor conformation. We show here that ER ligands, known to produce distinct biological effects, induce distinct conformational changes in the receptors, providing a strong correlation between ER conformation and biological activity. Furthermore, the ability of some of the peptides to discriminate between different ER α and ER β ligand complexes suggests that the biological effects of ER agonists and antagonists acting through these receptors are likely to be different.

‣ Ozone depletion and UVB radiation: Impact on plant DNA damage in southern South America

Rousseaux, M. Cecilia; Ballaré, Carlos L.; Giordano, Carla V.; Scopel, Ana L.; Zima, Ana M.; Szwarcberg-Bracchitta, Mariela; Searles, Peter S.; Caldwell, Martyn M.; Díaz, Susana B.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 21/12/1999 Português
Relevância na Pesquisa
454.7518%
The primary motivation behind the considerable effort in studying stratospheric ozone depletion is the potential for biological consequences of increased solar UVB (280–315 nm) radiation. Yet, direct links between ozone depletion and biological impacts have been established only for organisms of Antarctic waters under the influence of the ozone “hole;” no direct evidence exists that ozone-related variations in UVB affect ecosystems of temperate latitudes. Indeed, calculations based on laboratory studies with plants suggest that the biological impact of ozone depletion (measured by the formation of cyclobutane pyrimidine dimers in DNA) is likely to be less marked than previously thought, because UVA quanta (315–400 nm) may also cause significant damage, and UVA is unaffected by ozone depletion. Herein, we show that the temperate ecosystems of southern South America have been subjected to increasingly high levels of ozone depletion during the last decade. We found that in the spring of 1997, despite frequent cloud cover, the passages of the ozone hole over Tierra del Fuego (55° S) caused concomitant increases in solar UV and that the enhanced ground-level UV led to significant increases in DNA damage in the native plant Gunnera magellanica. The fluctuations in solar UV explained a large proportion of the variation in DNA damage (up to 68%)...

‣ Surface organization and nanopatterning of collagen by dip-pen nanolithography

Wilson, Donna L.; Martin, Raquel; Hong, Seunghun; Cronin-Golomb, Mark; Mirkin, Chad A.; Kaplan, David L.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
454.7518%
Collagen is a key fibrous protein in biological systems, characterized by a complex structural hierarchy as well as the ability to self-assemble into liquid crystalline mesophases. The structural features of collagen influence cellular responses and material properties, with importance for a wide range of biomaterials and tissue architectures. The mechanism by which fibrillar collagen structures form from liquid crystalline mesophases is not well characterized. We report positive printing of collagen and a collagen-like peptide down to 30–50-nm line widths, using the atomic force microscopy technique of dip-pen nanolithography. The method preserved the triple-helical structure and biological activity of collagen and even fostered the formation of characteristic higher levels of structural organization. The “direct-write” capability of biologically relevant molecules, while preserving their structure and functionality, provides tremendous flexibility in future biological device applications and in proteomics arrays, as well as a new strategy to study the important hierarchical assembly processes of biological systems.

‣ Sex-ratio conflicts, kin selection, and the evolution of altruism

Alonso, Wladimir J.; Schuck-Paim, Cynthia
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
454.7518%
Kin-selection theory has thrived in the explanation of a wide variety of biological phenomena, chiefly the evolution of biological altruism as that found in sterile castes of eusocial insects. Much of the way in which it has been tested is based on the existence of conflicts over sex-ratio production within eusocial colonies. However, despite neatly showing eusocial colonies as arenas where selection at the gene level triggers the appearance of sophisticated disputes, these studies have only demonstrated the existence of genes that act by biasing sex ratios to promote their own spread. Here we argue that such genes depend on the social organization of the colonies where they are expressed, but that they are not, in any way, the precursors of these societies—the major implication being that unequivocal evidence that eusociality evolved through the action of kin-selected altruistic genes is still lacking. Additionally, we highlight the neglect of alternative theories on the explanation of both biological altruism and sex-ratio conflicts, and defend that the enthusiasm with the latter has, in some cases, led to its inappropriate use as a basis for the explanation of other biological characteristics of eusocial organisms, when accounts based on phylogenetic or physiological constraints are also available.