Thermal acclimation of fast-growing quail exhibit decreased oxidative stress and increased muscle fiber diameters after acute heat challenges.

Many predict dire consequences of increasing temperatures, however, high temperatures in early life may aid animals during extreme thermal events later. But, underlying physiological mechanisms have not been elucidated. We examined whether developing in warmer temperatures would physiologically benefit adult quail (Coturnix coturnix japonica Temminck and Schlegel, 1849), by exploring changes in oxidative stress and muscle structure in two lines of quail– one selected for control growth and another for fast growth and after acute heat challenges. We used a factorial design to administer four treatment combinations to each line: an initial period of either heat-stress acclimation (3 hrs every other day to 37 °C) or no acclimation , and after five weeks, either a heat-stress acute challenge (8 hrs at 39 °C) or no challenge. We found that control quail had significantly higher citrate synthase activity than fast-growing quail. Fast-growing quail had higher hydroxyl scavenging capacity than control quail. Peroxyl scavenging capacity decreased in both lines after an acute heat challenge, regardless of acclimation. Finally, fast-growing quail had larger muscle fiber diameters than control quail, and acclimated birds that experienced an acute heat challenge had larger muscle fibers than those that did not experience a heat challenge. Thus, fast-growing quail may physiologically benefit from developing in warmer temperatures.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Visualization of the Target-Membrane-Inserted Fusion Protein of Semliki Forest Virus by Combined Electron Microscopy and Crystallography

AbstractSemliki Forest virus enters cells by receptor-mediated endocytosis. The acidic environment of the endosome triggers a membrane fusion reaction that is mediated by the E1 glycoprotein. During fusion, E1 rearranges from an E1/E2 heterodimer to a highly stable, membrane-inserted E1 homotrimer (E1HT). In this study, we analyzed E1HT by a combination of electron cryomicroscopy, electron crystallography of negatively stained 2D crystals, and fitting of the available X-ray structure of the monomeric E1 ectodomain into the resulting 3D reconstruction. The visualized E1HT reveals that the ectodomain has reoriented vertically and inserted the distal tip of domain II into the lipid bilayer. Our data allow the visualization of a viral fusion protein inserted in its target membrane and demonstrate that insertion is a cooperative process, resulting in rings composed of five to six homotrimers

Purification and Crystallization Reveal Two Types of Interactions of the Fusion Protein Homotrimer of Semliki Forest Virus

The fusion proteins of the alphaviruses and flaviviruses have a similar native structure and convert to a highly stable homotrimer conformation during the fusion of the viral and target membranes. The properties of the alpha- and flavivirus fusion proteins distinguish them from the class I viral fusion proteins, such as influenza virus hemagglutinin, and establish them as the first members of the class II fusion proteins. Understanding how this new class carries out membrane fusion will require analysis of the structural basis for both the interaction of the protein subunits within the homotrimer and their interaction with the viral and target membranes. To this end we report a purification method for the E1 ectodomain homotrimer from the alphavirus Semliki Forest virus. The purified protein is trimeric, detergent soluble, retains the characteristic stability of the starting homotrimer, and is free of lipid and other contaminants. In contrast to the postfusion structures that have been determined for the class I proteins, the E1 homotrimer contains the fusion peptide region responsible for interaction with target membranes. This E1 trimer preparation is an excellent candidate for structural studies of the class II viral fusion proteins, and we report conditions that generate three-dimensional crystals suitable for analysis by X-ray diffraction. Determination of the structure will provide our first high-resolution views of both the low-pH-induced trimeric conformation and the target membrane-interacting region of the alphavirus fusion protein

Differential Cholesterol Binding by Class II Fusion Proteins Determines Membrane Fusion Properties▿

The class II fusion proteins of the alphaviruses and flaviviruses mediate virus infection by driving the fusion of the virus membrane with that of the cell. These fusion proteins are triggered by low pH, and their structures are strikingly similar in both the prefusion dimer and the postfusion homotrimer conformations. Here we have compared cholesterol interactions during membrane fusion by these two groups of viruses. Using cholesterol-depleted insect cells, we showed that fusion and infection by the alphaviruses Semliki Forest virus (SFV) and Sindbis virus were strongly promoted by cholesterol, with similar sterol dependence in laboratory and field isolates and in viruses passaged in tissue culture. The E1 fusion protein from SFV bound cholesterol, as detected by labeling with photocholesterol and by cholesterol extraction studies. In contrast, fusion and infection by numerous strains of the flavivirus dengue virus (DV) and by yellow fever virus 17D were cholesterol independent, and the DV fusion protein did not show significant cholesterol binding. SFV E1 is the first virus fusion protein demonstrated to directly bind cholesterol. Taken together, our results reveal important functional differences conferred by the cholesterol-binding properties of class II fusion proteins

Conformational change and protein-protein interactions of the fusion protein of Semliki Forest virus

International audienceFusion of biological membranes is mediated by specific lipid- interacting proteins that induce the formation and expansion of an initial fusion pore. Here we report the crystal structure of the ectodomain of the Semliki Forest virus fusion glycoprotein E1 in its low- pH- induced trimeric form. E1 adopts a folded- back conformation that, in the final post- fusion form of the full- length protein, would bring the fusion peptide loop and the transmembrane anchor to the same end of a stable protein rod. The observed conformation of the fusion peptide loop is compatible with interactions only with the outer leaflet of the lipid bilayer. Crystal contacts between fusion peptide loops of adjacent E1 trimers, together with electron microscopy observations, suggest that in an early step of membrane fusion, an intermediate assembly of five trimers creates two opposing nipple- like deformations in the viral and target membranes, leading to formation of the fusion pore