Correction to: Managing biological invasions: the cost of inaction

Biological Invasions -     

Introduction pathways of economically costly invasive alien species

Biological Invasions - Introduction pathways play a pivotal role in the success of Invasive Alien Species (IAS)—the subset of alien species that have a negative environmental and/or...     

Studies of membranotropic and fusogenic activity of two putative HCV fusion peptides

Over the past decades, membranotropic peptides such as positively charged cell-penetrating peptides (CPPs) or amphipathic antimicrobial peptides (AMPs) have received increasing interest in order to improve therapeutic agent cellular uptake.As far as we are concerned, we were interested in studying HCV fusion peptides as putative anchors. Two peptides, HCV6 and HCV7, were identified and conjugated to a fluorescent tag NBD and tested for their interaction with liposomes as model membranes. DSC and spectrofluorescence analyses demonstrate HCV7 propensity to insert or internalize in vesicles containing anionic lipids DMPG whereas no activity was observed with zwitterionic DMPC. This behavior could be explained by the peptide sequence containing a cationic arginine residue. On the contrary, HCV6 did not exhibit any membranotropic activity but was the only sequence able to induce liposomes' fusion or aggregation monitored by spectrofluorescence and DLS. This two peptides mild activity was related to their inefficient structuration in contact with membrane mimetics, which was demonstrated by CD and NMR experiments.Altogether, our data allowed us to identify two promising membrane-active peptides from E1 and E2 HCV viral proteins, one fusogenic (HCV6) and the other membranotropic (HCV7). The latter was also confirmed by fluorescence microscopy with CHO cells, indicating that HCV7 could cross the plasma membrane via an endocytosis process. Therefore, this study provides new evidences supporting the identification of HCV6 as the HCV fusion peptide as well as insights on a novel membranotropic peptide from the HCV-E2 viral protein.     

Early calcium handling imbalance in pressure overload-induced heart failure with nearly normal left ventricular ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is a common clinical syndrome associated with high morbidity and mortality. Therapeutic options are limited due to a lack of knowledge of the pathology and its evolution. We investigated the cellular phenotype and Ca²⁺ handling in hearts recapitulating HFpEF criteria. HFpEF was induced in a portion of male Wistar rats four weeks after abdominal aortic banding. These animals had nearly normal ejection fraction and presented elevated blood pressure, lung congestion, concentric hypertrophy, increased LV mass, wall stiffness, impaired active relaxation and passive filling of the left ventricle, enlarged left atrium, and cardiomyocyte hypertrophy. Left ventricular cell contraction was stronger and the Ca²⁺ transient larger. Ca²⁺ cycling was modified with a RyR2 mediated Ca²⁺ leak from the sarcoplasmic reticulum and impaired Ca²⁺ extrusion through the Sodium/Calcium exchanger (NCX), which promoted an increase in diastolic Ca²⁺. The Sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase (SERCA2a) and NCX protein levels were unchanged. The phospholamban (PLN) to SERCA2a ratio was augmented in favor of an inhibitory effect on the SERCA2a activity. Conversely, PLN phosphorylation at the calmodulin-dependent kinase II (CaMKII)-specific site (PLN-Thr17), which promotes SERCA2A activity, was increased as well, suggesting an adaptive compensation of Ca²⁺ cycling. Altogether our findings show that cardiac remodeling in hearts with a HFpEF status differs from that known for heart failure with reduced ejection fraction. These data also underscore the interdependence between systolic and diastolic “adaptations” of Ca²⁺ cycling with complex compensative interactions between Ca²⁺ handling partner and regulatory proteins.     

Three-dimensional reconstruction of the hexagonal bilayer hemoglobin of the hydrothermal vent tube worm Riftia pachyptila by cryoelectron microscopy

A frozen-hydrated specimen of the V1 hemoglobin of the hydrothermal vent tube worm Riftia pachyptila was observed in the electron microscope and subjected to three-dimensional reconstruction by the method of random conical tilt series. The 3D volume possesses a D₆ point-group symmetry. When viewed along its 6-fold axis the vertices of its upper hexagonal layer are 16° clockwise rotated compared to those of the lower layer. A central linker complex is decorated by 12 hollow globular substructures. The linker complex comprises (i) a central hexagonal toroid, (ii) two internal bracelets onto which the hollow globular substructures are built, and (iii) six structures connecting the two hexagonal layers. The hollow globular substructures, related to the dodecamers of globin chains resulting from the dissociation of the hexagonal bilayer hemoglobin, have a local pseudo 3-fold symmetry and are composed each of three elongated structures visible when the volume is displayed at high threshold. At a resolution of 36 Å, the 3D volumes of the hexagonal bilayer hemoglobins of Riftia pachyptyla and of the leech Macrobdella decora look almost perfectly identical. © 1996 Wiley-Liss, Inc.     

Improvement of protein secondary structure prediction by combination of statistical algorithms and circular dichroism.

Three different approaches (propensity curve shifting, hydropathy index evaluation, and iterative attribution/cancellation of secondary structure) to the use of secondary structure percentages derived from circular dichroism measurements to improve the success rate of a protein secondary structure prediction method, without using decision constants, are described and compared. Propensity-curve shifting appears to be the best-performing approach, bearing an increase of 5.3% in the success rate of single-residue structural prediction when exact information on the secondary structure, obtained by X-ray crystallography, is employed; with information of an accuracy comparable to that obtainable by circular dichroism, the improvement stays between 3.5 and 4.9%, for a three-state prediction. Although developed with circular dichroism in mind, the method can use percentages of secondary structure obtained by any other experimental methodology from which they can be inferred, for instance Raman spectroscopy and infrared spectroscopy.     

Comparative study of the O(2), CO(2) and temperature effect on respiration between "Conference" pear cell protoplasts in suspension and intact pears

The influence of the O(2) and CO(2) concentration and the temperature on the O(2) uptake rate of cool-stored intact pears and pear cell protoplasts in suspension was compared. Protocols to isolate pear cell protoplasts from pear tissue and two methods to measure protoplast respiration have been developed. Modified Michaelis-Menten kinetics were applied to describe the effect of the O(2) and the CO(2) concentration on the O(2) uptake rate and temperature dependence was analysed with an Arrhenius equation. Both systems were described with a non-competitive type of CO(2) inhibition. Due to the inclusion of gas diffusion properties, the Michaelis-Menten constant for intact pears (2.5 mM) was significantly larger than the one for protoplasts in suspension (3 microM), which was in turn larger than the Michaelis-Menten constant obtained in mitochondrial respiration measurements described in the literature. It was calculated that only 3.6% of the total diffusion effect absorbed in the Michaelis-Menten constant for intact pears, could be attributed to intracellular gas diffusion. The number of cells per volume of tissue was counted microscopically to establish a relationship between the pear cell protoplast and intact pear O(2) uptake rate. A remarkable similarity was observed: values of 61.8 nmol kg(-1) s(-1) for protoplasts and 87.1 nmol kg(-1) s(-1) for intact pears were obtained. Also, the inhibitory effect of CO(2) on the respiration rate was almost identical for protoplasts and intact pears, suggesting that protoplast suspensions are useful for the study of other aspects of the respiration metabolism.     

Protochlorophyllide-NADP+ and protochlorophyllide- NADPH complexes and their regeneration after flash illumination in leaves and etioplast membranes of dark-grown wheat

The fast (1 min) regeneration process of the photoactive Pchlide forms after a light flash was studied in etiolated wheat leaves, and this process was simulated in vitro by incubating etioplast inner membranes of wheat with excess NADPH or NADP+. The 77 K fluorescence spectra were recorded after flash illumination, dark incubation and a subsequent flash illumination of the samples. A non-photoactive Pchlide form with an emission maximum at 650 nm was transiently detected in leaves during regeneration of a photoactive Pchlide form with an emission maximum at 654 nm. Gaussian deconvolution of fluorescence spectra of isolated membranes showed that this 650 nm form appeared in conditions of excess NADP+, as suggested in previous studies. Additionally a Pchlide form emitting at 638.5 nm was detected in the same conditions. The analysis of the spectra of leaves at different times after a flash indicated that these two non-photoactive forms are involved as intermediates in the regeneration of photoactive Pchlide. This regeneration is in correlation with the production of the Chlide form emitting at 676 nm. The results demonstrate that, in vivo, part of the NADPH:protochlorophyllide oxidoreductase is reloading with nonphotoactive Pchlide on a fast time-scale and that the 676 nm Chlide form is the released product of the phototransformation in this process.     

Protein secondary structure assignment through Voronoï tessellation

We present a new automatic algorithm, named VoTAP (Vo ronoï T essellation A ssignment P rocedure), which assigns secondary structures of a polypeptide chain using the list of α‐carbon coordinates. This program uses three‐dimensional Voronoï tessellation. This geometrical tool associates with each amino acid a Voronoï polyhedron, the faces of which unambiguously define contacts between residues. Thanks to the face area, for the contacts close together along the primary structure (low‐order contacts) a distinction is made between strong and normal ones. This new definition yields new contact matrices, which are analyzed and used to assign secondary structures. This assignment is performed in two stages. The first one uses contacts between residues close together along the primary structure and is based on data collected on a bank of 282 well‐refined nonredundant structures. In this bank, associations were made between the prints defined by these low‐order contacts and the assignments performed by different automatic methods. The second step focuses on the strand assignment and uses contacts between distant residues. Comparison with several other automatic assignment methods are presented, and the influence of resolution on the assignment is investigated. Proteins 2004. © 2004 Wiley‐Liss, Inc.