Protein osmotic pressure modulates actin filament length distribution

1.

The changes of the macromolecular osmotic pressure associated with F-actin solutions are related to the changes of the free energy of the free actin monomers.

2.

By making use of the model of Biron et al. [2006. Inter-filament attractions narrow the length distribution of actin filaments. Europhys. Lett. 73, 464-470], the changes of the free energy of the free actin monomers are related to the changes of the length distribution of the actin filaments.

On these bases, we propose that the length distribution of the actin filaments is regulated by (a) the free energy of hydrolysis of ATP and (b) the macromolecular osmotic pressure.

a.

While the free energy of hydrolysis of ATP tends to zero, the length distribution of the actin filaments shifts from an exponential curve to a straight line parallel to the abscissa axis (i.e. the concentration of the actin filaments becomes independent of their length). In the mean time, the total energy of the actin filaments reaches a minimum.

b.

With the increase of the macromolecular osmotic pressure the free energy of the actin monomers increases and a break is introduced in the curve that describes the length distribution of the actin filaments; the break is located at the mean length of the filaments.

     

Clinical and genetic characterization of Chanarin-Dorfman syndrome

We describe the clinical features, muscle pathology features, and molecular studies of seven patients with Chanarin-Dorfman syndrome (CDS) or neutral lipid storage disease and ichthyosis (NLSDI), a multisystem triglyceride storage disease with massive accumulation of lipid droplets in muscle fibers.All patients presented with congenital ichthyosiform erythroderma, cytoplasmic lipid droplets in blood cells, mild to severe hepatomegaly, and increased serum CK levels and liver enzymes. Three patients showed muscle symptoms and three had steathorrea. Molecular analysis identified five mutations, three of which are novel.These findings expand the clinical and mutational spectrum and underline the genetic heterogeneity of this disease.     

Insensitivity of cerebral oxygen transport to oxygen affinity of hemoglobin-based oxygen carriers

The cerebrovascular effects of exchange transfusion of various cell-free hemoglobins that possess different oxygen affinities are reviewed. Reducing hematocrit by transfusion of a non-oxygen-carrying solution dilates pial arterioles on the brain surface and increases cerebral blood flow to maintain a constant bulk oxygen transport to the brain. In contrast, transfusion of hemoglobins with P50 of 4-34 Torr causes constriction of pial arterioles that offsets the decrease in blood viscosity to maintain cerebral blood flow and oxygen transport. The autoregulatory constriction is dependent on synthesis of 20-HETE from arachidonic acid. This oxygen-dependent reaction is apparently enhanced by facilitated oxygen diffusion from the red cell to the endothelium arising from increased plasma oxygen solubility in the presence of low or high-affinity hemoglobin. Exchange transfusion of recombinant hemoglobin polymers with P50 of 3 and 18 Torr reduces infarct volume from experimental stroke. Cell-free hemoglobins do not require a P50 as high as red blood cell hemoglobin to facilitate oxygen delivery.     

High content analysis of gamma-secretase activity reveals variable dominance of presenilin mutations linked to familial Alzheimer's disease

gamma-Secretase mediates the intramembranous proteolysis of amyloid precursor protein (APP), Notch and other cellular substrates and is considered a prime pharmacological target in the development of therapeutics for Alzheimer's disease (AD). We describe here an efficient, new, simple, sensitive and rapid assay to quantify gamma-secretase activity in living cells by flow cytometry using two membrane-bound fluorescent probes, APP-GFP or C99-GFP, as substrates for gamma-secretase. The principle of the assay is based on the fact that the soluble intracellular domain of GFP-tagged APP (AICD-GFP) is released from the membrane into the cytosol following gamma-secretase cleavage. Using this feature, enzymatic activity of gamma-secretase could be deduced from the extent of the membrane retention of the probe observed after plasma membrane permeabilization and washout of the cleaved fraction. By applying two well-known gamma-secretase inhibitors (DAPT and L-685,458), we validated our assay showing that the positional GFP-based probes for gamma-secretase activity behave properly when expressed in different cell lines, providing the basis for the further development of a high-throughput and high content screening for AD targeted drug discovery. Moreover, by co-expression of different familial AD-linked mutated forms of presenilin--the key component of the gamma-secretase complex--in cells devoid of any endogenous gamma-secretase, our method allowed us to evaluate in situ the contribution of different presenilin variants to the modulation of the enzyme.     

Yeast ribosomal stalk heterogeneity in vivo shown by two-photon FCS and molecular brightness analysis

The stalk of Saccharomyces cerevisiae ribosomes contains, on average, five distinct proteins, namely P0 and four acidic proteins, P1α, P1β, P2α, and P2β. Each ribosome contains only one copy of P0, but the distribution of the acidic proteins among the ribosome population in vivo has not been determined. Using two-photon fluorescence correlation spectroscopy and scanning FCS, on cells expressing EGFP-tagged P0, P1, and P2 proteins, we show, with brightness analysis, that individual yeast ribosomes in vivo are compositionally heterogeneous in regard to P1α, P1β, P2α, and P2β. These results are relevant to the hypothesis, based on in vitro studies, that the overall cellular pattern of expressed proteins can be determined by the distribution of the stalk proteins among the ribosome population.     

The phasor approach to fluorescence lifetime imaging analysis

Changing the data representation from the classical time delay histogram to the phasor representation provides a global view of the fluorescence decay at each pixel of an image. In the phasor representation we can easily recognize the presence of different molecular species in a pixel or the occurrence of fluorescence resonance energy transfer. The analysis of the fluorescence lifetime imaging microscopy (FLIM) data in the phasor space is done observing clustering of pixels values in specific regions of the phasor plot rather than by fitting the fluorescence decay using exponentials. The analysis is instantaneous since is not based on calculations or nonlinear fitting. The phasor approach has the potential to simplify the way data are analyzed in FLIM, paving the way for the analysis of large data sets and, in general, making the FLIM technique accessible to the nonexpert in spectroscopy and data analysis.     

Phase fluctuations on the micron-submicron scale in GUVs composed of a binary lipid mixture

We used a combination of imaging and fluctuation techniques to investigate the temporal evolution of gel phase domains at the onset of phase separation, as well as the correlation between domain topology and local lipid ordering in GUVs composed of a binary mixture of DPPC/DLPC 1:1. The data acquired at temperatures immediately above the transition temperature of the two lipids suggest fluctuations in the lipid organization with a lifetime <0.1 s and a characteristic length of 1.2 μm. As the temperature is decreased below the transition temperature of one of the lipids, coupling between the two leaflets of the bilayer is observed to begin within the first five minutes after the onset of phase separation. However, domains confined to only one leaflet can be found during the first 45-50 min after the onset of phase separation. Our analysis using a two-state model (liquid and gel) indicates that for the first 45-50 min from the onset of phase separation the two lipid phases do not strongly influence the phase behavior of each other on the micron-length scale. At longer times, behavior that deviates from the two-state model is observed and appears to be correlated to domain morphology.     

Endothelial adhesion receptors are recruited to adherent leukocytes by inclusion in preformed tetraspanin nanoplatforms

VCAM-1 and ICAM-1, receptors for leukocyte integrins, are recruited to cell–cell contact sites on the apical membrane of activated endothelial cells. In this study, we show that this recruitment is independent of ligand engagement, actin cytoskeleton anchorage, and heterodimer formation. Instead, VCAM-1 and ICAM-1 are recruited by inclusion within specialized preformed tetraspanin-enriched microdomains, which act as endothelial adhesive platforms (EAPs). Using advanced analytical fluorescence techniques, we have characterized the diffusion properties at the single-molecule level, nanoscale organization, and specific intradomain molecular interactions of EAPs in living primary endothelial cells. This study provides compelling evidence for the existence of EAPs as physical entities at the plasma membrane, distinct from lipid rafts. Scanning electron microscopy of immunogold-labeled samples treated with a specific tetraspanin-blocking peptide identify nanoclustering of VCAM-1 and ICAM-1 within EAPs as a novel mechanism for supramolecular organization that regulates the leukocyte integrin–binding capacity of both endothelial receptors during extravasation.     

Phosphorylation regulates the assembly of chloroplast import machinery

Chloroplast function depends on the translocation of cytosolically synthesized precursor proteins into the organelle. The recognition and transfer of most precursor proteins across the outer membrane depend on a membrane inserted complex. Two receptor components of this complex, Toc34 and Toc159, are GTPases, which can be phosphorylated by kinases present in the hosting membrane. However, the physiological function of phosphorylation is not yet understood in detail. It is demonstrated that both receptors are phosphorylated within their G-domains. In vitro, the phosphorylation of Toc34 disrupts both homo- and heterodimerization of the G-domains as determined using a phospho-mimicking mutant. In endogenous membranes this mutation or phosphorylation of the wild-type receptor disturbs the association of Toc34, but not of Toc159 with the translocation pore. Therefore, phosphorylation serves as an inhibitor for the association of Toc34 with other components of the complex and phosphorylation can now be discussed as a mechanism to exchange different isoforms of Toc34 within this ensemble.     

Evaluation of Metarhizium anisopliae (Metsch) Sorok. to target larvae and adults of Capnodis tenebrionis (L.) (Coleoptera: Buprestidae) in soil and fiber band applications

The aim of this work has been to evaluate in the laboratory the potential of entomopathogenic fungi against adults and larvae of Capnodis tenebrionis (L.) (Coleoptera: Buprestidae) through fiber band application and a potted plant bioassay with soil application, respectively. Our previous findings revealed that Metarhizium anisopliae EAMa 01/58-Su isolate was the most virulent against neonate larvae of the buprestid. In the present work, M. anisopliae EAMa 01/58-Su isolate has been also shown to be highly virulent against adult beetles by immersion in a conidial suspension; thus it was selected to accomplish our objectives. When adult beetles were stimulated to climb 100 x 200 mm non-woven commercial fiber bands impregnated with conidia of M. anisopliae EAMa 01/58-Su isolate, total mortality rates varied from 85.7% to 100.0%; whereas no significant correlation was detected between the time needed to cross the band (mean value 648.7+/-22.4s) and the time of death, with mean average survival time ranging between 10.3 and 16.0 days, compared to 28 days of the controls. Potted seedlings (5-6 months old) of cherry plum (Prunus myrobalana Lois.), a commonly used apricot rootstock, were used to study the efficacy of soil treatment with M. anisopliae EAMa 01/58-Su isolate against neonate C. tenebrionis larvae. The soil inoculation with M. anisopliae EAMa 01/58-Su isolate had a significant effect on the mean number of dead larvae recovered from the roots, with mean mortality ranging from 83.3% to 91.6%; whereas no significant differences were detected between the three fungal doses. In all cases, dead larvae found within roots exhibited external signs of fungal growth. Hence, it may be possible to use M. anisopliae EAMa 01/58-Su isolate in a biocontrol strategy targeting both adults and larvae of C. tenebrionis.