A new method for evaluation of cavitation near mechanical heart valves

Evaluation of cavitation in vivo is often based on recordings of high-pass filtered random high-frequency pressure fluctuations. We hypothesized that cavitation signal components are more appropriately assessed by a new method for extraction of random signal components of the pressure signals. We investigated three different valve types and found a high correlation between the two methods (r2: 0.8806-0.9887). The new method showed that the cavitation signal could be extracted without a priori knowledge needed for setting the high-pass filter cut off frequency, nor did it introduce bandwidth limitation of the cavitation signal.     

Developmental control of cell morphogenesis: a focus on membrane growth

To date, the role of transport and insertion of membrane in the control of membrane remodelling during cell and tissue morphogenesis has received little attention. In contrast, the contributions of cytoskeletal rearrangements and both intercellular and cell-substrate attachments have been the focus of many studies. Here, we review work from many developmental systems that highlights the importance of polarized membrane growth and suggests a general model for the role of endocytic recycling during cell morphogenesis. We also address how the spatio-temporal control of membrane insertion during development can account for various classes of tissue rearrangements. We suggest that tubulogenesis, tissue spreading and cell intercalation stem mostly from a remarkably small number of cell intrinsic surface remodelling events that confer on cells different modes of migratory behaviours.     

P. falciparum: merozoite surface protein-8 peptides bind specifically to human erythrocytes

This work determined Plasmodium falciparum merozoite surface protein-8 (MSP-8) regions specifically binding to membrane surface receptors on human erythrocytes. Five high activity binding peptides (HABPs), whose binding to erythrocytes became saturable and sensitive on being treated with neuraminidase and chymotrypsin were identified from the MSP-8 protein. Those amino acids directly involved in interaction with erythrocytes were also determined for each one of the HABPs. Some of them specifically recognized 28, 46, and 73 kDa erythrocyte membrane proteins. Some HABPs inhibited in vitro P. falciparum merozoite invasion of erythrocytes by up to 98%, suggesting the MSP-8 protein's possible role in the invasion process.     

Reexamination of the recognition preference of the specificity pocket of the Abl SH3 domain

Src homology-3 (SH3) domains mediate important protein-protein interactions in a variety of normal and pathological cellular processes, thus providing an attractive target for the selective interference of SH3-dependent signaling events that govern these processes. Most SH3 domains recognize proline-rich peptides with low affinity and poor selectivity, and the goal to design potent and specific ligands for various SH3 domains remains elusive. Better understanding of the molecular basis for SH3 domain recognition is needed in order to design such ligands with potency and specificity. In this report, we seek to define a clear recognition preference of the specificity pocket of the Abl SH3 domain using targeted synthetic peptide libraries. High-resolution affinity panning coupled with mass spectrometric readout allows for quick identification of Trp as the preferred fourth residue in the decapeptide ligand APTWSPPPPP, which binds to Abl SH3 four times stronger than does the decapeptide containing Tyr or Phe in the fourth position. This finding is in contrast to several reports that Tyr is the only residue selected from phage displayed peptide libraries that interacts with the specificity pocket of Abl SH3. This simple, unbiased approach can fine-tune the affinity and selectivity of both natural and unnatural SH3 ligands whose consensus binding sequence has been pre-defined by combinatorial library methods.     

In-vivo glutathione elevation protects against hydroxyl free radical-induced protein oxidation in rat brain

Glutathione deficiency has been associated with a number of neurodegenerative diseases including Lou Gehrig's disease, Parkinson's disease, and HIV. A crucial role for glutathione is as a free radical scavenger. Alzheimer's disease (AD) brain is characterized by oxidative stress, manifested by protein oxidation, lipid oxidation, oxidized glutathione, and decreased activity of glutathione S-transferase, among others. Reasoning that elevated levels of endogenous glutathione would offer protection against free radical-induced oxidative stress, rodents were given in vivo injections of N-acetylcysteine (NAC), a known precursor of glutathione, to study the vulnerability of isolated synaptosomal membranes treated with Fe2+/H2O2, a known hydroxyl free radical producer. Protein carbonyls, a marker of protein oxidation, were measured. NAC significantly increased endogenous glutathione levels in cortical synaptosome cytosol (P < 0.01). As reported previously, protein carbonyl levels of the Fe2+/H2O2-treated synaptosomes were significantly higher compared to that of non-treated controls (P < 0.01), consistent with increased oxidative stress. In contrast, protein carbonyl levels in Fe2+/H2O2-treated synaptosomes isolated from NAC-injected animals were not significantly different from saline-injected non-treated controls, demonstrating protection against hydroxyl radical induced oxidative stress. These results are consistent with the notion that methods to increase endogenous glutathione levels in neurodegenerative diseases associated with oxidative stress, including AD, may be promising.     

Bacterial SLH domain proteins are non-covalently anchored to the cell surface via a conserved mechanism involving wall polysaccharide pyruvylation

Several bacterial proteins are non-covalently anchored to the cell surface via an S-layer homology (SLH) domain. Previous studies have suggested that this cell surface display mechanism involves a non-covalent interaction between the SLH domain and peptidoglycan-associated polymers. Here we report the characterization of a two-gene operon, csaAB, for cell surface anchoring, in Bacillus anthracis. Its distal open reading frame (csaB) is required for the retention of SLH-containing proteins on the cell wall. Biochemical analysis of cell wall components showed that CsaB was involved in the addition of a pyruvyl group to a peptidoglycan-associated polysaccharide fraction, and that this modification was necessary for binding of the SLH domain. The csaAB operon is present in several bacterial species that synthesize SLH-containing proteins. This observation and the presence of pyruvate in the cell wall of the corresponding bacteria suggest that the mechanism described in this study is widespread among bacteria.     

Molecular organization of the alkali-insoluble fraction of Aspergillus fumigatus cell wall

Physical and biological properties of the fungal cell wall are determined by the composition and arrangement of the structural polysaccharides. Cell wall polymers of fungi are classically divided into two groups depending on their solubility in hot alkali. We have analyzed the alkali-insoluble fraction of the Aspergillus fumigatus cell wall, which is the fraction believed to be responsible for fungal cell wall rigidity. Using enzymatic digestions with recombinant endo-beta-1,3-glucanase and chitinase, fractionation by gel filtration, affinity chromatography with immobilized lectins, and high performance liquid chromatography, several fractions that contained specific interpolysaccharide covalent linkages were isolated. Unique features of the A. fumigatus cell wall are (i) the absence of beta-1,6-glucan and (ii) the presence of a linear beta-1, 3/1,4-glucan, never previously described in fungi. Galactomannan, chitin, and beta-1,3-glucan were also found in the alkali-insoluble fraction. The beta-1,3-glucan is a branched polymer with 4% of beta-1,6 branch points. Chitin, galactomannan, and the linear beta-1, 3/1,4-glucan were covalently linked to the nonreducing end of beta-1, 3-glucan side chains. As in Saccharomyces cerevisiae, chitin was linked via a beta-1,4 linkage to beta-1,3-glucan. The data obtained suggested that the branching of beta-1,3-glucan is an early event in the construction of the cell wall, resulting in an increase of potential acceptor sites for chitin, galactomannan, and the linear beta-1,3/1,4-glucan.     

Three classes of ubiquinone analogs regulate the mitochondrial permeability transition pore through a common site

To identify the structural features required for regulation of the mitochondrial permeability transition pore (PTP) by ubiquinone analogs (Fontaine, E., Ichas, F., and Bernardi, P. (1998) J. Biol. Chem. 40, 25734-25740), we have carried out an analysis with quinone structural variants. We show that three functional classes can be defined: (i) PTP inhibitors (ubiquinone 0, decylubiquinone, ubiquinone 10, 2,3-dimethyl-6-decyl-1,4-benzoquinone, and 2,3,5-trimethyl-6-geranyl-1,4-benzoquinone); (ii) PTP inducers (2,3-dimethoxy-5-methyl-6-(10-hydroxydecyl)-1,4-benzoquinone and 2,5-dihydroxy-6-undecyl-1,4-benzoquinone); and (iii) PTP-inactive quinones that counteract the effects of both inhibitors and inducers (ubiquinone 5 and 2,3,5-trimethyl-6-(3-hydroxyisoamyl)-1,4-benzoquinone) . The structure-function correlation indicates that minor modifications in the isoprenoid side chain can turn an inhibitor into an activator, and that the methoxy groups are not essential for the effects of quinones on the PTP. Since the ubiquinone analogs used in this study have a similar midpoint potential and decrease mitochondrial production of reactive oxygen species to the same extent, these results support the hypothesis that quinones modulate the PTP through a common binding site rather than through oxidation-reduction reactions. Occupancy of this site can modulate the PTP open-closed transitions, possibly through secondary changes of the PTP Ca(2+) binding affinity.     

Dynamic changes in the gonadotrope cell subpopulations during an estradiol-induced surge in the ewe

Whether estradiol targets a subpopulation of gonadotrope cells was investigated in this study. Ovariectomized ewes (OVX) or OVX ewes immunized against GnRH and treated with hourly pulses of GnRH analogue (OVX-IMG) were killed at 6, 12, 16, and 24 h after administration of 50 microg of 17beta-estradiol (E(2)). Control ewes received no E(2) treatment. In OVX or OVX-IMG ewes killed 6 h after E(2) injection, a decrease in gonadotropin plasma levels was observed compared with non-E(2)-treated ewes. In contrast, a surge in gonadotropin plasma concentrations occurred in ewes killed 16 h after injection. The percentage of total immunoreactive gonadotrope cells among the pituitary cells was lower in E(2)-treated ewes compared with nontreated animals. The proportion of monohormonal LH cells was constant throughout the experiment, except at the surge peak, where it was enhanced. In the OVX ewes, the proportion of bihormonal LH/FSH cells was lower in the E(2)-treated ewes compared to the nontreated ewes (P: < 0.001), with a more pronounced decrease 16 h after E(2) injection. A slight increase occurred 12 h after E(2) injection compared with 6 h after injection (P: < 0.05). A similar pattern was observed in the OVX-IMG ewes, except at 12 h after E(2) injection, when no increase occurred. In both OVX and OVX-IMG ewes, injection of E(2) decreased FSHbeta mRNA expression but did not alter the relative levels of LHbeta mRNA. These data suggest that the negative feedback of E(2) on LH and FSH secretion mainly targets the bihormonal cells and occurs, at least in part, directly at the pituitary level. During the gonadotropin surge, the sustained FSH release from the bihormonal cells would induce a switch from bihormonal cells to monohormonal LH cells by depleting these cells of FSH.