Expression of the parasite protein Pc90 in plasma membranes of erythrocytes infected with Plasmodium chabaudi

Erythrocytes infected with the malaria parasite Plasmodium chabaudi contain the neo-protein Pc90 in their plasma membrane. We investigate origin, membrane disposition, and intraerythrocytic traffic of this Pc90. Metabolic labeling of P.-infected erythrocytes, combined with cell fractionation as well as Western blot analysis and immunoprecipitation using a Pc90-recognizing monoclonal antibody, show that Pc90 is synthesized by early to mid trophozoites and is transported without any apparent processing steps to the erythrocyte membrane. Based upon the inaccessibility of Pc90 from the outside in intact erythrocytes and the water solubility of membrane-associated Pc90, it is concluded that Pc90 is localized on the cytoplasmic face of the host erythrocyte membrane. Immunoelectron microscopy using a Pc90-specific monoclonal antibody and the occurrence of soluble Pc90 in host cell cytosol indicate that the Pc90 is transported in both a 'vesicle-bound' and a 'free' form through the erythrocyte cytoplasm.     

Changes in cell-surface expression of MHC and Thy-1.2 determinants following treatment with lipid modulating agents

Treatment of normal mouse spleen cells with lipid fluidity modulators changes the expression of cell-surface H-2 determinants. BALB/c spleen cells treated for 1 to 2 hr with cholesteryl hemisuccinate (CHS) displayed reduced levels of all tested H-2 determinants (H-2L, H-2K, and H-2D) as evaluated by flow microfluorometry and increased membrane lipid packing density as determined by 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence polarization. In contrast, decreasing membrane lipid packing density by phosphatidylcholine treatment decreased DPH fluorescence polarization and increased the expression of MHC determinants. The effects were selective in that expression of Thy-1.2 determinants was decreased by the latter treatment and not increased by CHS. The results are discussed in terms of passive modulation of antigenic expression.     

Dimer Formation of a Stabilized Gβ1 Variant: A Structural and Energetic Analysis

In previous work, a strongly stabilized variant of the β1 domain of streptococcal protein G (Gβ1) was obtained by an in vitro selection method. This variant, termed Gβ1-M2, contains the four substitutions E15V, T16L, T18I, and N37L. Here we elucidated the molecular basis of the observed strong stabilizations. The contributions of these four residues were analyzed individually and in various combinations, additional selections with focused Gβ1 gene libraries were performed, and the crystal structure of Gβ1-M2 was determined. All single substitutions (E15V, T16L, T18I, and N37L) stabilize wild-type Gβ1 by contributions of between 1.6 and 6.0 kJ mol^− 1 (at 70 °C). Hydrophobic residues at positions 16 and 37 provide the major contribution to stabilization by enlarging the hydrophobic core of Gβ1. They also increase the tendency to form dimers, as shown by dependence on the concentration of apparent molecular mass in analytical ultracentrifugation, by concentration-dependent stability, and by a strongly increased van't Hoff enthalpy of unfolding. The 0.88-Å crystal structure of Gβ1-M2 and NMR measurements in solution provide the explanation for the observed dimer formation. It involves a head-to-head arrangement of two Gβ1-M2 molecules via six intermolecular hydrogen bonds between the two β strands 2 and 2′ and an adjacent self-complementary hydrophobic surface area, which is created by the T16L and N37L substitutions and a large 120° rotation of the Tyr33 side chain. This removal of hydrophilic groups and the malleability of the created hydrophobic surface provide the basis for the dimer formation of stabilized Gβ1 variants.     

Assessment of Plasmodium falciparum PfMDR1 transport rates using Fluo‐4

Mutations in the multidrug resistance transporter of Plasmodium falciparum PfMDR1 have been implicated to play a significant role in the emergence of worldwide drug resistance, yet the molecular and biochemical mechanisms of this transporter are not well understood. Although it is generally accepted that drug resistance in P. falciparum is partly associated with PfMDR1 transport activity situated in the membrane of the digestive vacuole, direct estimates of the pump rate of this transport process in the natural environment of the intact host–parasite system have never been analysed. The fluorochrome Fluo‐4 is a well‐documented surrogate substrate of PfMDR1 and has been found to accumulate by actively being transported into the digestive vacuole of several parasitic strains. In the present study, we designed an approach to use Fluo‐4 fluorescence uptake as a measure of compartmental Fluo‐4 concentration accumulation in the different compartments of the host–parasite system. We performed a ‘reverse Fluo‐4 imaging' approach to relate fluorescence intensity to changes in dye concentration rather than Ca²⁺ fluctuations and were able to calculate the overall rate of transport for PfMDR1 in Dd2 parasites. With this assay, we provide a powerful method to selectively measure the effect of PfMDR1 mutations on substrate transport kinetics. This will be of high significance for future compound screening to test for new drugs in resistant P. falciparum strains.     

Cathepsin L expression is directed to secretory vesicles for enkephalin neuropeptide biosynthesis and secretion

Proteases within secretory vesicles are required for conversion of neuropeptide precursors into active peptide neurotransmitters and hormones. This study demonstrates the novel cellular role of the cysteine protease cathepsin L for producing the (Met)enkephalin peptide neurotransmitter from proenkephalin (PE) in the regulated secretory pathway of neuroendocrine PC12 cells. These findings were achieved by coexpression of PE and cathepsin L cDNAs in PC12 cells with analyses of PE-derived peptide products. Expression of cathepsin L resulted in highly increased cellular levels of (Met)enkephalin, resulting from the conversion of PE to enkephalin-containing intermediates of 23, 18-19, 8-9, and 4.5 kDa that were similar to those present in vivo. Furthermore, expression of cathepsin L with PE resulted in increased amounts of nicotine-induced secretion of (Met)enkephalin. These results indicate increased levels of (Met)enkephalin within secretory vesicles of the regulated secretory pathway. Importantly, cathespin L expression was directed to secretory vesicles, demonstrated by colocalization of cathepsin L-DsRed fusion protein with enkephalin and chromogranin A neuropeptides that are present in secretory vesicles. In vivo studies also showed that cathepsin L in vivo was colocalized with enkephalin. The newly defined secretory vesicle function of cathepsin L for biosynthesis of active enkephalin opioid peptide contrasts with its function in lysosomes for protein degradation. These findings demonstrate cathepsin L as a distinct cysteine protease pathway for producing the enkephalin member of neuropeptides.     

Reconfigurable Boolean Logic Using Magnetic Single-Electron Transistors

We propose a novel hybrid single-electron device for reprogrammable low-power logic operations, the magnetic single-electron transistor (MSET). The device consists of an aluminium single-electron transistor with a GaMnAs magnetic back-gate. Changing between different logic gate functions is realized by reorienting the magnetic moments of the magnetic layer, which induces a voltage shift on the Coulomb blockade oscillations of the MSET. We show that we can arbitrarily reprogram the function of the device from an n-type SET for in-plane magnetization of the GaMnAs layer to p-type SET for out-of-plane magnetization orientation. Moreover, we demonstrate a set of reprogrammable Boolean gates and its logical complement at the single device level. Finally, we propose two sets of reconfigurable binary gates using combinations of two MSETs in a pull-down network.     

Specific cross-protective antigonococcal immunity in the murine genital tract

Specific acquired immunity to gonococci was studied in systemically immunized mice, challenged with 10(7) gonococci by intrauterine inoculation. Protection after intraperitoneal immunization was monitored by vaginal cultures taken 24 h post-challenge, since events during the first 24 h postexposure to gonococci are crucial in determining the outcome of infection. Mice were protected against gonococcal challenge by two inoculations with either live or boiled gonococci given 4 weeks apart, whereas immunization with one inoculation did not protect against challenge 1 week later. Protection was correlated with high titers of IgG antibody in serum after two immunizations, but not with the high titers of serum IgM antibody found after the one immunization. IgG antibodies, but not IgM antibodies, were shown to pass into genital secretions. Protection could be passively transferred by serum with high titers of antibody. Of most practical importance was the finding that not only were heat-stable antigens protective, but also heterologous protection resulted after immunization with three strains differing in source (disseminated gonococcal infection versus gonorrhea), opacity-transparency characteristics, and serum sensitivity. The data indicate that IgG antibodies resulting from systemic immunization with heat-stable antigens may be able to provide cross-protection immunity against gonorrhea.     

Proteins of bovine leudemia virus: p. 15 is the major phosphorprotein.

Sodium dodecylsulfate-polyacrylamide gel electrophoresis of bovine leukemia virus (BLV) grown in fetal lamb kidney cells in the presence of 32P-phosphoric acid showed that the slightly basic 15000 D protein (pp 15) is the major phosphorylated component of the virus. This result further distinguishes BLV from mammalian type C viruses which possess acidic major phosphorproteins.