New cationic lipids form channel-like pores in phospholipid bilayers

Two representatives of a new class of cationic lipids were found to have high pore-forming activity in planar bilayer membranes. These molecules, called BHHD-TADC and BHTD-TADC, have qualitatively similar effects on phospholipid membranes. Addition of 2.5-5 micro M of either of them to the membrane bathing solutions resulted in formation of long-lived anion-selective pores with conductance in the range 0.1-2 nS in 0.1 M KCl. Pore formation was found to be dependent on the potential applied to the membrane. When negative potential was applied to membrane at the side of addition, the rate of pore formation was much lower compared to when the positive potential was applied. Dependence of pore formation on compound concentration was highly nonlinear, indicating that this process requires assembly of molecules in the membrane. Addition of any of these compounds on both sides of the membrane increased the efficiency of pore formation by one to two orders of magnitude. Pore formation was strongly pH dependent. Although pores were formed with high efficiency at pH 6.5, only occasional fluctuations of membrane conductance were observed at pH 7.5. Possible mechanisms of new compounds biological activity are discussed.     

Clinical large intestinal coccidiosis in camels (Camelus dromedarius) in the United Arab Emirates: description of lesions,endogenous stages,and redescription of Isospora orlovi,Tsygankov, 1950 oocysts

Between January and March 2001, eight 4- to 8-wk-old camels (Camelus dromedarius) from 2 farms from Dubai area of the United Arab Emirates were submitted for necropsy examination. The camels had diarrhea of 2-5 days duration. Grossly, a severe diphtheroid-to-hemorrhagic colitis was seen in all animals. Gamonts, unsporulated oocysts, sporulating oocysts, and fully sporulated oocysts were present in the intestinal epithelium and the lamina propria. Fully sporulated oocysts contained 2 sporocysts and 4 sporozoites in each sporocyst. Oocysts from fecal samples resembled oocysts of Isospora orlovi. This is the first report of an isosporan parasite associated with hemorrhagic enteritis in the large intestine of any animal.     

Mechanisms of arsenic hyperaccumulation in Pteris vittata. Uptake kinetics,interactions with phosphate,and arsenic speciation

The mechanisms of arsenic (As) hyperaccumulation in Pteris vittata, the first identified As hyperaccumulator, are unknown. We investigated the interactions of arsenate and phosphate on the uptake and distribution of As and phosphorus (P), and As speciation in P. vittata. In an 18-d hydroponic experiment with varying concentrations of arsenate and phosphate, P. vittata accumulated As in the fronds up to 27,000 mg As kg(-1) dry weight, and the frond As to root As concentration ratio varied between 1.3 and 6.7. Increasing phosphate supply decreased As uptake markedly, with the effect being greater on root As concentration than on shoot As concentration. Increasing arsenate supply decreased the P concentration in the roots, but not in the fronds. Presence of phosphate in the uptake solution decreased arsenate influx markedly, whereas P starvation for 8 d increased the maximum net influx by 2.5-fold. The rate of arsenite uptake was 10% of that for arsenate in the absence of phosphate. Neither P starvation nor the presence of phosphate affected arsenite uptake. Within 8 h, 50% to 78% of the As taken up was distributed to the fronds, with a higher translocation efficiency for arsenite than for arsenate. In fronds, 49% to 94% of the As was extracted with a phosphate buffer (pH 5.6). Speciation analysis using high-performance liquid chromatography-inductively coupled plasma mass spectroscopy showed that >85% of the extracted As was in the form of arsenite, and the remaining mostly as arsenate. We conclude that arsenate is taken up by P. vittata via the phosphate transporters, reduced to arsenite, and sequestered in the fronds primarily as As(III).     

Action spectrum for cryptochrome-dependent hypocotyl growth inhibition in Arabidopsis

Cryptochrome blue-light photoreceptors are found in both plants and animals and have been implicated in numerous developmental and circadian signaling pathways. Nevertheless, no action spectrum for a physiological response shown to be entirely under the control of cryptochrome has been reported. In this work, an action spectrum was determined in vivo for a cryptochrome-mediated high-irradiance response, the blue-light-dependent inhibition of hypocotyl elongation in Arabidopsis. Comparison of growth of wild-type, cry1cry2 cryptochrome-deficient double mutants, and cryptochrome-overexpressing seedlings demonstrated that responsivity to monochromatic light sources within the range of 390 to 530 nm results from the activity of cryptochrome with no other photoreceptor having a significant primary role at the fluence range tested. In both green- and norflurazon-treated (chlorophyll-deficient) seedlings, cryptochrome activity is fairly uniform throughout its range of maximal response (390-480 nm), with no sharply defined peak at 450 nm; however, activity at longer wavelengths was disproportionately enhanced in CRY1-overexpressing seedlings as compared with wild type. The action spectrum does not correlate well with the absorption spectra either of purified recombinant cryptochrome photoreceptor or to that of a second class of blue-light photoreceptor, phototropin (PHOT1 and PHOT2). Photoreceptor concentration as determined by western-blot analysis showed a greater stability of CRY2 protein under the monochromatic light conditions used in this study as compared with broad band blue light, suggesting a complex mechanism of photoreceptor activation. The possible role of additional photoreceptors (in particular phytochrome A) in cryptochrome responses is discussed.     

Post-translational modification detection using metastable ions in reflector matrix-assisted laser desorption/ionization-time of flight mass spectrometry

In addition to protein identification, characterization of post-translational modifications (PTMs) is an essential task in proteomics. PTMs represent the major reason for the variety of protein isoforms and they can influence protein structure and function. Upon matrix-assisted laser desorption/ionization (MALDI) most post-translationally modified peptides form a fraction of labile molecular ions, which lose PTM-specific residues only after acceleration. Compared to fully accelerated ions these fragment ions are defocused and show in reflector mass spectra reduced resolution. A short time Fourier transform using a Hanning window function now uses this difference in resolution to detect the metastable fragments. Its application over the whole mass range yields frequency distributions and amplitudes as a function of mass, where an increased low frequency proportion is highly indicative for metastable fragments. Applications on the detection of metastable losses originating from carboxamidomethylated cysteines, oxidized methionines, phosphorylated and glycosylated amino acid residues are presented. The metastable loss of mercaptoacetamide detected with this procedure represents a new feature and its integration in search algorithms will improve the specificity of MALDI peptide mass fingerprinting.     

Complement resistance is essential for colonization of the digestive tract of Hirudo medicinalis by Aeromonas strains

From the crop of the medicinal leech, Hirudo medicinalis, only Aeromonas veronii bv. sobria can be cultured consistently. Serum-sensitive A. veronii mutants were unable to colonize H. medicinalis, indicating the importance of the mammalian complement system for this unusual simplicity. Complementation of one selected mutant restored its ability to colonize. Serum-sensitive mutants are the first mutant class with a colonization defect for this symbiosis.     

Repetitive versus monomeric antigen presentation: direct visualization of antibody affinity and specificity

The concept of presenting antigens in a repetitive array to obtain high titers of specific antibodies is increasingly applied by using surface-engineered viruses or bacterial envelopes as novel vaccines. A case for this concept was made 25 years ago, when producing high-titer antisera against ordered arrays of gp23, the major capsid protein of bacteriophage T4 (Aebi et al., Proc. Natl. Acad. Sci. USA, 74 (1977) 5514-5518). In view of the current interest in this concept we thought it useful to employ this system to directly visualize the dependence of antibody affinity and specificity on antigen presentation. We compared antibodies raised against T4 polyheads, a tubular variant of the bacteriophage T4 capsid, which have gp23 hexamers arranged in a crystalline lattice (gp23(repetitive)), with those raised against the hexameric gp23 subunits (gp23(monomeric)). The labeling patterns of Fab-fragments prepared from these antibodies when bound to polyheads were determined by electron microscopy and image enhancement. Anti-gp23(repetitive) bound in a monospecific, stoichiometric fashion to the gp23 units constituting the polyhead surface. In contrast, anti-gp23(monomeric) decorated the polyhead surface randomly and with a 40-fold lower occupancy. These results concur with the difference in titers established by ELISA for the antisera against the repetitively displayed form of antigen (anti-gp23(repetitive)) and the randomly presented antigen (gp23(monomeric)), and they constitute a compelling visual documentation of the concept of repetitive antigen presentation to elicite a serotype-like immune response.     

CD4+CD25+ regulatory T cells preserve graft-versus-tumor activity while inhibiting graft-versus-host disease after bone marrow transplantation

Mature donor T cells cause graft-versus-host disease (GVHD), but they are also the main mediators of the beneficial graft-versus-tumor (GVT) activity of allogeneic bone marrow transplantation. Suppression of GVHD with maintenance of GVT activity is a desirable outcome for clinical transplantation. We have previously shown that donor-derived CD4+CD25+ regulatory T cells inhibit lethal GVHD after allogeneic bone marrow transplantation across major histocompatibility complex (MHC) class I and II barriers in mice. Here we demonstrate that in host mice with leukemia and lymphoma, CD4+CD25+ regulatory T cells suppress the early expansion of alloreactive donor T cells, their interleukin-2-receptor (IL-2R) alpha-chain expression and their capacity to induce GVHD without abrogating their GVT effector function, mediated primarily by the perforin lysis pathway. Thus, CD4+CD25+ T cells are potent regulatory cells that can separate GVHD from GVT activity mediated by conventional donor T cells.