Effects of lycorine on growth and effects of L-galactonic acid-gamma-lactone on ascorbic acid biosynthesis in strains of Cryptococcus laurentii isolated from Narcissus pseudonarcissus roots and bulbs

The alkaloid lycorine, which is considered to inhibit the last step in ascorbic acid biosynthesis, is produced by Narcissus pseudonarcissus. The growth of two strains (C1 and C3) of Cryptococcus laurentii isolated from root tips of N. pseudonarcissus is inhibited by lycorine, as is the in vivo production of ascorbic acid from -galactonic acid-γ-lactone. In contrast, C. laurentii strain C4, isolated from the lycorine-containing bracts of the bulb, was not inhibited by lycorine and did not contain ascorbic acid when cultivated with or without -galactonic acid-γ-lactone. This revised version was published online in June 2006 with corrections to the Cover Date.     

Selective excitation of native fluctuations during thermal unfolding simulations: horse heart cytochrome c as a case study

The effect of temperature on the activation of native fluctuation motions during molecular dynamics unfolding simulations of horse heart cytochrome c has been studied. Essential dynamics analysis has been used to analyze the preferred directions of motion along the unfolding trajectories obtained by high temperature simulations. The results of this study have evidenced a clear correlation between the directions of the deformation motions that occur in the first stage of the unfolding process and few specific essential motions characterizing the 300 K dynamics of the protein. In particular, one of those collective motions, involved in the fluctuation of a loop region, is specifically excited in the thermal denaturation process, becoming progressively dominant during the first 500 ps of the unfolding simulations. As further evidence, the essential dynamics sampling performed along this collective motion has shown a tendency of the protein to promptly unfold. According to these results, the mechanism of thermal induced denaturation process involves the selective excitation of one or few specific equilibrium collective motions.     

Empirical evidence for key hosts in persistence of a tick-borne disease

An important epidemiological consequence of aggregated host-parasite associations occurs when parasites are vectors of pathogens. Those hosts that attract many vectors will tend to be the focus of transmission. But to what extent, and can we identify characteristics of these key hosts? We investigated these questions with respect to the host-tick relationship of the yellow-necked mouse, Apodemus flavicollis, a critical host in the maintenance of the zoonotic disease, tick-borne encephalitis. Transmission of the virus occurs when ticks feed in a 'co-feeding' aggregation. Thus, the number and frequency of co-feeding groups provides an estimate of the potential rate of virus transmission. We recorded the spatio-temporal variations in co-feeding on a population of rodents in conjunction with recording individual host characteristics. Using Lorenz curves, we revealed conformation of tick-borne encephalitis transmission potential to the 20/80 Rule, where the 20% of hosts most infested with ticks were accountable for 80% of transmission potential. Hosts in the transmission cohort were identified as the sexually mature males of high body mass. Therefore control efforts targeted at this group would substantially reduce transmission potential compared to non-targeted control of the population, which resulted in a linear reduction in transmission potential. Focusing on the 'wrong' functional group would have little impact upon transmission potential until a considerable proportion of the population had been subject to control. However, individuals can change their functional status over time making it difficult to predict the contribution of these individuals to future transmission.     

Inactivation of the selB gene in Methanococcus maripaludis: effect on synthesis of selenoproteins and their sulfur-containing homologs

The genome of Methanococcus maripaludis harbors genes for at least six selenocysteine-containing proteins and also for homologs that contain a cysteine codon in the position of the UGA selenocysteine codon. To investigate the synthesis and function of both the Se and the S forms, a mutant with an inactivated selB gene was constructed and analyzed. The mutant was unable to synthesize any of the selenoproteins, thus proving that the gene product is the archaeal translation factor (aSelB) specialized for selenocysteine insertion. The wild-type form of M. maripaludis repressed the synthesis of the S forms of selenoproteins, i.e., the selenium-independent alternative system, in selenium-enriched medium, but the mutant did not. We concluded that free selenium is not involved in regulation but rather a successional compound such as selenocysteyl-tRNA or some selenoprotein. Apart from the S forms, several enzymes from the general methanogenic route were affected by selenium supplementation of the wild type or by the selB mutation. Although the growth of M. maripaludis on H(2)/CO(2) is only marginally affected by the selB lesion, the gene is indispensable for growth on formate because M. maripaludis possesses only a selenocysteine-containing formate dehydrogenase.     

Identification of a novel transporter for dicarboxylates and tricarboxylates in plant mitochondria. Bacterial expression, reconstitution, functional characterization, and tissue distribution

A cDNA from Arabidopsis thaliana and four related cDNAs from Nicotiana tabacum that we have isolated encode hitherto unidentified members of the mitochondrial carrier family. These proteins have been overexpressed in bacteria and reconstituted into phospholipid vesicles. Their transport properties demonstrate that they are orthologs/isoforms of a novel mitochondrial carrier capable of transporting both dicarboxylates (such as malate, oxaloacetate, oxoglutarate, and maleate) and tricarboxylates (such as citrate, isocitrate, cis-aconitate, and trans-aconitate). The newly identified dicarboxylate-tricarboxylate carrier accepts only the single protonated form of citrate (H-citrate2-) and the unprotonated form of malate (malate2-) and catalyzes obligatory, electroneutral exchanges. Oxoglutarate, citrate, and malate are mutually competitive inhibitors, showing K(i) close to the respective K(m). The carrier is expressed in all plant tissues examined and is largely spread in the plant kingdom. Furthermore, nitrate supply to nitrogen-starved tobacco plants leads to an increase in its mRNA in roots and leaves. The dicarboxylate-tricarboxylate carrier may play a role in important plant metabolic functions requiring organic acid flux to or from the mitochondria, such as nitrogen assimilation, export of reducing equivalents from the mitochondria, and fatty acid elongation.     

Nippostrongylus brasiliensis can induce B7-independent antigen-specific development of IL-4-producing T cells from naive CD4 T cells in vivo

Th2 immune responses to a number of infectious pathogens are dependent on B7-1/B7-2 costimulatory molecule interactions. We have now examined the Th2 immune response to Nippostrongylus brasiliensis (Nb) in B7-1/B7-2(-/-) mice and show that Th2 effector cells develop that can mediate worm expulsion and produce substantial Th2 cytokines comparable with wild-type infected mice; however, in marked contrast, B cell Ag-specific Ab production is abrogated after B7 blockade. To examine the mechanism of T cell activation, OVA-specific DO11.10 T cells were transferred to recipient mice, which were then immunized with a combination of Nb plus OVA or either alone. Only the combination of Nb plus OVA triggered T cell differentiation to OVA-specific Th2 cells, suggesting that Nb acts as an adjuvant to stimulate Ag-specific naive T cells to differentiate to effector Th2 cells. Furthermore, using the DO11.10 TCR-transgenic T cell adoptive transfer model, we show that blocking B7-1/B7-2 interactions does not impair nonparasite Ag-specific DO11.10 Th2 cell differentiation; however, DO11.10 T cell cycle progression and migration to the B cell zone are inhibited.     

Memory Th2 effector cells can develop in the absence of B7-1/B7-2, CD28 interactions,and effector Th cells after priming with an intestinal nematode parasite

B7-1/B7-2 interactions are required for many Th2-cell mediated primary immune responses including the response that follows infection with the intestinal nematode parasite, Heligmosomoides polygyrus. However, few studies have examined the role of B7-1/B7-2/CD28 interactions in the development of a Th2 memory immune response. We examined the development of the memory Th2 response to H. polygyrus in BALB/c mice deficient in both B7-1 and B7-2 (B7-1/B7-2(-/-)) and in BALB/c mice deficient in CD28 (CD28(-/-)). Following primary inoculation with H. polygyrus, adult worms in the gut were cleared with an anti-helminthic drug and mice were subsequently challenge-inoculated with H. polygyrus larvae. The memory Th2 response is readily distinguished by its inhibitory effect on adult worm maturation, resulting in marked reductions in adult worm egg production that are not observed during the primary immune response. Following H. polygyrus challenge inoculation, comparable decreases in egg production and similar increases in mesenteric lymph node cell IL-4 production were observed in B7-1/B7-2(-/-) and B7-1/B7-2(+/+) mice. However, elevations in total serum IgG1 and IgE were reduced, while increases in serum Ag-specific IgG1 and IgE and germinal center formation were blocked in H. polygyrus-challenged B7-1/B7-2(-/-) mice. In contrast, in H. polygyrus-challenged CD28(-/-) mice, marked elevations in Ag-specific IgG1 and IgE and increased germinal center formation were observed. The results of these studies demonstrate that effector Th2 memory cells that produce IL-4 and mediate host defense can develop when B7-1/B7-2 interactions, and associated effector Th2 cell development, are blocked during priming. However, humoral immunity is impaired and differentially affected in B7-1/B7-2(-/-) mice and CD28(-/-) mice following H. polygyrus challenge.     

HIV-1 envelope gp41 peptides promote migration of human Fc epsilon RI+ cells and inhibit IL-13 synthesis through interaction with formyl peptide receptors

We evaluated the effects of synthetic peptides (2017, 2019, 2020, 2021, 2023, 2027, 2029, 2030, 2031, and 2035) encompassing the structure of HIV-1(MN) envelope gp41 on both chemotaxis of human basophils and the release of preformed mediators (histamine) and of cytokines (IL-13). Peptides 2019 and 2021 were potent basophil chemoattractants, whereas the other peptides examined were ineffective. Preincubation of basophils with FMLP or gp41 2019 resulted in complete desensitization to a subsequent challenge with homologous stimulus. Incubation of basophils with low concentration (5 x 10(-7) M) of FMLP, which binds with high affinity to N-formyl peptide receptor (FPR), but not to FPR-like 1, did not affect the chemotactic response to a heterologous stimulus (gp41 2019). In contrast, a high concentration (10(-4) M) of FMLP, which binds also to FPR-like 1, significantly reduced the chemotactic response to gp41 2019. The FPR antagonist cyclosporin H inhibited chemotaxis induced by FMLP, but not by gp41 2019. None of these peptides singly induced the release of histamine or cytokines (IL-4 and IL-13) from basophils. However, low concentrations of peptides 2019 and 2021 (10(-8)-10(-6) M) inhibited histamine release from basophils challenged with FMLP but not the secretion caused by anti-IgE and gp120. Preincubation of basophils with peptides 2019 and 2021 inhibited the expression of both IL-13 mRNA, and the FMLP-induced release of IL-13 from basophils. These data highlight the complexity of the interactions between viral and bacterial peptides with FPR subtypes on human basophils.     

Role of cholesterol in human immunodeficiency virus type 1 envelope protein-mediated fusion with host cells

In this study we examined the effects of target membrane cholesterol depletion and cytoskeletal changes on human immunodeficiency virus type 1 (HIV-1) Env-mediated membrane fusion by dye redistribution assays. We found that treatment of peripheral blood lymphocytes (PBL) with methyl-beta-cyclodextrin (MbetaCD) or cytochalasin reduced their susceptibility to membrane fusion with cells expressing HIV-1 Env that utilize CXCR4 or CCR5. However, treatment of human osteosarcoma (HOS) cells expressing high levels of CD4 and coreceptors with these agents did not affect their susceptibility to HIV-1 Env-mediated membrane fusion. Removal of cholesterol inhibited stromal cell-derived factor-1alpha- and macrophage inflammatory protein 1beta-induced chemotaxis of both PBL and HOS cells expressing CD4 and coreceptors. The fusion activity as well as the chemotactic activity of PBL was recovered by adding back cholesterol to these cells. Confocal laser scanning microscopy analysis indicated that treatment of lymphocytes with MbetaCD reduced the colocalization of CD4 or of CXCR4 with actin presumably in microvilli. These findings indicate that, although cholesterol is not required for HIV-1 Env-mediated membrane fusion per se, its depletion from cells with relatively low coreceptor densities reduces the capacity of HIV-1 Env to engage coreceptor clusters required to trigger fusion. Furthermore, our results suggest that coreceptor clustering may occur in microvilli that are supported by actin polymerization.     

Differential inhibition of 30S and 70S translation initiation complexes on leaderless mRNA by kasugamycin

In contrast to canonical mRNAs, translation of leaderless mRNA has been previously reported to continue in the presence of the antibiotic kasugamycin. Here, we have studied the effect of the antibiotic on determinants known to affect translation of leadered and leaderless mRNAs. Kasugamycin did not affect the Shine-Dalgarno (SD)-anti-SD (aSD) interaction or the function of translation initiation factor 3 (IF3). Thus, the preferential translation of leaderless mRNA in the presence of kasugamycin can neither be attributed to an expanding pool of 30S subunits with a "blocked" aSD nor to a lack of action of IF3, which has been shown to discriminate against translation initiation at 5'-terminal start codons. Using toeprinting, we observed that on leaderless mRNA 70S in contrast to 30S translation initiation complexes are comparatively resistant to the antibiotic. These results taken together with the known preference of 70S ribosomes for 5'-terminal AUGs lend support to the hypothesis that translation of leaderless mRNAs may as well proceed via an alternative initiation pathway accomplished by intact 70S ribosomes.