Involvement of manganese peroxidase in the transformation of macromolecules from low-rank coal by Phanerochaete chrysosporium

Manganese peroxidase (Mn peroxidase) catalyses the oxidation of Mn(II) to Mn(III), a diffusible non-specific oxidant likely to be involved in the transformation of polyphenolic macromolecules from brown coal by the white-rot fungus Phanerochaete chrysosporium. We report here that solubilised macromolecules from Morwell brown coal were depolymerised by Mn(III) ions when incubated under hyperbaric O₂. However, under N₂ or air they were polymerised, suggesting that net depolymerisation by Mn(III) requires molecular oxygen to inhibit coupling of coal radicals. Coal macromolecules were also polymerised when separated by a semipermeable membrane from a culture of P. chrysosporium or from a solution of Mn peroxidase, Mn(II) and H₂O₂, probably by Mn(III) crossing the membrane. In oxygenated cultures in which Mn peroxidase␣was up-regulated by Mn(II), the extent of depolymerisation correlated with cumulative Mn peroxidase activity suggesting that Mn-peroxidase-generated Mn(III) has a central role in initial depolymerisation of coal molecules in vivo. However, mutant ME446-B17-1, which produces Mn peroxidase but not lignin peroxidase, polymerised coal macromolecules in oxygenated cultures. In sum, it appears Mn peroxidase can both polymerise and depolymerise brown coal macromolecules and that, in vivo, both hyperbaric O₂ and lignin peroxidase are also required to force net depolymerisation to products assimilable by cells. Received: 4 September 1997 / Received revision: 29 January 1998 / Accepted: 30 January 1998     

A role for fibronectin-leucine-rich transmembrane cell-surface proteins in homotypic cell adhesion

The fibronectin-leucine-rich transmembrane (FLRT) family of leucine-rich repeat (LRR) proteins is implicated in fibroblast growth factor (FGF) signalling, early embryonic development and neurite outgrowth. Here, we have analysed whether FLRTs may also function in cell adhesion. We find that FLRT proteins can physically interact and that FLRT-transfected cultured cells sort out from non-transfected cells, suggesting a change in adhesive properties. A similar sorting effect is also observed in Xenopus embryos and tissue aggregates. FLRT-mediated cell sorting is calcium dependent and substrate independent. Deletion analysis indicates that cell sorting requires the LRR domains, which are dispensable for FLRT-mediated FGF signalling. Conversely, sorting is independent of the cytoplasmic domain, which is essential for FLRT-induced signalling. Therefore, FLRT-mediated FGF signal transduction and homotypic cell sorting can be molecularly uncoupled. The results indicate that FLRT proteins have a dual role, promoting FGF signalling and modulating homotypic cell adhesion.     

Dissecting the contributions of GC content and codon usage to gene expression in the model alga Chlamydomonas reinhardtii

The efficiency of gene expression in all organisms depends on the nucleotide composition of the coding region. GC content and codon usage are the two key sequence features known to influence gene expression, but the underlying molecular mechanisms are not entirely clear. Here we have determined the relative contributions of GC content and codon usage to the efficiency of nuclear gene expression in the unicellular green alga Chlamydomonas reinhardtii. By comparing gene variants that encode an identical amino acid sequence but differ in their GC content and/or codon usage, we show that codon usage is the key factor determining translational efficiency and, surprisingly, also mRNA stability. By contrast, unfavorable GC content affects gene expression at the level of the chromatin structure by triggering heterochromatinization. We further show that mutant algal strains that permit high‐level transgene expression are less susceptible to epigenetic transgene suppression and do not establish a repressive chromatin structure at the transgenic locus. Our data disentangle the relationship between GC content and codon usage, and suggest simple strategies to overcome the transgene expression problem in Chlamydomonas.     

Combination Therapy Using Monoclonal Antibodies against Respiratory Syncytial Virus (RSV) G Glycoprotein Protects from RSV Disease in BALB/c Mice

Therapeutic options to control respiratory syncytial virus (RSV) are limited, thus development of new therapeutics is high priority. Previous studies with a monoclonal antibody (mAb) reactive to an epitope proximal to the central conserved region (CCR) of RSV G protein (mAb 131-2G) showed therapeutic efficacy for reducing pulmonary inflammation RSV infection in BALB/c mice. Here, we show a protective effect in RSV-infected mice therapeutically treated with a mAb (130-6D) reactive to an epitope within the CCR of G protein, while treatment with a mAb specific for a carboxyl G protein epitope had no effect. Combined treatment with mAbs 130-6D and 131-2G significantly decreased RSV-associated pulmonary inflammation compared to either antibody alone. The results suggest that anti-RSV G protein mAbs that react at or near the CCR and can block RSV G protein-mediated activities are effective at preventing RSV disease and may be an effective strategy for RSV therapeutic treatment.     

Statistical Comparison of Carcinogenic Effects and Dose–Response Relationships in Rats and Mice for 2,4-Toluene Diamine to those Ascribed to Toluene Diisocyanate

The U.S. National Toxicology Program (NTP) conducted 2-year bioassays of commercial grade toluene diisocyanate (TDI) (80% 2,4-TDI and 20% 2,6-TDI) and 2,4-toluene diamine (TDA) and concluded that both were carcinogenic in rodents. In the TDI study, there was an unproven but likely formation of TDA either because of flawed test-substance handling and storage conditions and/or the atypical exposure conditions employed. Although the carcinogenic responses in both studies were qualitatively similar, several statistical analyses were performed to substantiate this possibility more rigorously. Seven different statistical approaches combine to yield a robust and consistent conclusion that, if only a small fraction (approximately 5%) of the dose of TDI were hydrolyzed to TDA in the TDI study, then that would be sufficient to explain the observed carcinogenic responses in the TDI study.     

Effect of exogenous gangliosides on human neural cell division

Human neural cells in exponential growth phase were transferred to a serum-free medium and maintained for 72 hr without any detectable loss in viability. The two normal fetal cell lines (CH_I and CH_II) showed a serum-dependent cell proliferation, but the glioblastoma multiforme cells (12–18) were able to continue proliferating in this totally synthetic medium. The incorporation of [³H] thymidine into the acid-precipitable fraction of both normal and neoplastic human neural cells was assayed in the presence and the absence of exogenous gangliosides by a convenient new method. In serum-free medium, gangliosides (50 μM) inhibited the thymidine incorporation into the normal fetal cells within 24 hr and, in serum containing medium, reduced their proliferation within 48 hr. No such effects were detectable in the glioma cells. The inhibition of thymidine incorporation in the normal cells was reversible upon removal of the gangliosides. These results indicate a role of gangliosides in the postmitotic phase of normal human neural cells resulting in the regulation of cell proliferation.