Solar Models of Low Neutrino-Counting Rate: The Depleted Maxwellian Tail

Evolutionary sequences for the sun are presented which confirm that the Cl-37 neutrino counting rate will be greatly reduced if the high-energy tail of the Maxwellian distribution of relative energies is progressively depleted. Thermonuclear reaction rates and pressure are reevaluated for a distribution function modified by the correction factor suggested by Clayton (1974), and the effect of the results on solar models calculated with a simple Henyey code is discussed. It is shown that if the depletion is characterized by a certain exponential dependence on the distribution function, the counting rate will fall below 1 SNU for a distribution function of not less than 0.01. Suggestions are made for measuring the distribution function in the sun by means of neutrino spectroscopy and photography

Solar Models of Low Neutrino-Counting Rate: The Central Black Hole

Partial evolutionary sequences have been calculated for several solar models with central black holes of the order of one hundred-thousandth of a solar mass. If these are assumed to radiate their Eddington-limiting luminosity, the central temperature is depressed to the extent that the predicted count rate for the Cl-36 solar neutrino experiment nears the current upper limit of 1 SNU. This occurs when the auxiliary energy source provides about half of the solar luminosity. Count rates below this limit would result from an even larger black-hole luminosity. Consequences for stellar evolution of the occasional presence of black holes inside normal stars are discussed

Recognition of carbohydrate by major histocompatibility complex class I-restricted, glycopeptide-specific cytotoxic T lymphocytes

6 pages, 5 figures.-- PMID: 8046349 [PubMed].-- PMCID: PMC2191607.Cytotoxic T cells (CTL) recognize short peptide epitopes presented by class I glycoproteins encoded by the major histocompatibility complex (MHC). It is not yet known whether peptides containing posttranslationally modified amino acids can also be recognized by CTL. To address this issue, we have studied the immunogenicity and recognition of a glycopeptide carrying an O-linked N-acetylglucosamine (GlcNAc) monosaccharide-substituted serine residue. This posttranslational modification is catalyzed by a recently described cytosolic glycosyltransferase. We show that glycosylation does not affect peptide binding to MHC class I and that glycopeptides can elicit a strong CTL response that is glycopeptide specific. Furthermore, glycopeptide recognition by cytotoxic T cells is dependent on the chemical structure of the glycan as well as its position within the peptide.We wish to thank Dr. Elena Sadovnikova and Dr. Hans J. Stanss (Imperial Cancer Research Foundation, London, UK) for their valuable help with raising antipeptide CTLs; and Professor Jens Chr. Jensenius (University of Aarbus, Denmark) for helpful discussions. J. S. Haurum is a Carlsberg-Wellcome Travelling Research Fellow, G. Asequell is an EC Fellow, and A. C. Lellouch is supported by a United States Public Health Service National Research Service Award F32 GM- 15811. This work was supported by the Carlsberg Foundation, the Wellcome trust, the Beckett Foundation, and Statens Sundhedsvidenskabelige Forskningsr~d, Denmark.Peer reviewe

Glycosylation of a CNS-specific extracellular matrix glycoprotein, tenascin-R, is dominated by O-linked sialylated glycans and "brain-type” neutral N-glycans

As a member of the tenascin family of extracellular matrix glycoproteins, tenascin-R is located exclusively in the CNS. It is believed to play a role in myelination and axonal stabilization and, through repulsive properties, may contribute to the lack of regeneration of CNS axons following damage. The contrary functions of the tenascins have been localized to the different structural domains of the protein. However, little is known concerning the influence of the carbohydrate conjugated to the many potential sites for N- and O-glycosylation (10-120% by weight). As a first analytical requirement, we show that >80% of the N-glycans in tenascin-R are neutral and dominated by complex biantennary structures. These display the "brain-type” characteristics of outer-arm- and core-fucosylation, a bisecting N-acetylglucosamine and, significantly, an abundance of antennae truncation. In some structures, truncation resulted in only a single mannose residue remaining on the 3-arm, a particularly unusual consequence of the N-glycan processing pathway. In contrast to brain tissue, hybrid and oligomannosidic N-glycans were either absent or in low abundance. A high relative abundance of O-linked sialylated glycans was found. This was associated with a significant potential for O-linked glycosylation sites and multivalent display of the sialic acid residues. These O-glycans were dominated by the disialylated structure, NeuAcα2-3Galβ1-3(NeuAcα2-6)GalNAc. The possibility that these O-glycans enable tenascin-R to interact in the CNS either with the myelin associated glycoprotein or with sialoadhesin on activated microglia is discusse

A human embryonic kidney 293T cell line mutated at the Golgi -mannosidase II locus

Disruption of Golgi -mannosidase II activity can result in type II congenital dyserythropoietic anemia and can induce lupus-like autoimmunity in mice. Here, we isolate a mutant human embryonic kidney (HEK) 293T cell line, called Lec36, that displays sensitivity to ricin that lies between the parental HEK 293T cells, whose secreted and membrane-expressed proteins are dominated by complex-type glycosylation, and 293S Lec1 cells, which only produce oligomannose-type N-linked glycans. The stem cell marker, 19A, was transiently expressed in the HEK 293T Lec36 cells, and in parental HEK 293T cells with and without the potent Golgi -mannosidase II inhibitor, swainsonine. Negative-ion nano-electrospray ionization mass spectra of the 19A N-linked glycans from HEK 293T Lec36 and swainsonine-treated HEK 293T cells were qualitatively indistinguishable and, as shown by collision-induced dissociation spectra, dominated by hybrid-type glycosylation. Nucleotide sequencing revealed mutations in each allele of MAN2A1, the gene encoding Golgi -mannosidase II: a point mutation in one allele mapping to the active site and an in-frame deletion of twelve-nucleotides in the other. Expression of wild-type but not the mutant MAN2A1 alleles in Lec36 cells restored processing of the 19A reporter glycoprotein to complex-type glycosylation. The Lec36 cell line will be useful for expressing therapeutic glycoproteins with hybrid-type glycans and provides a sensitive host for detecting mutations in human MAN2A1 causing type II congenital dyserythropoietic anemia

Inhibition of Host ER Glucosidase Activity Prevents Golgi Processing of Virion-Associated Bovine Viral Diarrhea Virus E2 Glycoproteins and Reduces Infectivity of Secreted Virions

AbstractRecently, it was shown that replication of bovine viral diarrhea virus (BVDV) is sensitive to inhibitors of host ER glucosidases. Consistent with these findings, we report that incubation of BVDV-infected MDBK cells with the glucosidase inhibitor n-butyl-deoxynojirimycin (nB-DNJ) reduced BVDV yields by 70- to 100-fold (n = 27), while having no effect on MDBK cell viability. However, the 70- to 100-fold reduction in infectious virus was associated with only a 2-fold reduction in genomic RNA synthesis and secretion of enveloped virus particles. Analysis of secreted virions showed that in the absence of glucosidase inhibitor, approximately 50% of the virion-associated BVDV E2 glycoprotein was resistant to endoglycosidase H (endo H) digestion, whereas intracellular E2 was completely sensitive to endo H digestion. In the presence of glucosidase inhibitor, virion-associated E2 and intracellular E2 were completely sensitive to endo H digestion. Taken together, these results suggest that BVDV is secreted through a Golgi-mediated pathway and that host ER glucosidase activity is required for production of infectious virions and Golgi processing of envelope E2 protein during virus egress