1,720,999 research outputs found
Pathways for glycoprotein degradation in mammalian cells
Get PDFIn mammalian cells, N-glycoproteins comprise the bulk of secretory cargo. N-glycosylation is tightly linked to the mechanisms of co- and post-translational folding and quality control in the endoplasmic reticulum (ER). Aberrant glycoproteins must be cleared from the secretory pathway. Several mechanisms for glycoprotein degradation exist, of which ER-associated degradation (ERAD) is most well-studied. The latter involves retrotranslocation of misfolded glycoproteins into the cytosol, followed by proteasomal destruction of the polypeptide. N-linked oligosaccharides are removed from glycoproteins during degradation to form free oligosaccharides (FOS). FOS analysis has been employed to gain a global, rather than single protein-centred view of the pathways of ERAD and the mechanisms of its regulation. It was established that convergent ERAD pathways, distinct in the site of deglycosylation, as well as sensitivity to a number of modulators, exist in the cell. It was further demonstrated that the pathway leading to the production of ER-localised FOS is linked to retrograde Golgi-to-ER transport and is masked by the activity of Golgi endomannosidase. Investigating the involvement on the latter in ERAD has uncovered an endomannosidase-mediated pre-degradative glycoprotein processing route and showed that endomannosidase can rescue a fraction of glycoproteins from degradation following inhibition of ER glucosidases. Further investigation of endomannosidase activity and specificity in different cell lines showed that the ability of the enzyme to process truncated monoglucosylated oligosaccharides appears to be necessary and sufficient for evolutionary conservation in mammals. Overall, the data presented have demonstrated on the global level the connections between the pathways for glycoprotein degradation and processing in the Golgi apparatus, underlining the complexity of biosynthetic regulation in the secretory pathway
Antiviral mechanisms of small molecules targeting the endoplasmic reticulum and Golgi apparatus
Get PDFN-linked glycosylation is the most common form of post-translational modification in nature and is essential to almost all enveloped viruses, including members of the Flaviviridae family. The host cell N-linked glycoprotein processing pathway is utilised by these viruses and as such has long been identified as a potential target for the development of antiviral drugs. Here, the antiviral mechanisms of three classes of small molecules targeting the secretory pathway and altering viral envelope glycosylation are investigated, using the HCV surrogate model, BVDV. The antiviral activity of imino sugars, principally through α-glucosidase inhibition, is well-characterised and here, a group of novel adamantyl coupled imino sugars are investigated and demonstrated to inhibit ER α glucosidases, which correlates with their antiviral activity against BVDV. Additionally, BVDV is used to study the antiviral mechanism of action of nitazoxanide. Nitazoxanide, the parent compound of the thiazolide class of structures, is a broadly antimicrobial compound with antiviral activity against HBV, HCV, influenza, JEV and others. Here, nitazoxanide is shown to be antiviral against BVDV by inducing Ca2+ release from ATP-sensitive intracellular calcium stores, disrupting ER-Golgi trafficking and inhibiting complex glycan formation. Finally, the potential of Golgi endo-α-mannosidase as an antiviral target is explored, using the endomannosidase inhibitor glucose-isofagomine in conjunction with the imino sugar α-glucosidase inhibitor NAP-DNJ. Endomannosidase is shown to be a valid antiviral target for BVDV, both alone and in combination with α-glucosidase inhibition, and is utilised by viral glycoproteins to acquire complex glycan structure, even in the absence of α-glucosidase inhibition. Altogether, this work furthers our understanding of the varied antiviral mechanisms of small molecules targeting the secretory pathway, enhancing the search for novel antiviral drugs directed against host cell machinery
Prevention of lysosomal storage in Tay-Sachs mice treated with N- butyldeoxynojirimycin
No full textThe glycosphingolipid (GSL) lysosomal storage diseases result from the inheritance of defects in the genes encoding the enzymes required for catabolism of GSLs within lysosomes. A strategy for the treatment of these diseases, based on an inhibitor of GSL biosynthesis N-butyldeoxynojirimycin, was evaluated in a mouse model of Tay-Sachs disease. When Tay-Sachs mice were treated with N-butyldeoxynojirimycin, the accumulation of G(M2) in the brain was prevented, with the number of storage neurons and the quantity of ganglioside stored per cell markedly reduced. Thus, limiting the biosynthesis of the substrate (G(M2)) for the defective enzyme (β-hexosaminidase A) prevents GSL accumulation and the neuropathology associated with its lysosomal storage.</p
Delayed symptom onset and increased life expectancy in Sandhoff disease mice treated with N-butyldeoxynojirimycin
No full textSandhoff disease is a neurodegenerative disorder resulting from the autosomal recessive inheritance of mutations in the HEXB gene, which encodes the β-subunit of β-hexosaminidase. G(M2) ganglioside fails to be degraded and accumulates within lysosomes in cells of the periphery and the central nervous system (CNS). There are currently no therapies for the glycosphingolipid lysosomal storage diseases that involve CNS pathology, including the G(M2) gangliosidoses. One strategy for treating this and related diseases is substrate deprivation. This would utilize an inhibitor of glycosphingolipid biosynthesis to balance synthesis with the impaired rate of catabolism, thus preventing storage. One such inhibitor is N- butyldeoxynojirimycin, which currently is in clinical trials for the potential treatment of type 1 Gaucher disease, a related disease that involves glycosphingolipid storage in peripheral tissues, but not in the CNS. In this study, we have evaluated whether this drug also could be applied to the treatment of diseases with CNS storage and pathology. We therefore have treated a mouse model of Sandhoff disease with the inhibitor N- butyldeoxynojirimycin. The treated mice have delayed symptom onset, reduced storage in the brain and peripheral tissues, and increased life expectancy. Substrate deprivation therefore offers a potentially general therapy for this family of lysosomal storage diseases, including those with CNS disease.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
