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Reticulum Membrane (reticulum + membrane)

Distribution by Scientific Domains
Life Sciences71%

Kinds of Reticulum Membrane

  • endoplasmic reticulum membrane
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    Selected Abstracts

    RFT1 deficiency in three novel CDG patients,

    HUMAN MUTATION, Issue 10 2009
    Wendy Vleugels
    Abstract The medical significance of N-glycosylation is underlined by a group of inherited human disorders called Congenital Disorders of Glycosylation (CDG). One key step in the biosynthesis of the Glc3Man9GlcNAc2 -PP-dolichol precursor, essential for N-glycosylation, is the translocation of Man5GlcNAc2 -PP-dolichol across the endoplasmic reticulum membrane. This step is facilitated by the RFT1 protein. Recently, the first RFT1-deficient CDG (RFT1-CDG) patient was identified and presented a severe N-glycosylation disorder. In the present study, we describe three novel CDG patients with an RFT1 deficiency. The first patient was homozygous for the earlier reported RFT1 missense mutation (c.199C>T; p.R67C), whereas the two other patients were homozygous for the missense mutation c.454A>G (p.K152E) and c.892G>A (p.E298,K), respectively. The pathogenic character of the novel mutations was illustrated by the accumulation of Man5GlcNAc2 -PP-dolichol and by reduced recombinant DNase 1 secretion. Both the glycosylation pattern and recombinant DNase 1 secretion could be normalized by expression of normal RFT1 cDNA in the patients' fibroblasts. The clinical phenotype of these patients comprised typical CDG symptoms in addition to sensorineural deafness, rarely reported in CDG patients. The identification of additional RFT1-deficient patients allowed to delineate the main clinical picture of RFT1-CDG and confirmed the crucial role of RFT1 in Man5GlcNAc2 -PP-dolichol translocation. Hum Mutat 30:1,7, 2009. © 2009 Wiley-Liss, Inc. [source]

    Downregulation of a rheumatoid arthritis-related antigen (RA-A47) by ra-a47 antisense oligonucleotides induces inflammatory factors in chondrocytes

    JOURNAL OF CELLULAR PHYSIOLOGY, Issue 1 2003
    Takako Hattori
    Previously we have shown that the expression of RA-A47 (rheumatoid arthritis-related antigen) which is identical to HSP47, a collagen-binding chaperon, is downregulated in chondrocytes by tumor necrosis factor , (TNF,). RA-A47 was also found on the surface of chondrocytes where it is recognized as an antigen in the serum of rheumatoid arthritis (RA) patients. Its translocation to the cell surface from endoplasmic reticulum membrane where it is normally located was also enhanced by TNF,. To understand the significance of RA-A47 downregulation in chondrocytes independent from other effects of TNF,, we used an antisense oligonucleotide approach and investigated the effect of this treatment on the expression of molecules related to matrix degradation and production of growth factors for chondrocytic, endothelial, and synovial cells. Here we show that treatment of rabbit chondrocyes and human chondrosarcoma cells HCS-2/8 by ra-a47 antisense S -oligonucleotides significantly reduced the expression of ra-a47 both at mRNA and protein level. Interestingly, this TNF,-independent RA-A47 downregulation was associated with a strong induction of matrix metalloproteinase (MMP)-9 mRNA and inducible NO synthase (iNOS) mRNA. The induction of active-type MMP-9 was further detected by gelatin zymography. Under the same conditions, the release of basic fibroblast growth factor (bFGF) and connective tissue growth factor (CTGF) from HCS-2/8 cells into the conditioned medium (CM) was strongly enhanced. These effects were not a result of TNF, upregulation, since the ra-a47 antisense oligonucleotide treatment did not enhance TNF, synthesis. These observations indicate that downregulation of RA-A47 induces TNF,-independent cartilage-degrading pathways involving iNOS and MMP-9. Furthermore, the stimulation of bFGF and CTGF release from chondrocytes may stimulate the proliferation of adjacent endothelial and/or synovial cells. J. Cell. Physiol. 197: 94,102, 2003© 2003 Wiley-Liss, Inc. [source]

    Anchorage to the cytosolic face of the endoplasmic reticulum membrane: a new strategy to stabilize a cytosolic recombinant antigen in plants

    PLANT BIOTECHNOLOGY JOURNAL, Issue 6 2008
    Alessandra Barbante
    Summary The levels of accumulation of recombinant vaccines in transgenic plants are protein specific and strongly influenced by the subcellular compartment of destination. The human immunodeficiency virus protein Nef (negative factor), a promising target for the development of an antiviral vaccine, is a cytosolic protein that accumulates to low levels in transgenic tobacco and is even more unstable when introduced into the secretory pathway, probably because of folding defects in the non-cytosolic environment. To improve Nef accumulation, a new strategy was developed to anchor the molecule to the cytosolic face of the endoplasmic reticulum (ER) membrane. For this purpose, the Nef sequence was fused to the C-terminal domain of mammalian ER cytochrome b5, a long-lived, tail-anchored (TA) protein. This consistently increased Nef accumulation by more than threefold in many independent transgenic tobacco plants. Real-time polymerase chain reaction of mRNA levels and protein pulse-chase analysis indicated that the increase was not caused by higher transcript levels but by enhanced protein stability. Subcellular fractionation and immunocytochemistry indicated that Nef-TA accumulated on the ER membrane. Over-expression of mammalian or plant ER cytochrome b5 caused the formation of stacked membrane structures, as observed previously in similar experiments performed in mammalian cells; however, Nef-TA did not alter membrane organization in tobacco cells. Finally, Nef could be removed in vitro by its tail-anchor, taking advantage of an engineered thrombin cleavage site. These results open up the way to use tail-anchors to improve foreign protein stability in the plant cytosol without perturbing cellular functions. [source]

    Mutations of key hydrophobic surface residues of 11,-hydroxysteroid dehydrogenase type 1 increase solubility and monodispersity in a bacterial expression system

    PROTEIN SCIENCE, Issue 7 2009
    Alexander J. Lawson
    Abstract 11,-Hydroxysteroid dehydrogenase type 1 (11,-HSD1) is a key enzyme in the conversion of cortisone to the functional glucocorticoid hormone cortisol. This activation has been implicated in several human disorders, notably the metabolic syndrome where 11,-HSD1 has been identified as a novel target for potential therapeutic drugs. Recent crystal structures have revealed the presence of a pronounced hydrophobic surface patch lying on two helices at the C-terminus. The physiological significance of this region has been attributed to facilitating substrate access by allowing interactions with the endoplasmic reticulum membrane. Here, we report that single mutations that alter the hydrophobicity of this patch (I275E, L266E, F278E, and L279E in the human enzyme and I275E, Y266E, F278E, and L279E in the guinea pig enzyme) result in greatly increased yields of soluble protein on expression in E. coli. Kinetic analyses of both reductase and dehydrogenase reactions indicate that the F278E mutant has unaltered Km values for steroids and an unaltered or increased kcat. Analytical ultracentrifugation shows that this mutation also decreases aggregation of both the human and guinea pig enzymes, resulting in greater monodispersity. One of the mutants (guinea pig F278E) has proven easy to crystallize and has been shown to have a virtually identical structure to that previously reported for the wild-type enzyme. The human F278E enzyme is shown to be a suitable background for analyzing the effects of naturally occurring mutations (R137C, K187N) on enzyme activity and stability. Hence, the F278E mutants should be useful for many future biochemical and biophysical studies of the enzyme. [source]

    Glutathione transport in the endo/sarcoplasmic reticulum,

    BIOFACTORS, Issue 1-4 2003
    Miklós Csala
    Glutathione transport through the endo/sarcoplasmic reticulum (ER/SR) membrane might play a role in the maintenance of the thiol redox potential difference between the lumen and the cytosol. The transport of glutathione (both GSH and glutathione disulfide, GSSG) is entirely different in the ER and SR membranes. The transport measurements based on either rapid filtration or light scattering techniques revealed that the SR membrane transports glutathione much faster than the hepatic ER membrane or microsomal membranes prepared from heart or brain. The fastest transport has been measured in the membrane of muscle terminal cisternae, which is enriched in ryanodine receptor type 1 (RyR1). All the studied membranes have been found to be equally impermeable to various hydrophilic substances of similar size to glutathione, thus the glutathione transport in muscle microsomes and terminal cysternae as well as the correlation between the rate of glutathione transport and the abundance of RyR1 are specific. In both muscle microsomes and terminal cysternae, glutathione influx can be either inhibited or activated by antagonists and agonists of the ryanodine receptor, respectively, while these agents do not influence the transport of other small permeant molecules. These findings strongly suggest that the ryanodine receptor channel activity is directly associated with glutathione transport activity in the skeletal muscle sarcoplasmic reticulum membrane. [source]

    EXCITATION,CONTRACTION COUPLING FROM THE 1950s INTO THE NEW MILLENNIUM

    CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 9 2006
    AF Dulhunty
    SUMMARY 1Excitation,contraction coupling is broadly defined as the process linking the action potential to contraction in striated muscle or, more narrowly, as the process coupling surface membrane depolarization to Ca2+ release from the sarcoplasmic reticulum. 2We now know that excitation,contraction coupling depends on a macromolecular protein complex or ,calcium release unit'. The complex extends the extracellular space within the transverse tubule invaginations of the surface membrane, across the transverse tubule membrane into the cytoplasm and then across the sarcoplasmic reticulum membrane and into the lumen of the sarcoplasmic reticulum. 3The central element of the macromolecular complex is the ryanodine receptor calcium release channel in the sarcoplasmic reticulum membrane. The ryanodine receptor has recruited a surface membrane L-type calcium channel as a ,voltage sensor' to detect the action potential and the calcium-binding protein calsequestrin to detect in the environment within the sarcoplasmic reticulum. Consequently, the calcium release channel is able to respond to surface depolarization in a manner that depends on the Ca2+ load within the calcium store. 4The molecular components of the ,calcium release unit' are the same in skeletal and cardiac muscle. However, the mechanism of excitation,contraction coupling is different. The signal from the voltage sensor to ryanodine receptor is chemical in the heart, depending on an influx of external Ca2+ through the surface calcium channel. In contrast, conformational coupling links the voltage sensor and the ryanodine receptor in skeletal muscle. 5Our current understanding of this amazingly efficient molecular signal transduction machine has evolved over the past 50 years. None of the proteins had been identified in the 1950s; indeed, there was debate about whether the molecules involved were, in fact, protein. Nevertheless, a multitude of questions about the molecular interactions and structures of the proteins and their interaction sites remain to be answered and provide a challenge for the next 50 years. [source]

    Nuclear pore disassembly from endoplasmic reticulum membranes promotes Ca2+ signalling competency

    THE JOURNAL OF PHYSIOLOGY, Issue 12 2008
    Michael J. Boulware
    The functionality of the endoplasmic reticulum (ER) as a Ca2+ storage organelle is supported by families of Ca2+ pumps, buffers and channels that regulate Ca2+ fluxes between the ER lumen and cytosol. Although many studies have identified heterogeneities in Ca2+ fluxes throughout the ER, the question of how differential functionality of Ca2+ channels is regulated within proximal regions of the same organelle is unresolved. Here, we studied the in vivo dynamics of an ER subdomain known as annulate lamellae (AL), a cytoplasmic nucleoporin-containing organelle widely used in vitro to study the mechanics of nuclear envelope breakdown. We show that nuclear pore complexes (NPCs) within AL suppress local Ca2+ signalling activity, an inhibitory influence relieved by heterogeneous dissociation of nucleoporins to yield NPC-denuded ER domains competent at Ca2+ signalling. Consequently, we propose a novel generalized role for AL , reversible attenuation of resident protein activity , such that regulated AL (dis)assembly via a kinase/phosphatase cycle allows cells to support rapid gain/loss-of-function transitions in cellular physiology. [source]