Maintaining the permeability barrier during protein trafficking at the endoplasmic reticulum membrane

2003 ◽  
Vol 31 (6) ◽  
pp. 1227-1231 ◽  
Author(s):  
A.E. Johnson
Keyword(s):  
Endoplasmic Reticulum ◽  
Small Molecule ◽  
Protein Trafficking ◽  
Molecular Mechanisms ◽  
Protein Translocation ◽  
Cellular Membrane ◽  
Permeability Barrier ◽  
Endoplasmic Reticulum Membrane ◽  
Ion Diffusion

Many proteins are translocated across or integrated into a cellular membrane without disrupting its integrity, although it is difficult to imagine how such macromolecular transmembrane movement can occur without simultaneously allowing significant small-molecule and ion diffusion across the bilayer. Recent studies have identified some molecular mechanisms that are involved in maintaining the permeability barrier of the endoplasmic reticulum membrane during co-translational protein translocation and integration. These mechanisms are both simple and direct in concept, but are operationally complex and require the co-ordinated and regulated interaction of several multicomponent complexes.

scholarly journals Targeting of the hepatitis B virus precore protein to the endoplasmic reticulum membrane: after signal peptide cleavage translocation can be aborted and the product released into the cytoplasm.

1988 ◽  
Vol 106 (4) ◽  
pp. 1093-1104 ◽  
Author(s):  
P D Garcia ◽  
J H Ou ◽  
W J Rutter ◽  
P Walter
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Translocation ◽  
Core Protein ◽  
Signal Sequence ◽  
Signal Peptidase ◽  
Amino Terminus ◽  
Endoplasmic Reticulum Membrane ◽  
Nucleic Acid Binding ◽  
Precore Region ◽  
B Virus

The major hepatitis B virus (HBV) core protein is a viral structural protein involved in nucleic acid binding. Its coding sequence contains an extension of 29 codons (the "precore" region) at the amino terminus of the protein which is present in a fraction of the viral transcripts. This region is evolutionarily conserved among mammalian and avian HBVs, suggesting it has functional importance, although at least for duck HBV it has been shown to be nonessential for replication of infectious virions. Using in vitro assays for protein translocation across the endoplasmic reticulum membrane, we found that the precore region of the HBV genome encodes a signal sequence. This signal sequence was recognized by signal recognition particle, which targeted the nascent precore protein to the endoplasmic reticulum membrane with efficiencies comparable to those of other mammalian secretory proteins. A 19-amino acid signal peptide was removed by signal peptidase on the lumenal side of the microsomal membrane, generating a protein similar to the HBV major core protein, but containing 10 additional amino acids from the precore region at its amino terminus. Surprisingly, we found that 70-80% of this signal peptidase-cleaved product was localized on the cytoplasmic side of the microsomal vesicles and was not associated with the membranes. We conclude that translocation was aborted by an unknown mechanism, then the protein disengaged from the translocation machinery and was released back into the cytoplasm. Thus, a cytoplasmically disposed protein was created whose amino terminus resulted from signal peptidase cleavage. The remaining 20-30% appeared to be completely translocated into the lumen of the microsomes. A deletion mutant lacking the carboxy-terminal nucleic acid binding domain of the precore protein was similarly partitioned between the lumen of the microsomes and the cytoplasmic compartment, indicating that this highly charged domain is not responsible for the aborted translocation. We discuss the implications of our findings for the protein translocation process and suggest a possible role in the virus life cycle.

NMR Conformational Study of the Cytoplasmic Domain of the Canine Sec61γ Protein from the Protein Translocation Pore of the Endoplasmic Reticulum Membrane

Biochemistry ◽  
1996 ◽  
Vol 35 (47) ◽  
pp. 14717-14724 ◽  
Author(s):  
Veronica Beswick ◽  
Françoise Baleux ◽  
Tam Huynh-Dinh ◽  
François Képès ◽  
Jean-Michel Neumann ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Translocation ◽  
Cytoplasmic Domain ◽  
Endoplasmic Reticulum Membrane ◽  
Conformational Study

102. CHARACTERISATION OF THE GTPase DYNAMIN THROUGHOUT MURINE SPERM MATURATION

2010 ◽  
Vol 22 (9) ◽  
pp. 20
Author(s):  
A. T. Reid ◽  
S. D. Roman ◽  
R. Aitken ◽  
B. Nixon
Keyword(s):  
Protein Trafficking ◽  
Molecular Mechanisms ◽  
Protein Translocation ◽  
Morphological Changes ◽  
Sperm Maturation ◽  
The Novel ◽  
Epididymal Maturation ◽  
Distinct Cell ◽  
Molecular Machinery

Throughout sperm maturation distinct remodelling events occur that imbue the cells with both the ability to bind the zona pellucida and undergo the acrosome reaction. Of long standing interest to our laboratory is the elucidation of the molecular mechanisms that underpin the attainment of these key functional attributes. This process begins with a complex range of morphological changes that accompany spermatogenesis, and is continued through post-testicular phases of maturation in both the male (epididymal maturation) and female (capacitation) reproductive tracts. However, among these changes only those occurring during the initial stages of spermatogenesis are intrinsically driven. The fact that the majority of sperm remodelling is extrinsically stimulated, and occurs in the absence of new protein synthesis, highlights the potential importance of processes such as intracellular protein trafficking. This has directed our focus towards the dynamin family of protein traffickers. The GTPase dynamin exists in three isoforms, namely Dnm1, Dnm2 and Dnm3 and is an integral part of the molecular machinery required for vesicle mediated protein translocation. Recent research from our laboratory has demonstrated the presence of these three isoforms in distinct, cell-specific locations during murine spermatogenesis. Immunofluorescence on mouse testis revealed that both Dnm1 and 2 are present within a region corresponding to the developing acrosome in maturing sperm, whilst Dnm3 appears to reside solely within pre-meiotic germ cells. Interestingly, Dnm1 and Dnm2 are both retained within the peri-acrosomal region of the sperm head in mature spermatozoa. Additionally, upon the induction of capacitation in vitro, staining for both Dnm1 and 2 becomes significantly reduced. Collectively these data support the novel hypothesis that dynamin not only participates in sperm remodelling events during spermatogenesis but may also have a previously unappreciated role in capacitation-associated priming of the sperm surface for interaction with the oocyte.

scholarly journals Alteration of membrane barrier in stripped rough microsomes from rat liver on incubation with GTP: its relevance to the stimulation by this nucleotide of the dolichol pathway for protein glycosylation.

1983 ◽  
Vol 97 (2) ◽  
pp. 340-350 ◽  
Author(s):  
D Godelaine ◽  
H Beaufay ◽  
M Wibo ◽  
A M Ravoet
Keyword(s):  
Endoplasmic Reticulum ◽  
Rat Liver ◽  
Protein Glycosylation ◽  
Permeability Barrier ◽  
Endoplasmic Reticulum Membrane ◽  
Uridine Diphosphate ◽  
Guanosine Diphosphate ◽  
Membrane Barrier ◽  
Dolichol Pathway ◽  
Triton X

The membrane barrier of stripped rough microsomes from rat liver is markedly altered on incubation with GTP at 37 degrees C: after 30 min the structure-linked latency of mannose-6-phosphatase was considerably reduced, and esterase and nucleoside diphosphatase were partly released into the suspension medium. This phenomenon was already maximal with 30 microM GTP and was specific for this nucleotide. Similar conditions enhance the dolichol-mediated glycosylation of protein in microsomes incubated with uridine diphosphate N-acetylglucosamine and guanosine diphosphate mannose (Godelaine, D., H. Beaufay, M. Wibo, and A. Amar-Costesec, 1979, Eur. J. Biochem., 96:17-26; Godelaine, D., H. Beaufay, and M. Wibo, 1979, Eur. J. Biochem., 96:27-34). The GTP-induced permeability and glycosylation activities evolved in parallel in rough microsomes subjected to various treatments to detach the ribosomes and were maximal after removal of congruent to 60% of the RNA. In addition, GTP had no effect of this type in smooth microsome subfractions. Triton X-100, in spite of complex inhibitory effects on glycosylation reactions, mimicked the action of GTP by increasing the amount of microsomal dolichylphosphate that reacts with uridine diphosphate N-acetylglucosamine and by enhancing synthesis of dolichylpyrophosphoryl-chitobiose at concentrations greater than 2 mg/ml. Thus, GTP may activate dolichol-mediated glycosylation reactions in stripped microsomes by lowering the permeability barrier that prevents access of sugar nucleotides to the inner aspect of the membrane. The genuine role of GTP in the functioning of the endoplasmic reticulum membrane in situ remains unknown. Because GTP seems to act only on rough microsomes, we hypothesize that this role is somehow related to biosynthesis of protein by the rough endoplasmic reticulum.

scholarly journals The Molecular Mechanisms Underlying Mitochondria-Associated Endoplasmic Reticulum Membrane-Induced Insulin Resistance

2020 ◽  
Vol 11 ◽  
Author(s):  
Han Cheng ◽  
Xiaokun Gang ◽  
Guangyu He ◽  
Yujia Liu ◽  
Yingxuan Wang ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Insulin Signaling ◽  
Stress Responses ◽  
Molecular Mechanisms ◽  
Glucose Sensing ◽  
Hepatic Insulin Resistance ◽  
Endoplasmic Reticulum Membrane ◽  
Hepatic Insulin Signaling

Mitochondria and the endoplasmic reticulum (ER) are connected at multiple sites via what are known as mitochondria-associated ER membranes (MAMs). These associations are known to play an important role in maintaining cellular homeostasis. Impaired MAM signaling has wide-ranging effects in many diseases, such as obesity, diabetes, and neurodegenerative disorders. Accumulating evidence has suggested that MAMs influence insulin signaling through different pathways, including those associated with Ca2+ signaling, lipid metabolism, mitochondrial function, ER stress responses, and inflammation. Altered MAM signaling is a common feature of insulin resistance in different tissues, including the liver, muscle, and even the brain. In the liver, MAMs are key glucose-sensing regulators and have been proposed to be a hub for insulin signaling. Impaired MAM integrity has been reported to disrupt hepatic responses to changes in glucose availability during nutritional transition and to induce hepatic insulin resistance. Meanwhile, these effects can be rescued by the reinforcement of MAM interactions. In contrast, several studies have proposed that enhanced ER-mitochondria connections are detrimental to hepatic insulin signaling and can lead to mitochondrial dysfunction. Thus, given these contradictory results, the role played by the MAM in the regulation of hepatic insulin signaling remains elusive. Similarly, in skeletal muscle, enhanced MAM formation may be beneficial in the early stage of diabetes, whereas continuous MAM enhancement aggravates insulin resistance. Furthermore, recent studies have suggested that ER stress may be the primary pathway through which MAMs induce brain insulin resistance, especially in the hypothalamus. This review will discuss the possible mechanisms underlying MAM-associated insulin resistance as well as the therapeutic potential of targeting the MAM in the treatment of type 2 diabetes.

Sec62p, A Component of the Endoplasmic Reticulum Protein Translocation Machinery, Contains Multiple Binding Sites for the Sec-Complex

2000 ◽  
Vol 11 (11) ◽  
pp. 3859-3871 ◽  
Author(s):  
Sandra Wittke ◽  
Martin Dünnwald ◽  
Nils Johnsson
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Translocation ◽  
Signal Sequence ◽  
Endoplasmic Reticulum Membrane ◽  
Sequence Recognition ◽  
Multiple Binding Sites ◽  
Oligomeric Protein ◽  
Multiple Binding ◽  
Endoplasmic Reticulum Protein

SEC62 encodes an essential component of the Sec-complex that is responsible for posttranslational protein translocation across the membrane of the endoplasmic reticulum in Saccharomyces cerevisiae. The specific role of Sec62p in translocation was not known and difficult to identify because it is part of an oligomeric protein complex in the endoplasmic reticulum membrane. An in vivo competition assay allowed us to characterize and dissect physical and functional interactions between Sec62p and components of the Sec-complex. We could show that Sec62p binds via its cytosolic N- and C-terminal domains to the Sec-complex. The N-terminal domain, which harbors the major interaction site, binds directly to the last 14 residues of Sec63p. The C-terminal binding site of Sec62p is less important for complex stability, but adjoins the region in Sec62p that might be involved in signal sequence recognition.

scholarly journals Coordination of N-Glycosylation and Protein Translocation across the Endoplasmic Reticulum Membrane by Sss1 Protein

2003 ◽  
Vol 278 (39) ◽  
pp. 37998-38003 ◽  
Author(s):  
Wiep Scheper ◽  
Safia Thaminy ◽  
Sanja Kais ◽  
Igor Stagljar ◽  
Karin Römisch
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Translocation ◽  
Endoplasmic Reticulum Membrane
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