scholarly journals Membrane Delivery to the Yeast Autophagosome from the Golgi–Endosomal System

2010 ◽  
Vol 21 (22) ◽  
pp. 3998-4008 ◽  
Author(s):  
Yohei Ohashi ◽  
Sean Munro
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Integral Membrane Protein ◽  
Autophagosome Formation ◽  
Endosomal System

While many of the proteins required for autophagy have been identified, the source of the membrane of the autophagosome is still unresolved with the endoplasmic reticulum (ER), endosomes, and mitochondria all having been evoked. The integral membrane protein Atg9 is delivered to the autophagosome during starvation and in the related cytoplasm-to-vacuole (Cvt) pathway that occurs constitutively in yeast. We have examined the requirements for delivery of Atg9-containing membrane to the yeast autophagosome. Atg9 does not appear to originate from mitochondria, and Atg9 cannot reach the forming autophagosome directly from the ER or early Golgi. Components of traffic between Golgi and endosomes are known to be required for the Cvt pathway but do not appear required for autophagy in starved cells. However, we find that pairwise combinations of mutations in Golgi-endosomal traffic components apparently only required for the Cvt pathway can cause profound defects in Atg9 delivery and autophagy in starved cells. Thus it appears that membrane that contains Atg9 is delivered to the autophagosome from the Golgi-endosomal system rather than from the ER or mitochondria. This is underestimated by examination of single mutants, providing a possible explanation for discrepancies between yeast and mammalian studies on Atg9 localization and autophagosome formation.

scholarly journals Autophagosome formation in relation to the endoplasmic reticulum

2020 ◽  
Vol 27 (1) ◽  
Author(s):  
Yo-hei Yamamoto ◽  
Takeshi Noda
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
De Novo ◽  
Transmembrane Protein ◽  
Lipid Transfer ◽  
Membrane Structures ◽  
Autophagosome Formation ◽  
Selective Autophagy ◽  
The Relationship ◽  
Er Membrane

Abstract Autophagy is a process in which a myriad membrane structures called autophagosomes are formed de novo in a single cell, which deliver the engulfed substrates into lysosomes for degradation. The size of the autophagosomes is relatively uniform in non-selective autophagy and variable in selective autophagy. It has been recently established that autophagosome formation occurs near the endoplasmic reticulum (ER). In this review, we have discussed recent advances in the relationship between autophagosome formation and endoplasmic reticulum. Autophagosome formation occurs near the ER subdomain enriched with phospholipid synthesizing enzymes like phosphatidylinositol synthase (PIS)/CDP-diacylglycerol-inositol 3-phosphatidyltransferase (CDIPT) and choline/ethanolamine phosphotransferase 1 (CEPT1). Autophagy-related protein 2 (Atg2), which is involved in autophagosome formation has a lipid transfer capacity and is proposed to directly transfer the lipid molecules from the ER to form autophagosomes. Vacuole membrane protein 1 (VMP1) and transmembrane protein 41b (TMEM41b) are ER membrane proteins that are associated with the formation of the subdomain. Recently, we have reported that an uncharacterized ER membrane protein possessing the DNAJ domain, called ERdj8/DNAJC16, is associated with the regulation of the size of autophagosomes. The localization of ERdj8/DNAJC16 partially overlaps with the PIS-enriched ER subdomain, thereby implying its association with autophagosome size determination.

scholarly journals Infectious Bronchitis Virus 3a Protein Localizes to a Novel Domain of the Smooth Endoplasmic Reticulum

2005 ◽  
Vol 79 (10) ◽  
pp. 6142-6151 ◽  
Author(s):  
Amanda R. Pendleton ◽  
Carolyn E. Machamer
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Infectious Bronchitis Virus ◽  
Smooth Endoplasmic Reticulum ◽  
Integral Membrane Protein ◽  
Open Reading Frames ◽  
Infectious Bronchitis ◽  
Infected Cells ◽  
Group 3 ◽  
Small Open Reading Frames

ABSTRACT All coronaviruses possess small open reading frames (ORFs) between structural genes that have been hypothesized to play important roles in pathogenesis. Infectious bronchitis virus (IBV) ORF 3a is one such gene. It is highly conserved among group 3 coronaviruses, suggesting that it has an important function in infection. IBV 3a protein is expressed in infected cells but is not detected in virions. Sequence analysis predicted that IBV 3a was a membrane protein; however, only a fraction behaved like an integral membrane protein. Microscopy and immunoprecipitation studies demonstrated that IBV 3a localized to the cytoplasm in a diffuse pattern as well as in sharp puncta in both infected and transfected cells. These puncta did not overlap cellular organelles or other punctate structures. Confocal microscopy demonstrated that IBV 3a puncta lined up along smooth endoplasmic reticulum (ER) tubules and, in a significant number of instances, were partially surrounded by these tubules. Our results suggest that IBV 3a is partially targeted to a novel domain of the smooth ER.

scholarly journals UDP-Galactose:Ceramide Galactosyltransferase Is a Class I Integral Membrane Protein of the Endoplasmic Reticulum

1998 ◽  
Vol 273 (40) ◽  
pp. 25880-25888 ◽  
Author(s):  
Hein Sprong ◽  
Boudewijn Kruithof ◽  
Richtje Leijendekker ◽  
Jan Willem Slot ◽  
Gerrit van Meer ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Integral Membrane Protein ◽  
Class I

scholarly journals Erv26p Directs Pro-Alkaline Phosphatase into Endoplasmic Reticulum–derived Coat Protein Complex II Transport Vesicles

2006 ◽  
Vol 17 (11) ◽  
pp. 4780-4789 ◽  
Author(s):  
Catherine A. Bue ◽  
Christine M. Bentivoglio ◽  
Charles Barlowe
Keyword(s):  
Alkaline Phosphatase ◽  
Endoplasmic Reticulum ◽  
Coat Protein ◽  
Membrane Protein ◽  
Protein Complex ◽  
Integral Membrane Protein ◽  
Secretory Proteins ◽  
Complex Ii ◽  
Transport Vesicles ◽  
Copii Vesicles

Secretory proteins are exported from the endoplasmic reticulum (ER) in transport vesicles formed by the coat protein complex II (COPII). We detected Erv26p as an integral membrane protein that was efficiently packaged into COPII vesicles and cycled between the ER and Golgi compartments. The erv26Δ mutant displayed a selective secretory defect in which the pro-form of vacuolar alkaline phosphatase (pro-ALP) accumulated in the ER, whereas other secretory proteins were transported at wild-type rates. In vitro budding experiments demonstrated that Erv26p was directly required for packaging of pro-ALP into COPII vesicles. Moreover, Erv26p was detected in a specific complex with pro-ALP when immunoprecipitated from detergent-solublized ER membranes. Based on these observations, we propose that Erv26p serves as a transmembrane adaptor to link specific secretory cargo to the COPII coat. Because ALP is a type II integral membrane protein in yeast, these findings imply that an additional class of secretory cargo relies on adaptor proteins for efficient export from the ER.

scholarly journals Characterization of Membrane Association Domains within the Tomato Ringspot Nepovirus X2 Protein, an Endoplasmic Reticulum-Targeted Polytopic MembraneProtein

2006 ◽  
Vol 80 (21) ◽  
pp. 10847-10857 ◽  
Author(s):  
Guangzhi Zhang ◽  
Hélène Sanfaçon
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Fluorescent Protein ◽  
Integral Membrane Protein ◽  
Protein Domain ◽  
Nucleoside Triphosphate ◽  
Sequence Motifs ◽  
Conserved Sequence ◽  
Er Targeting

ABSTRACT Replication of nepoviruses (family Comoviridae) occurs in association with endoplasmic reticulum (ER)-derived membranes. We have previously shown that the putative nucleoside triphosphate-binding protein (NTB) of Tomato ringspot nepovirus is an integral membrane protein with two ER-targeting sequences and have suggested that it anchors the viral replication complex (VRC) to the membranes. A second highly hydrophobic protein domain (X2) is located immediately upstream of the NTB domain in the RNA1-encoded polyprotein. X2 shares conserved sequence motifs with the comovirus 32-kDa protein, an ER-targeted protein implicated in VRC assembly. In this study, we examined the ability of X2 to associate with intracellular membranes. The X2 protein was fused to the green fluorescent protein and expressed in Nicotiana benthamiana by agroinfiltration. Confocal microscopy and membrane flotation experiments suggested that X2 is targeted to ER membranes. Mutagenesis studies revealed that X2 contains multiple ER-targeting domains, including two C-terminal transmembrane helices and a less-well-defined domain further upstream. To investigate the topology of the protein in the membrane, in vitro glycosylation assays were conducted using X2 derivatives that contained N-glycosylation sites introduced at the N or C termini of the protein. The results led us to propose a topological model for X2 in which the protein traverses the membrane three times, with the N terminus oriented in the lumen and the C terminus exposed to the cytoplasmic face. Taken together, our results indicate that X2 is an ER-targeted polytopic membrane protein and raises the possibility that it acts as a second membrane anchor for the VRC.

scholarly journals ORP5 localizes to ER–lipid droplet contacts and regulates the level of PI(4)P on lipid droplets

2019 ◽  
Vol 219 (1) ◽  
Author(s):  
Ximing Du ◽  
Linkang Zhou ◽  
Yvette Celine Aw ◽  
Hoi Yin Mak ◽  
Yanqing Xu ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Lipid Droplets ◽  
Lipid Synthesis ◽  
Integral Membrane Protein ◽  
Normal Cells ◽  
Bilayer Membranes ◽  
Contact Sites ◽  
Evolutionarily Conserved ◽  
Phosphatidylinositol 4

Lipid droplets (LDs) are evolutionarily conserved organelles that play important roles in cellular metabolism. Each LD is enclosed by a monolayer of phospholipids, distinct from bilayer membranes. During LD biogenesis and growth, this monolayer of lipids expands by acquiring phospholipids from the endoplasmic reticulum (ER) through nonvesicular mechanisms. Here, in a mini-screen, we find that ORP5, an integral membrane protein of the ER, can localize to ER–LD contact sites upon oleate loading. ORP5 interacts with LDs through its ligand-binding domain, and ORP5 deficiency enhances neutral lipid synthesis and increases the size of LDs. Importantly, there is significantly more phosphatidylinositol-4-phosphate (PI(4)P) and less phosphatidylserine (PS) on LDs in ORP5-deficient cells than in normal cells. The increased presence of PI(4)P on LDs in ORP5-deficient cells requires phosphatidylinositol 4-kinase 2-α. Our results thus demonstrate the existence of PI(4)P on LDs and suggest that LD-associated PI(4)P may be primarily used by ORP5 to deliver PS to LDs.

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