scholarly journals The Secretory Apparatus of an Ancient Eukaryote: Protein Sorting to Separate Export Pathways Occurs Before Formation of Transient Golgi-like Compartments

2003 ◽  
Vol 14 (4) ◽  
pp. 1433-1447 ◽  
Author(s):  
Matthias Marti ◽  
Yajie Li ◽  
Elisabeth M. Schraner ◽  
Peter Wild ◽  
Peter Köhler ◽  
...  
Keyword(s):  
Secretory Pathway ◽  
Protein Sorting ◽  
Protozoan Parasite ◽  
Retrograde Transport ◽  
Surface Proteins ◽  
Cyst Form ◽  
Early Secretory Pathway ◽  
Vertebrate Hosts ◽  
Er Export ◽  
Secretory Apparatus

Transmission of the protozoan parasite Giardia intestinalis to vertebrate hosts presupposes the encapsulation of trophozoites into an environmentally resistant and infectious cyst form. We have previously shown that cyst wall proteins were faithfully sorted to large encystation-specific vesicles (ESVs), despite the absence of a recognizable Golgi apparatus. Here, we demonstrate that sorting to a second constitutively active pathway transporting variant-specific surface proteins (VSPs) to the surface depended on the cytoplasmic VSP tail. Moreover, pulsed endoplasmic reticulum (ER) export of chimeric reporters containing functional signals for both pathways showed that protein sorting was done at or very soon after export from the ER. Correspondingly, we found that a limited number of novel transitional ER-like structures together with small transport intermediates were generated during encystation. Colocalization of transitional ER regions and early ESVs with coat protein (COP) II and of maturing ESVs with COPI and clathrin strongly suggested that ESVs form by fusion of ER-derived vesicles and subsequently undergo maturation by retrograde transport. Together, the data supported the hypothesis that in Giardia, a primordial secretory apparatus is in operation by which proteins are sorted in the early secretory pathway, and the developmentally induced ESVs carry out at least some Golgi functions.

scholarly journals Molecular basis for KDEL-mediated retrieval of escaped ER-resident proteins – SWEET talking the COPs

2020 ◽  
Vol 133 (19) ◽  
pp. jcs250100
Author(s):  
Simon Newstead ◽  
Francis Barr
Keyword(s):  
Secretory Pathway ◽  
Signal Sequence ◽  
Structural Similarity ◽  
Retrograde Transport ◽  
Coated Vesicles ◽  
Early Secretory Pathway ◽  
Cargo Proteins ◽  
Protein Localisation ◽  
And Function ◽  
Trafficking Receptor

ABSTRACTProtein localisation in the cell is controlled through the function of trafficking receptors, which recognise specific signal sequences and direct cargo proteins to different locations. The KDEL receptor (KDELR) was one of the first intracellular trafficking receptors identified and plays an essential role in maintaining the integrity of the early secretory pathway. The receptor recognises variants of a canonical C-terminal Lys-Asp-Glu-Leu (KDEL) signal sequence on ER-resident proteins when these escape to the Golgi, and targets these proteins to COPI- coated vesicles for retrograde transport back to the ER. The empty receptor is then recycled from the ER back to the Golgi by COPII-coated vesicles. Crystal structures of the KDELR show that it is structurally related to the PQ-loop family of transporters that are found in both pro- and eukaryotes, and shuttle sugars, amino acids and vitamins across cellular membranes. Furthermore, analogous to PQ-loop transporters, the KDELR undergoes a pH-dependent and ligand-regulated conformational cycle. Here, we propose that the striking structural similarity between the KDELR and PQ-loop transporters reveals a connection between transport and trafficking in the cell, with important implications for understanding trafficking receptor evolution and function.

scholarly journals Involvement of Specific COPI Subunits in Protein Sorting from the Late Endosome to the Vacuole in Yeast

2006 ◽  
Vol 27 (2) ◽  
pp. 526-540 ◽  
Author(s):  
Galina Gabriely ◽  
Rachel Kama ◽  
Jeffrey E. Gerst
Keyword(s):  
Mammalian Cells ◽  
Secretory Pathway ◽  
Protein Sorting ◽  
Multivesicular Body ◽  
Carboxypeptidase Y ◽  
Direct Role ◽  
Vacuolar Protein Sorting ◽  
Early Secretory Pathway ◽  
Physical Interactions ◽  
Vacuolar Protein

ABSTRACT Although COPI function on the early secretory pathway in eukaryotes is well established, earlier studies also proposed a nonconventional role for this coat complex in endocytosis in mammalian cells. Here we present results that suggest an involvement for specific COPI subunits in the late steps of endosomal protein sorting in Saccharomyces cerevisiae. First, we found that carboxypeptidase Y (CPY) was partially missorted to the cell surface in certain mutants of the COPIB subcomplex (COPIb; Sec27, Sec28, and possibly Sec33), which indicates an impairment in endosomal transport. Second, integral membrane proteins destined for the vacuolar lumen (i.e., carboxypeptidase S [CPS1]; Fur4, Ste2, and Ste3) accumulated at an aberrant late endosomal compartment in these mutants. The observed phenotypes for COPIb mutants resemble those of class E vacuolar protein sorting (vps) mutants that are impaired in multivesicular body (MVB) protein sorting and biogenesis. Third, we observed physical interactions and colocalization between COPIb subunits and an MVB-associated protein, Vps27. Together, our findings suggest that certain COPI subunits could have a direct role in vacuolar protein sorting to the MVB compartment.

Lectins and protein traffic early in the secretory pathway

2002 ◽  
Vol 69 ◽  
pp. 73-82 ◽  
Author(s):  
Hans-Peter Hauri ◽  
Oliver Nufer ◽  
Lionel Breuza ◽  
Houchaima Ben Tekaya ◽  
Lu Liang
Keyword(s):  
Membrane Protein ◽  
Secretory Pathway ◽  
Integral Membrane Protein ◽  
Type I ◽  
Coat Proteins ◽  
Protein Traffic ◽  
Early Secretory Pathway ◽  
Er Export ◽  
Different Characteristics ◽  
Related Proteins

Lectins of the early secretory pathway are involved in selective transport of newly synthesized glycoproteins from the endoplasmic reticulum (ER) to the ER–Golgi intermediate compartment (ERGIC). The most prominent cycling lectin is the mannose-binding type I membrane protein ERGIC-53 (ERGIC protein of 53 kDa), a marker for the ERGIC, which functions as a cargo receptor to facilitate export of an increasing number of glycoproteins with different characteristics from the ER. Two ERGIC-53-related proteins, VIP36 (vesicular integral membrane protein 36) and a novel ERGIC-53-like protein, ERGL, are also found in the early secretory pathway. ERGL may act as a regulator of ERGIC-53. Studies of ERGIC-53 continue to provide new insights into the organization and dynamics of the early secretory pathway. Analysis of the cycling of ERGIC-53 uncovered a complex interplay of trafficking signals and revealed novel cytoplasmic ER-export motifs that interact with COP-II coat proteins. These motifs are common to type I and polytopic membrane proteins including presenilin 1 and presenilin 2. The results support the notion that protein export from the ER is selective.

scholarly journals Localization and Recycling of gp27 (hp24γ3): Complex Formation with Other p24 Family Members

1999 ◽  
Vol 10 (6) ◽  
pp. 1939-1955 ◽  
Author(s):  
Joachim Füllekrug ◽  
Tatsuo Suganuma ◽  
Bor Luen Tang ◽  
Wanjing Hong ◽  
Brian Storrie ◽  
...  
Keyword(s):  
Steady State ◽  
Complex Formation ◽  
Secretory Pathway ◽  
Dynamic Equilibrium ◽  
Brefeldin A ◽  
Temperature Treatment ◽  
Dominant Negative ◽  
Dominant Negative Mutant ◽  
Early Secretory Pathway ◽  
Er Export

We report here the characterization of gp27 (hp24γ3), a glycoprotein of the p24 family of small and abundant transmembrane proteins of the secretory pathway. Immunoelectron and confocal scanning microscopy show that at steady state, gp27 localizes to thecis side of the Golgi apparatus. In addition, some gp27 was detected in COPI- and COPII-coated structures throughout the cytoplasm. This indicated cycling that was confirmed in three ways. First, 15°C temperature treatment resulted in accumulation of gp27 in pre-Golgi structures colocalizing with anterograde cargo. Second, treatment with brefeldin A caused gp27 to relocate into peripheral structures positive for both KDEL receptor and COPII. Third, microinjection of a dominant negative mutant of Sar1p trapped gp27 in the endoplasmic reticulum (ER) by blocking ER export. Together, this shows that gp27 cycles extensively in the early secretory pathway. Immunoprecipitation and coexpression studies further revealed that a significant fraction of gp27 existed in a hetero-oligomeric complex. Three members of the p24 family, GMP25 (hp24α2), p24 (hp24β1), and p23 (hp24δ1), coprecipitated in what appeared to be stochiometric amounts. This heterocomplex was specific. Immunoprecipitation of p26 (hp24γ4) failed to coprecipitate GMP25, p24, or p23. Also, very little p26 was found coprecipitating with gp27. A functional requirement for complex formation was suggested at the level of ER export. Transiently expressed gp27 failed to leave the ER unless other p24 family proteins were coexpressed. Comparison of attached oligosaccharides showed that gp27 and GMP25 recycled differentially. Only a very minor portion of GMP25 displayed complex oligosaccharides. In contrast, all of gp27 showed modifications by medial and trans enzymes at steady state. We conclude from these data that a portion of gp27 exists as hetero-oligomeric complexes with GMP25, p24, and p23 and that these complexes are in dynamic equilibrium with individual p24 proteins to allow for differential recycling and distributions.

The trials and tubule-ations of Rab6 involvement in Golgi-to-ER retrograde transport

2014 ◽  
Vol 42 (5) ◽  
pp. 1453-1459 ◽  
Author(s):  
Linda F. Heffernan ◽  
Jeremy C. Simpson
Keyword(s):  
Secretory Pathway ◽  
Size Composition ◽  
Retrograde Transport ◽  
Retrograde Flow ◽  
Transport Pathway ◽  
Membrane Flow ◽  
Transport Pathways ◽  
Complex Needs ◽  
Early Secretory Pathway ◽  
Regulatory Machinery

In the early secretory pathway, membrane flow in the anterograde direction from the endoplasmic reticulum (ER) to the Golgi complex needs to be tightly co-ordinated with retrograde flow to maintain the size, composition and functionality of these two organelles. At least two mechanisms of transport move material in the retrograde direction: one regulated by the cytoplasmic coatomer protein I complex (COPI), and a second COPI-independent pathway utilizing the small GTP-binding protein Rab6. Although the COPI-independent pathway was discovered 15 years ago, it remains relatively poorly characterized, with only a handful of machinery molecules associated with its operation. One feature that makes this pathway somewhat unusual, and potentially difficult to study, is that the transport carriers predominantly seem to be tubular rather than vesicular in nature. This suggests that the regulatory machinery is likely to be different from that associated with vesicular transport pathways controlled by conventional coat complexes. In the present mini-review, we have highlighted the key experiments that have characterized this transport pathway so far and also have discussed the challenges that lie ahead with respect to its further characterization.

scholarly journals Diacylglycerol Is Required for the Formation of COPI Vesicles in the Golgi-to-ER Transport Pathway

2007 ◽  
Vol 18 (9) ◽  
pp. 3250-3263 ◽  
Author(s):  
Inés Fernández-Ulibarri ◽  
Montserrat Vilella ◽  
Francisco Lázaro-Diéguez ◽  
Elisabet Sarri ◽  
Susana E. Martínez ◽  
...  
Keyword(s):  
Secretory Pathway ◽  
Electron Tomography ◽  
Critical Role ◽  
Retrograde Transport ◽  
Transport Pathway ◽  
Surface Transport ◽  
Early Secretory Pathway ◽  
Membrane Fission ◽  
Functional Relevance ◽  
Golgi Network

Diacylglycerol is necessary for trans-Golgi network (TGN) to cell surface transport, but its functional relevance in the early secretory pathway is unclear. Although depletion of diacylglycerol did not affect ER-to-Golgi transport, it led to a redistribution of the KDEL receptor to the Golgi, indicating that Golgi-to-ER transport was perturbed. Electron microscopy revealed an accumulation of COPI-coated membrane profiles close to the Golgi cisternae. Electron tomography showed that the majority of these membrane profiles originate from coated buds, indicating a block in membrane fission. Under these conditions the Golgi-associated pool of ARFGAP1 was reduced, but there was no effect on the binding of coatomer or the membrane fission protein CtBP3/BARS to the Golgi. The addition of 1,2-dioctanoyl-sn-glycerol or the diacylglycerol analogue phorbol 12,13-dibutyrate reversed the effects of endogenous diacylglycerol depletion. Our findings implicate diacylglycerol in the retrograde transport of proteins from Golgi to the ER and suggest that it plays a critical role at a late stage of COPI vesicle formation.

Protein Sorting Receptors in the Early Secretory Pathway

2010 ◽  
Vol 79 (1) ◽  
pp. 777-802 ◽  
Author(s):  
Julia Dancourt ◽  
Charles Barlowe
Keyword(s):  
Secretory Pathway ◽  
Protein Sorting ◽  
Early Secretory Pathway

scholarly journals The TRAPP complex mediates secretion arrest induced by stress granule assembly

2019 ◽  
Author(s):  
Francesca Zappa ◽  
Cathal Wilson ◽  
Giuseppe Di Tullio ◽  
Michele Santoro ◽  
Piero Pucci ◽  
...  
Keyword(s):  
Membrane Trafficking ◽  
Secretory Pathway ◽  
Acute Stress ◽  
Stress Exposure ◽  
Proliferating Cells ◽  
Early Secretory Pathway ◽  
Er Exit Sites ◽  
Protein Particle ◽  
Mediate Cell ◽  
Er Export

The TRAnsport-Protein-Particle (TRAPP) complex controls multiple membrane trafficking steps and is thus strategically positioned to mediate cell adaptation to diverse environmental conditions, including acute stress. We have identified TRAPP as a key component of a branch of the integrated stress response that impinges on the early secretory pathway. TRAPP associates with and drives the recruitment of the COPII coat to stress granules (SGs) leading to vesiculation of the Golgi complex and an arrest of ER export. Interestingly, the relocation of TRAPP and COPII to SGs only occurs in actively proliferating cells and is CDK1/2-dependent. We show that CDK1/2 activity controls the COPII cycle at ER exit sites (ERES) and that its inhibition prevents TRAPP/COPII relocation to SGs by stabilizing them at the ERES. Importantly, TRAPP is not just a passive constituent of SGs but controls their maturation since SGs that assemble in TRAPP-depleted cells are smaller and are no longer able to recruit RACK1 and Raptor, rendering the cells more prone to undergo apoptosis upon stress exposure.

scholarly journals The transmembrane protein p23 contributes to the organization of the Golgi apparatus

2000 ◽  
Vol 113 (6) ◽  
pp. 1043-1057 ◽  
Author(s):  
M. Rojo ◽  
G. Emery ◽  
V. Marjomaki ◽  
A.W. McDowall ◽  
R.G. Parton ◽  
...  
Keyword(s):  
Golgi Apparatus ◽  
Secretory Pathway ◽  
Transmembrane Protein ◽  
Ectopic Expression ◽  
Retrograde Transport ◽  
Early Secretory Pathway ◽  
Golgi Membranes ◽  
Constant Diameter ◽  
Golgi Network

In previous studies we have shown that p23, a member of the p24-family of small transmembrane proteins, is highly abundant in membranes of the cis-Golgi network (CGN), and is involved in sorting/trafficking in the early secretory pathway. In the present study, we have further investigated the role of p23 after ectopic expression. We found that ectopically expressed p23 folded and oligomerized properly, even after overexpression. However, in contrast to endogenous p23, exogenous p23 molecules did not localize to the CGN, but induced a significant expansion of characteristic smooth ER membranes, where they accumulated in high amounts. This ER-derived, p23-rich subdomain displayed a highly regular morphology, consisting of tubules and/or cisternae of constant diameter, which were reminiscent of the CGN membranes containing p23 in control cells. The expression of exogenous p23 also led to the specific relocalization of endogenous p23, but not of other proteins, to these specialized ER-derived membranes. Relocalization of p23 modified the ultrastructure of the CGN and Golgi membranes, but did not affect anterograde and retrograde transport reactions to any significant extent. We conclude (i) that p23 has a morphogenic activity that contributes to the morphology of CGN-membranes; and (ii) that the presence of p23 in the CGN is necessary for the proper organization of the Golgi apparatus.

scholarly journals A Role for Lipids in Protein Sorting?

2021 ◽  
Vol 75 (12) ◽  
pp. 1026-1030
Author(s):  
Auxiliadora Aguilera-Romero ◽  
Manuel Muñiz
Keyword(s):  
Secretory Pathway ◽  
Membrane Lipids ◽  
Protein Sorting ◽  
Eukaryotic Cell ◽  
Surface Proteins ◽  
Protein Diversity ◽  
Membrane Compartments ◽  
Open Discussion ◽  
Interdisciplinary Study

Lipid and protein diversity provides structural and functional identity to the membrane compartments that define the eukaryotic cell. This compositional heterogeneity is maintained by the secretory pathway, which feeds newly synthesized proteins and lipids to the endomembrane systems. The precise sorting of lipids and proteins through the pathway guarantees the achievement of their correct delivery. Although proteins have been shown to be key for sorting mechanisms, whether and how lipids contribute to this process is still an open discussion. Our laboratory, in collaboration with other groups, has recently addressed the long-postulated role of membrane lipids in protein sorting in the secretory pathway, by investigating in yeast how a special class of lipid-linked cell surface proteins are differentially exported from the endoplasmic reticulum. Here we comment on this interdisciplinary study that highlights the role of lipid diversity and the importance of protein-lipid interactions in sorting processes at the cell membrane.

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