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Arora D, Damme DV. Motif-based endomembrane trafficking. PLANT PHYSIOLOGY 2021; 186:221-238. [PMID: 33605419 PMCID: PMC8154067 DOI: 10.1093/plphys/kiab077] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 02/17/2021] [Indexed: 05/08/2023]
Abstract
Endomembrane trafficking, which allows proteins and lipids to flow between the different endomembrane compartments, largely occurs by vesicle-mediated transport. Transmembrane proteins intended for transport are concentrated into a vesicle or carrier by undulation of a donor membrane. This is followed by vesicle scission, uncoating, and finally, fusion at the target membrane. Three major trafficking pathways operate inside eukaryotic cells: anterograde, retrograde, and endocytic. Each pathway involves a unique set of machinery and coat proteins that pack the transmembrane proteins, along with their associated lipids, into specific carriers. Adaptor and coatomer complexes are major facilitators that function in anterograde transport and in endocytosis. These complexes recognize the transmembrane cargoes destined for transport and recruit the coat proteins that help form the carriers. These complexes use either linear motifs or posttranslational modifications to recognize the cargoes, which are then packaged and delivered along the trafficking pathways. In this review, we focus on the different trafficking complexes that share a common evolutionary branch in Arabidopsis (Arabidopsis thaliana), and we discuss up-to-date knowledge about the cargo recognition motifs they use.
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Affiliation(s)
- Deepanksha Arora
- Department of Plant Biotechnology and Bioinformatics, Ghent University, Technologiepark 71, Ghent 9052, Belgium
- VIB Center for Plant Systems Biology, Technologiepark 71, Ghent 9052, Belgium
| | - Daniёl Van Damme
- Department of Plant Biotechnology and Bioinformatics, Ghent University, Technologiepark 71, Ghent 9052, Belgium
- VIB Center for Plant Systems Biology, Technologiepark 71, Ghent 9052, Belgium
- Author for communication:
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2
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Abstract
The coat protein complex I (COPI) allows the precise sorting of lipids and proteins between Golgi cisternae and retrieval from the Golgi to the ER. This essential role maintains the identity of the early secretory pathway and impinges on key cellular processes, such as protein quality control. In this Cell Science at a Glance and accompanying poster, we illustrate the different stages of COPI-coated vesicle formation and revisit decades of research in the context of recent advances in the elucidation of COPI coat structure. By calling attention to an array of questions that have remained unresolved, this review attempts to refocus the perspectives of the field.
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Affiliation(s)
- Eric C Arakel
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, 37073 Göttingen, Germany
| | - Blanche Schwappach
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, 37073 Göttingen, Germany .,Max-Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
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3
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Xu P, Hankins HM, MacDonald C, Erlinger SJ, Frazier MN, Diab NS, Piper RC, Jackson LP, MacGurn JA, Graham TR. COPI mediates recycling of an exocytic SNARE by recognition of a ubiquitin sorting signal. eLife 2017; 6:28342. [PMID: 29058666 PMCID: PMC5663479 DOI: 10.7554/elife.28342] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Accepted: 10/22/2017] [Indexed: 11/17/2022] Open
Abstract
The COPI coat forms transport vesicles from the Golgi complex and plays a poorly defined role in endocytic trafficking. Here we show that COPI binds K63-linked polyubiquitin and this interaction is crucial for trafficking of a ubiquitinated yeast SNARE (Snc1). Snc1 is a v-SNARE that drives fusion of exocytic vesicles with the plasma membrane, and then recycles through the endocytic pathway to the Golgi for reuse in exocytosis. Removal of ubiquitin from Snc1, or deletion of a β'-COP subunit propeller domain that binds K63-linked polyubiquitin, disrupts Snc1 recycling causing aberrant accumulation in internal compartments. Moreover, replacement of the β'-COP propeller domain with unrelated ubiquitin-binding domains restores Snc1 recycling. These results indicate that ubiquitination, a modification well known to target membrane proteins to the lysosome or vacuole for degradation, can also function as recycling signal to sort a SNARE into COPI vesicles in a non-degradative pathway.
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Affiliation(s)
- Peng Xu
- Department of Biological Sciences, Vanderbilt University, Nashville, United States
| | - Hannah M Hankins
- Department of Biological Sciences, Vanderbilt University, Nashville, United States
| | - Chris MacDonald
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, United States
| | - Samuel J Erlinger
- Department of Biological Sciences, Vanderbilt University, Nashville, United States
| | - Meredith N Frazier
- Department of Biological Sciences, Vanderbilt University, Nashville, United States
| | - Nicholas S Diab
- Department of Biological Sciences, Vanderbilt University, Nashville, United States
| | - Robert C Piper
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, United States
| | - Lauren P Jackson
- Department of Biological Sciences, Vanderbilt University, Nashville, United States
| | - Jason A MacGurn
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, United States
| | - Todd R Graham
- Department of Biological Sciences, Vanderbilt University, Nashville, United States
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Shishido F, Uemura S, Kashimura M, Inokuchi JI. Identification of a new B4GalNAcT1 (GM2/GD2/GA2 synthase) isoform, and regulation of enzyme stability and intracellular transport by arginine-based motif. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:2001-2011. [PMID: 28709807 DOI: 10.1016/j.bbamem.2017.07.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Revised: 06/17/2017] [Accepted: 07/10/2017] [Indexed: 11/26/2022]
Abstract
Glycosphingolipids (GSLs) are abundant in plasma membranes of mammalian cells, and their synthesis is strictly regulated in the Golgi apparatus. Disruption of GSL homeostasis is the cause of numerous diseases. Hundreds of molecular species of GSLs exist, and the detailed mechanisms underlying their homeostasis remain unclear. We investigated the physiological significance of isoform production for β1,4-N-acetyl-galactosaminyl transferase 1/B4GALNT1 (B4GN1), an enzyme involved in synthesis of ganglio-series GSLs GM2/GD2/GA2. We discovered a new mRNA variant (termed variant 2) of B4GN1 through EST clone search. A new isoform, M1-B4GN1, which has an NH2-terminal cytoplasmic tail longer than that of previously-known isoform M2-B4GN1, is translated from variant 2. M1-B4GN1 has R-based motif (a retrograde transport signal) in the cytoplasmic tail. M1-B4GN1 is partially localized in the endoplasmic reticulum (ER) depending on the R-based motif, whereas M2-B4GN1 is localized in the Golgi. Stability of M1-B4GN1 is higher than that of M2-B4GN1 because of the R-based motif. M2-B4GN1 forms a homodimer via disulfide bonding. When M1-B4GN1 and M2-B4GN1 were co-expressed in CHO-K1 cells, the two isoforms formed a heterodimer. The M1/M2-B4GN1 heterodimer was more stable than the M2-B4GN1 homodimer, but the heterodimer was not transported from the Golgi to the ER. Our findings indicate that stabilization of M1-B4GN1 homodimer and M1/M2-B4GN1 heterodimer by R-based motif is related to prolongation of Golgi retention, but not to retrograde transport from the Golgi to the ER. Coexistence of several B4GN1 isoforms having distinctive characteristics presumably helps maintain overall enzyme stability and GSL homeostasis.
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Affiliation(s)
- Fumi Shishido
- Division of Glycopathology, Institute of Molecular Biomembrane and Glycobiology, Tohoku Medical and Pharmaceutical University, 4-4-1, Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan
| | - Satoshi Uemura
- Division of Medical Biochemistry, Faculty of Medicine, Tohoku Medical and Pharmaceutical University, 4-4-1, Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan; Division of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
| | - Madoka Kashimura
- Division of Glycopathology, Institute of Molecular Biomembrane and Glycobiology, Tohoku Medical and Pharmaceutical University, 4-4-1, Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan
| | - Jin-Ichi Inokuchi
- Division of Glycopathology, Institute of Molecular Biomembrane and Glycobiology, Tohoku Medical and Pharmaceutical University, 4-4-1, Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan.
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5
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Wang S, Zhai Y, Pang X, Niu T, Ding YH, Dong MQ, Hsu VW, Sun Z, Sun F. Structural characterization of coatomer in its cytosolic state. Protein Cell 2016; 7:586-600. [PMID: 27472951 PMCID: PMC4980336 DOI: 10.1007/s13238-016-0296-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2016] [Accepted: 06/23/2016] [Indexed: 01/27/2023] Open
Abstract
Studies on coat protein I (COPI) have contributed to a basic understanding of how coat proteins generate vesicles to initiate intracellular transport. The core component of the COPI complex is coatomer, which is a multimeric complex that needs to be recruited from the cytosol to membrane in order to function in membrane bending and cargo sorting. Previous structural studies on the clathrin adaptors have found that membrane recruitment induces a large conformational change in promoting their role in cargo sorting. Here, pursuing negative-stain electron microscopy coupled with single-particle analyses, and also performing CXMS (chemical cross-linking coupled with mass spectrometry) for validation, we have reconstructed the structure of coatomer in its soluble form. When compared to the previously elucidated structure of coatomer in its membrane-bound form we do not observe a large conformational change. Thus, the result uncovers a key difference between how COPI versus clathrin coats are regulated by membrane recruitment.
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Affiliation(s)
- Shengliu Wang
- National Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yujia Zhai
- National Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Xiaoyun Pang
- National Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Tongxin Niu
- National Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yue-He Ding
- National Institute of Biological Sciences, Beijing, Beijing, 102206, China
| | - Meng-Qiu Dong
- National Institute of Biological Sciences, Beijing, Beijing, 102206, China
| | - Victor W Hsu
- Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, MA, 02115, USA
| | - Zhe Sun
- National Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.
| | - Fei Sun
- National Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China. .,Center for Biological Imaging, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China. .,University of Chinese Academy of Sciences, Beijing, 100049, China.
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6
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δ-COP contains a helix C-terminal to its longin domain key to COPI dynamics and function. Proc Natl Acad Sci U S A 2016; 113:6916-21. [PMID: 27298352 DOI: 10.1073/pnas.1603544113] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Membrane recruitment of coatomer and formation of coat protein I (COPI)-coated vesicles is crucial to homeostasis in the early secretory pathway. The conformational dynamics of COPI during cargo capture and vesicle formation is incompletely understood. By scanning the length of δ-COP via functional complementation in yeast, we dissect the domains of the δ-COP subunit. We show that the μ-homology domain is dispensable for COPI function in the early secretory pathway, whereas the N-terminal longin domain is essential. We map a previously uncharacterized helix, C-terminal to the longin domain, that is specifically required for the retrieval of HDEL-bearing endoplasmic reticulum-luminal residents. It is positionally analogous to an unstructured linker that becomes helical and membrane-facing in the open form of the AP2 clathrin adaptor complex. Based on the amphipathic nature of the critical helix it may probe the membrane for lipid packing defects or mediate interaction with cargo and thus contribute to stabilizing membrane-associated coatomer.
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7
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Kilisch M, Lytovchenko O, Arakel EC, Bertinetti D, Schwappach B. A dual phosphorylation switch controls 14-3-3-dependent cell surface expression of TASK-1. J Cell Sci 2016; 129:831-42. [PMID: 26743085 PMCID: PMC4760375 DOI: 10.1242/jcs.180182] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Accepted: 12/29/2015] [Indexed: 11/20/2022] Open
Abstract
The transport of the K+ channels TASK-1 and TASK-3 (also known as KCNK3 and KCNK9, respectively) to the cell surface is controlled by the binding of 14-3-3 proteins to a trafficking control region at the extreme C-terminus of the channels. The current model proposes that phosphorylation-dependent binding of 14-3-3 sterically masks a COPI-binding motif. However, the direct effects of phosphorylation on COPI binding and on the binding parameters of 14-3-3 isoforms are still unknown. We find that phosphorylation of the trafficking control region prevents COPI binding even in the absence of 14-3-3, and we present a quantitative analysis of the binding of all human 14-3-3 isoforms to the trafficking control regions of TASK-1 and TASK-3. Surprisingly, the affinities of 14-3-3 proteins for TASK-1 are two orders of magnitude lower than for TASK-3. Furthermore, we find that phosphorylation of a second serine residue in the C-terminus of TASK-1 inhibits 14-3-3 binding. Thus, phosphorylation of the trafficking control region can stimulate or inhibit transport of TASK-1 to the cell surface depending on the target serine residue. Our findings indicate that control of TASK-1 trafficking by COPI, kinases, phosphatases and 14-3-3 proteins is highly dynamic. Summary: Phosphorylation of a previously neglected serine residue in the trafficking control region of TASK-1 interferes with the binding of trafficking machinery and enables complex regulation by physiological stimuli.
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Affiliation(s)
- Markus Kilisch
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, Göttingen 37073, Germany
| | - Olga Lytovchenko
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, Göttingen 37073, Germany
| | - Eric C Arakel
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, Göttingen 37073, Germany
| | | | - Blanche Schwappach
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, Göttingen 37073, Germany Max-Planck Institute for Biophysical Chemistry, Göttingen 37077, Germany
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8
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Papanikou E, Day KJ, Austin J, Glick BS. COPI selectively drives maturation of the early Golgi. eLife 2015; 4. [PMID: 26709839 PMCID: PMC4758959 DOI: 10.7554/elife.13232] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Accepted: 12/27/2015] [Indexed: 12/12/2022] Open
Abstract
COPI coated vesicles carry material between Golgi compartments, but the role of COPI in the secretory pathway has been ambiguous. Previous studies of thermosensitive yeast COPI mutants yielded the surprising conclusion that COPI was dispensable both for the secretion of certain proteins and for Golgi cisternal maturation. To revisit these issues, we optimized the anchor-away method, which allows peripheral membrane proteins such as COPI to be sequestered rapidly by adding rapamycin. Video fluorescence microscopy revealed that COPI inactivation causes an early Golgi protein to remain in place while late Golgi proteins undergo cycles of arrival and departure. These dynamics generate partially functional hybrid Golgi structures that contain both early and late Golgi proteins, explaining how secretion can persist when COPI has been inactivated. Our findings suggest that cisternal maturation involves a COPI-dependent pathway that recycles early Golgi proteins, followed by multiple COPI-independent pathways that recycle late Golgi proteins. DOI:http://dx.doi.org/10.7554/eLife.13232.001 Proteins play many important roles for cells, and these roles often require the proteins to be in particular locations in or around the cells. A set of cell compartments called the Golgi packages certain proteins into bubble-like structures called vesicles to enable the proteins to be used elsewhere in the cell or released to the outside of the cell, in a process called the secretory pathway. The operation of the secretory pathway requires the Golgi compartments to be continually remodeled. Proteins and other materials can be ferried between the compartments of the Golgi by another type of vesicle. These vesicles are coated with a group, or complex, of proteins called COPI, which forms a curved lattice around the vesicles and helps them to capture the materials they will transport. However, it is not clear whether COPI is also involved in remodeling of the Golgi compartments. Papanikou, Day et al. addressed this question using a technique called the “anchor-away method” combined with microscopy to study COPI in yeast cells. The yeast were genetically engineered so that COPI activity was effectively shut down in the presence of a drug called rapamycin. The experiments show that COPI is involved in the early stages of remodeling the Golgi compartments, but not the later stages. This finding supports the emerging view of the Golgi as a self-organizing cellular machine, and it provides a framework for uncovering the engineering principles that underlie the secretory pathway. DOI:http://dx.doi.org/10.7554/eLife.13232.002
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Affiliation(s)
- Effrosyni Papanikou
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Kasey J Day
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Jotham Austin
- Electron Microscopy Core Facility, The University of Chicago, Chicago, United States
| | - Benjamin S Glick
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
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9
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Structure and mechanism of COPI vesicle biogenesis. Curr Opin Cell Biol 2014; 29:67-73. [PMID: 24840894 DOI: 10.1016/j.ceb.2014.04.009] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 04/01/2014] [Accepted: 04/23/2014] [Indexed: 11/22/2022]
Abstract
Distinct trafficking pathways within the secretory and endocytic systems ensure prompt and precise delivery of specific cargo molecules to different cellular compartments via small vesicular (50-150nm) and tubular carriers. The COPI vesicular coat is required for retrograde trafficking from the cis-Golgi back to the ER and within the Golgi stack. Recent structural data have been obtained from X-ray crystallographic studies on COPI coat components alone and on COPI subunits in complex with either cargo motifs or Arf1, and from reconstructions of COPI coated vesicles by electron tomography. These studies provide important molecular information and indicate key differences in COPI coat assembly as compared with clathrin-based and COPII-based coats.
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10
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Chew LH, Setiaputra D, Klionsky DJ, Yip CK. Structural characterization of the Saccharomyces cerevisiae autophagy regulatory complex Atg17-Atg31-Atg29. Autophagy 2013; 9:1467-74. [PMID: 23939028 DOI: 10.4161/auto.25687] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Atg17, in complex with Atg29 and Atg31, constitutes a key module of the Atg1 kinase signaling complex and functions as an important organizer of the phagophore assembly site in the yeast Saccharomyces cerevisiae. We have determined the three-dimensional reconstruction of the full S. cerevisiae Atg17-Atg31-Atg29 complex by single-particle electron microscopy. Our structure shows that Atg17-Atg31-Atg29 is dimeric and adopts a relatively rigid and extended "S-shape" architecture with an end-to-end distance of approximately 345 Å. Subunit mapping analysis indicated that Atg17 mediates dimerization and generates a central rod-like scaffold, while Atg31 and Atg29 form two globular domains that are tethered to the concave sides of the scaffold at the terminal regions. Finally, our observation that Atg17 adopts multiple conformations in the absence of Atg31 and Atg29 suggests that the two smaller components play key roles in defining and maintaining the distinct curvature of the ternary complex.
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Affiliation(s)
- Leon H Chew
- Department of Biochemistry and Molecular Biology; The University of British Columbia; Vancouver, British Columbia Canada
| | - Dheva Setiaputra
- Department of Biochemistry and Molecular Biology; The University of British Columbia; Vancouver, British Columbia Canada
| | | | - Calvin K Yip
- Department of Biochemistry and Molecular Biology; The University of British Columbia; Vancouver, British Columbia Canada
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11
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Abstract
The secretory pathway is responsible for the synthesis, folding, and delivery of a diverse array of cellular proteins. Secretory protein synthesis begins in the endoplasmic reticulum (ER), which is charged with the tasks of correctly integrating nascent proteins and ensuring correct post-translational modification and folding. Once ready for forward traffic, proteins are captured into ER-derived transport vesicles that form through the action of the COPII coat. COPII-coated vesicles are delivered to the early Golgi via distinct tethering and fusion machineries. Escaped ER residents and other cycling transport machinery components are returned to the ER via COPI-coated vesicles, which undergo similar tethering and fusion reactions. Ultimately, organelle structure, function, and cell homeostasis are maintained by modulating protein and lipid flux through the early secretory pathway. In the last decade, structural and mechanistic studies have added greatly to the strong foundation of yeast genetics on which this field was built. Here we discuss the key players that mediate secretory protein biogenesis and trafficking, highlighting recent advances that have deepened our understanding of the complexity of this conserved and essential process.
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12
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Vesicle coats: structure, function, and general principles of assembly. Trends Cell Biol 2013; 23:279-88. [DOI: 10.1016/j.tcb.2013.01.005] [Citation(s) in RCA: 139] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Revised: 12/27/2012] [Accepted: 01/10/2013] [Indexed: 01/03/2023]
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13
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Jackson LP, Lewis M, Kent HM, Edeling MA, Evans PR, Duden R, Owen DJ. Molecular basis for recognition of dilysine trafficking motifs by COPI. Dev Cell 2012. [PMID: 23177648 PMCID: PMC3521961 DOI: 10.1016/j.devcel.2012.10.017] [Citation(s) in RCA: 99] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
COPI mediates retrograde trafficking from the Golgi to the endoplasmic reticulum (ER) and within the Golgi stack, sorting transmembrane proteins bearing C-terminal KKxx or KxKxx motifs. The structure of KxKxx motifs bound to the N-terminal WD-repeat domain of β'-COP identifies electrostatic contacts between the motif and complementary patches at the center of the β'-COP propeller. An absolute requirement of a two-residue spacing between the terminal carboxylate group and first lysine residue results from interactions of carbonyl groups in the motif backbone with basic side chains of β'-COP. Similar interactions are proposed to mediate binding of KKxx motifs by the homologous α-COP domain. Mutation of key interacting residues in either domain or in their cognate motifs abolishes in vitro binding and results in mistrafficking of dilysine-containing cargo in yeast without compromising cell viability. Flexibility between β'-COP WD-repeat domains and the location of cargo binding have implications for COPI coat assembly.
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Affiliation(s)
- Lauren P Jackson
- Cambridge Institute for Medical Research, Department of Clinical Biochemistry, University of Cambridge, Hills Road, Cambridge CB2 0XY, UK.
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14
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Jackson LP, Kümmel D, Reinisch KM, Owen DJ. Structures and mechanisms of vesicle coat components and multisubunit tethering complexes. Curr Opin Cell Biol 2012; 24:475-83. [PMID: 22728063 PMCID: PMC3425711 DOI: 10.1016/j.ceb.2012.05.013] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Accepted: 05/23/2012] [Indexed: 11/17/2022]
Abstract
Eukaryotic cells face a logistical challenge in ensuring prompt and precise delivery of vesicular cargo to specific organelles within the cell. Coat protein complexes select cargo and initiate vesicle formation, while multisubunit tethering complexes participate in the delivery of vesicles to target membranes. Understanding these macromolecular assemblies has greatly benefited from their structural characterization. Recent structural data highlight principles in coat recruitment and uncoating in both the endocytic and retrograde pathways, and studies on the architecture of tethering complexes provide a framework for how they might link vesicles to the respective acceptor compartments and the fusion machinery.
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Affiliation(s)
- Lauren P Jackson
- Cambridge Institute for Medical Research, Department of Clinical Biochemistry, University of Cambridge, Cambridge CB2 0XY, UK.
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15
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Faini M, Prinz S, Beck R, Schorb M, Riches JD, Bacia K, Brügger B, Wieland FT, Briggs JAG. The structures of COPI-coated vesicles reveal alternate coatomer conformations and interactions. Science 2012; 336:1451-4. [PMID: 22628556 DOI: 10.1126/science.1221443] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Transport between compartments of eukaryotic cells is mediated by coated vesicles. The archetypal protein coats COPI, COPII, and clathrin are conserved from yeast to human. Structural studies of COPII and clathrin coats assembled in vitro without membranes suggest that coat components assemble regular cages with the same set of interactions between components. Detailed three-dimensional structures of coated membrane vesicles have not been obtained. Here, we solved the structures of individual COPI-coated membrane vesicles by cryoelectron tomography and subtomogram averaging of in vitro reconstituted budding reactions. The coat protein complex, coatomer, was observed to adopt alternative conformations to change the number of other coatomers with which it interacts and to form vesicles with variable sizes and shapes. This represents a fundamentally different basis for vesicle coat assembly.
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Affiliation(s)
- Marco Faini
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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16
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Abstract
Coatomer protein I (COPI) is well known as the protein coat surrounding vesicles involved in returning endoplasmic reticulum (ER)-resident proteins to the ER. COPI coats are also found in vesicles involved in other trafficking processes including endocytosis, autophagy and anterograde transport in the secretory pathway. In view of the diverse functions of COPI proteins, it is expected that they will affect virus replication, and many reports of such COPI involvement have now appeared. The experimental approaches most often employ specific siRNA to deplete COPI subunits or brefeldin A to block COPI activation. Here we briefly describe the results obtained with viruses in which COPI is found to have a role in replication. The results demonstrate that COPI affects viruses quite differently with effects observed in processes such as entry, RNA replication, and intracellular transport of viral proteins.
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Affiliation(s)
- Jennifer A Thompson
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia Health System, Charlottesville, Virginia 22908
| | - Jay C Brown
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia Health System, Charlottesville, Virginia 22908
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