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Felix T. Wieland - One of the best experts on this subject based on the ideXlab platform.
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The structures of COPI-coated vesicles reveal alternate Coatomer conformations and interactions
2012Co-Authors: Marco Faini, Felix T. Wieland, Rainer Beck, Britta Brügger, Simone Prinz, Martin Schorb, James D. Riches, Kirsten Bacia, John A. G. BriggsAbstract: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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Induction of cortical endoplasmic reticulum by dimerization of a Coatomer-binding peptide anchored to endoplasmic reticulum membranes
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Grégory Lavieu, Felix T. Wieland, Lelio Orci, Mariella Ravazzola, P. Cosson, Lei Shi, Michael Geiling, James E. RothmanAbstract:Cortical endoplasmic reticulum (cER) is a permanent feature of yeast cells but occurs transiently in most animal cell types. Ist2p is a transmembrane protein that permanently localizes to the cER in yeast. When Ist2 is expressed in mammalian cells, it induces abundant cER containing Ist2. Ist2 cytoplasmic C-terminal peptide is necessary and sufficient to induce cER. This peptide sequence resembles classic coat protein complex I (COPI) Coatomer protein-binding KKXX signals, and indeed the dimerized peptide binds COPI in vitro. Controlled dimerization of this peptide induces cER in cells. RNA interference experiments confirm that Coatomer is required for cER induction in vivo, as are microtubules and the microtubule plus-end binding protein EB1. We suggest that Ist2 dimerization triggers Coatomer binding and clustering of this protein into domains that traffic at the microtubule growing plus-end to generate the cER beneath the plasma membrane. Sequences similar to the Ist2 lysine-rich tail are found in mammalian STIM proteins that reversibly induce the formation of cER under calcium control.
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Differential roles of ArfGAP1, ArfGAP2, and ArfGAP3 in COPI trafficking.
Journal of Cell Biology, 2008Co-Authors: Carolin Weimer, Priska Eckert, Ingeborg Reckmann, Jörg Moelleken, Rainer Beck, Britta Brügger, Felix T. WielandAbstract:The formation of coat protein complex I (COPI)–coated vesicles is regulated by the small guanosine triphosphatase (GTPase) adenosine diphosphate ribosylation factor 1 (Arf1), which in its GTP-bound form recruits Coatomer to the Golgi membrane. Arf GTPase-activating protein (GAP) catalyzed GTP hydrolysis in Arf1 triggers uncoating and is required for uptake of cargo molecules into vesicles. Three mammalian ArfGAPs are involved in COPI vesicle trafficking; however, their individual functions remain obscure. ArfGAP1 binds to membranes depending on their curvature. In this study, we show that ArfGAP2 and ArfGAP3 do not bind directly to membranes but are recruited via interactions with Coatomer. In the presence of Coatomer, ArfGAP2 and ArfGAP3 activities are comparable with or even higher than ArfGAP1 activity. Although previously speculated, our results now demonstrate a function for Coatomer in ArfGAP-catalyzed GTP hydrolysis by Arf1. We suggest that ArfGAP2 and ArfGAP3 are coat protein–dependent ArfGAPs, whereas ArfGAP1 has a more general function.
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a conformational change in the α subunit of Coatomer induced by ligand binding to γ cop revealed by single pair fret
Traffic, 2008Co-Authors: Julian D. Langer, Britta Brügger, Julien Béthune, Christian Roth, Emily H. Stoops, Dirk-peter Herten, Felix T. WielandAbstract:Formation of transport vesicles involves polymerization of cytoplasmic coat proteins (COP). In COPI vesicle biogenesis, the heptameric complex Coatomer is recruited to donor membranes by the interaction of multiple Coatomer subunits with the budding machinery. Specific binding to the trunk domain of γ-COP by the Golgi membrane protein p23 induces a conformational change that causes polymerization of the complex. Using single-pair fluorescence resonance energy transfer, we find that this conformational change takes place in individual Coatomer complexes, independent of each other, and that the conformational rearrangement induced in γ-COP is transmitted within the complex to its α-subunit. We suggest that capture of membrane protein machinery triggers cage formation in the COPI system.
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A Conformational Change in the α‐subunit of Coatomer Induced by Ligand Binding to γ‐COP Revealed by Single‐pair FRET
Traffic (Copenhagen Denmark), 2007Co-Authors: Julian D. Langer, Britta Brügger, Julien Béthune, Christian Roth, Emily H. Stoops, Dirk-peter Herten, Felix T. WielandAbstract:Formation of transport vesicles involves polymerization of cytoplasmic coat proteins (COP). In COPI vesicle biogenesis, the heptameric complex Coatomer is recruited to donor membranes by the interaction of multiple Coatomer subunits with the budding machinery. Specific binding to the trunk domain of γ-COP by the Golgi membrane protein p23 induces a conformational change that causes polymerization of the complex. Using single-pair fluorescence resonance energy transfer, we find that this conformational change takes place in individual Coatomer complexes, independent of each other, and that the conformational rearrangement induced in γ-COP is transmitted within the complex to its α-subunit. We suggest that capture of membrane protein machinery triggers cage formation in the COPI system.
Cordula Harter - One of the best experts on this subject based on the ideXlab platform.
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Oligomerization of peptides analogous to the cytoplasmic domains of Coatomer receptors revealed by mass spectrometry.
Biochemistry, 2000Co-Authors: Thilo A. Fligge, Felix T. Wieland, Constanze Reinhard, Cordula Harter, Michael PrzybylskiAbstract:Members of the p24 family of type I transmembrane proteins are involved in budding of coat protein type I (COPI)-coated vesicles. They serve as coat protein receptors, binding via their cytoplasmic domains to Coatomer, a stable cytosolic protein complex that represents the major coat component of these vesicles. Experimental evidence suggest that p23, a member of the p24 family, binds to Coatomer in an oligomeric state and that this binding triggers polymerization of the coat protein. Toward an understanding of this process at the molecular level, formation of noncovalent complexes and their relative stabilities were analyzed by Fourier transform ion cyclotron resonance mass spectrometry using nanoelectrospray ionization. Specificity and stability of oligomers formed were established to depend on characteristic peptide sequence motifs and were confirmed by mass spectrometric competition experiments with control peptides. Mutations in the peptide sequence caused decreased interaction and destabilization of the noncovalent complexes. The formation and relative stabilities of dimeric and tetrameric complexes were assessed to be formed by cytoplasmic tails of Coatomer receptors. The direct molecular identification provided by mass spectrometry correlates well with biochemical results. Thus, electrospray ionization mass spectrometry proves to be a powerful tool to investigate physiologically relevant peptide complexes.
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Receptor-induced polymerization of Coatomer.
Proceedings of the National Academy of Sciences of the United States of America, 1999Co-Authors: Constanze Reinhard, Britta Brügger, Cordula Harter, M Bremser, K Sohn, J B Helms, Felix T. WielandAbstract:Coatomer, the coat protein complex of COPI vesicles, is involved in the budding of these vesicles, but the underlying mechanism is unknown. Toward a better understanding of this process, the interaction between Coatomer and the cytoplasmic domain of a major transmembrane protein of COPI vesicles, p23, was studied. Interaction of Coatomer with this peptide domain results in a conformational change and polymerization of the complex in vitro. This changed conformation also is observed in vivo, i.e., on the surface of authentic, isolated COPI vesicles. An average of four peptides was found associated with one Coatomer complex after polymerization. Based on these results, we propose a mechanism by which the induced conformational change of Coatomer results in its polymerization, and thus drives formation of the bud on the Golgi membrane during biogenesis of a COPI vesicle.
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A single binding site for dilysine retrieval motifs and p23 within the gamma subunit of Coatomer.
Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Cordula Harter, Felix T. WielandAbstract:Coatomer, the major component of the coat of COPI transport vesicles, binds both to the dilysine motif of resident membrane proteins of the endoplasmic reticulum and to the cytoplasmic domain of p23, a major type I membrane protein of COPI vesicles. Using a photocrosslinking approach, we find that under native conditions a peptide analogous to the cytoplasmic domain of p23 interacts with Coatomer exclusively through its γ subunit and shares its binding site with a KKXX retrieval motif. However, upon dissociation of Coatomer, interaction with various subunits, including an α-, β′-, ɛ-COP subcomplex, of the photoreactive peptide is observed. We suggest that, under physiological conditions, interaction of Coatomer with both endoplasmic reticulum retrieval motifs and the cytoplasmic domain of p23 is mediated by γ-COP.
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Peroxisome biogenesis: involvement of ARF and Coatomer.
The Journal of cell biology, 1998Co-Authors: Michael Passreiter, Felix T. Wieland, Cordula Harter, Markus Anton, Dorothee Lay, Rainer Frank, Karin Gorgas, Wilhelm W. JustAbstract:Peroxisomal membrane protein (Pmp)26p (RnPex11p), a major constituent of induced rat liver peroxisomal membrane, was found to contain a COOH-terminal, cytoplasmically exposed consensus dilysine motif with the potential to bind Coatomer. Biochemical as well as immunocytochemical evidence is presented showing that peroxisomes incubated with preparations of bovine brain or rat liver cytosol recruit ADP-ribosylation factor (ARF) and Coatomer in a strictly guanosine 5'-O-(3-thiotriphosphate)-dependent manner. Consistent with this observation, ldlF cells expressing a temperature-sensitive mutant version of the epsilon-subunit of Coatomer exhibit elongated tubular peroxisomes possibly due to impaired vesiculation at the nonpermissive temperature. Since overexpression of Pex11p in Chinese hamster ovary wild-type cells causes proliferation of peroxisomes, these data suggest that Pex11p plays an important role in peroxisome biogenesis by supporting ARF- and Coatomer-dependent vesiculation of the organelles.
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Reversible dissociation of Coatomer: Functional characterization of a β/δ-coat protein subcomplex
Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Jochen Pavel, Cordula Harter, Felix T. WielandAbstract:COPI-coated vesicles mediate protein transport within the early secretory pathway. Their coat consists of ADP ribosylation factor (ARF1, a small guanosine nucleotide binding protein), and Coatomer, a cytosolic complex composed of seven subunits, α- to ζ-coat proteins (COPs). For coat formation that initiates budding of a vesicle, ARF1 is recruited to the Golgi membrane from the cytosol in its GTP-bound form, and subsequently, Coatomer can bind to the membrane. To identify a minimal structure of Coatomer capable to bind to Golgi membranes in an ARF1-dependent manner, we have established a procedure to dissociate Coatomer under conditions that allow reassociation of the subunits to a complete and functional complex. After dissociation, subunits or subcomplexes can be isolated and may be expected to be functional. Herein we describe isolation of a subcomplex of Coatomer consisting of β- and δ-COPs that is able to bind to Golgi membranes in an ARF1- and GTP-dependent manner.
James E. Rothman - One of the best experts on this subject based on the ideXlab platform.
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Induction of cortical endoplasmic reticulum by dimerization of a Coatomer-binding peptide anchored to endoplasmic reticulum membranes
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Grégory Lavieu, Felix T. Wieland, Lelio Orci, Mariella Ravazzola, P. Cosson, Lei Shi, Michael Geiling, James E. RothmanAbstract:Cortical endoplasmic reticulum (cER) is a permanent feature of yeast cells but occurs transiently in most animal cell types. Ist2p is a transmembrane protein that permanently localizes to the cER in yeast. When Ist2 is expressed in mammalian cells, it induces abundant cER containing Ist2. Ist2 cytoplasmic C-terminal peptide is necessary and sufficient to induce cER. This peptide sequence resembles classic coat protein complex I (COPI) Coatomer protein-binding KKXX signals, and indeed the dimerized peptide binds COPI in vitro. Controlled dimerization of this peptide induces cER in cells. RNA interference experiments confirm that Coatomer is required for cER induction in vivo, as are microtubules and the microtubule plus-end binding protein EB1. We suggest that Ist2 dimerization triggers Coatomer binding and clustering of this protein into domains that traffic at the microtubule growing plus-end to generate the cER beneath the plasma membrane. Sequences similar to the Ist2 lysine-rich tail are found in mammalian STIM proteins that reversibly induce the formation of cER under calcium control.
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Bimodal Interaction of Coatomer with the p24 Family of Putative Cargo Receptors
Science (New York N.Y.), 1996Co-Authors: Klaus Fiedler, Mark Stamnes, Michael Veit, James E. RothmanAbstract:Cytoplasmic domains of members of the p24 family of putative cargo receptors were shown to bind to Coatomer, the coat protein of COPI-coated transport vesicles. Domains that contained dilysine endoplasmic reticulum retrieval signals bound the alpha-, beta'-, and epsilon-COP subunits of Coatomer, whereas other p24 domains bound the beta-, gamma-, and zeta-COP subunits and required a phenylalanine-containing motif. Transit of a CD8-p24 chimera from the endoplasmic reticulum through the Golgi complex was slowed when the phenylalanine motif was mutated, suggesting that this motif may function as an anterograde transport signal. The either-or bimodal binding of Coatomer to p24 tails suggests models for how Coatomer can potentially package retrograde-directed and anterograde-directed cargo into distinct COPI-coated vesicles.
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AN INTEGRAL MEMBRANE COMPONENT OF Coatomer-COATED TRANSPORT VESICLES DEFINES A FAMILY OF PROTEINS INVOLVED IN BUDDING
Proceedings of the National Academy of Sciences of the United States of America, 1995Co-Authors: Mark Stamnes, Mark W. Craighead, Nina Lampen, Scott J. Geromanos, Paul Tempst, James E. RothmanAbstract:Abstract We have isolated a major integral membrane protein from Golgi-derived Coatomer-coated vesicles. This 24-kDa protein, p24, defines a family of integral membrane proteins with homologs present in yeast and humans. In addition to sequence similarity, all p24 family members contain a motif with the characteristic heptad repeats found in coiled coils. When the yeast p24 isoform, yp24A, is knocked out in a strain defective for vesicle fusion, a dramatic reduction in the accumulation of transport vesicles is observed. Together, these results indicate a role for this protein family in the budding of coatamer-coated and other species of coated vesicles.
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Coatomer-rich endoplasmic reticulum.
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: Lelio Orci, James E. Rothman, Mylène Amherdt, Mariella Ravazzola, Alain Perrelet, Randy SchekmanAbstract:Abstract We identify in normal cells the existence of two distinct sites of the transitional endoplasmic reticulum (ER), one housing the Sec23p protein complex (the classical transitional element), the other the Coatomer protein complex (the Coatomer-rich ER). Experimental conditions that reduce transport from the ER to the Golgi complex lead to the overexpression of this newly defined Coatomer-rich ER.
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En bloc incorporation of Coatomer subunits during the assembly of COP- coated vesicles
The Journal of cell biology, 1994Co-Authors: S. Hara-kuge, Osamu Kuge, Lelio Orci, Mylène Amherdt, Mariella Ravazzola, F. T. Wieland, James E. RothmanAbstract:The cDNA encoding epsilon-COP, the 36-kD subunit of Coatomer, was cloned from a bovine liver cDNA library and sequenced. Immunoblotting with an anti-epsilon-COP antibody showed that epsilon-COP exists in COP-coated vesicles as well as in the cytosolic Coatomer. Using the cloned cDNA, recombinant His6- tagged epsilon-COP was overexpressed in cultured Chinese hamster ovary (CHO) cells, from which metabolically radiolabeled Coatomer was purified by taking advantage of the His6 tag. Radiolabeled Coatomer was employed to establish that all the subunits of the Coatomer enter coated vesicles as an intact unit.
Sudip Bajpeyi - One of the best experts on this subject based on the ideXlab platform.
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skeletal muscle perilipin 3 and Coatomer proteins are increased following exercise and are associated with fat oxidation
PLOS ONE, 2014Co-Authors: Jeffrey D Covington, Jose E Galgani, Cedric Moro, Jamie M Lagrange, Zhengyu Zhang, Arild C Rustan, Eric Ravussin, Sudip BajpeyiAbstract:Lipid droplet-associated proteins such as perilipin 3 (PLIN3) and Coatomer GTPase proteins (GBF1, ARF1, Sec23a, and ARFRP1) are expressed in skeletal muscle but little is known so far as to their regulation of lipolysis. We aimed here to explore the effects of lipolytic stimulation in vitro in primary human myotubes as well as in vivo following an acute exercise bout. In vitro lipolytic stimulation by epinephrine (100 μM) or by a lipolytic cocktail (30 μM palmitate, 4 μM forskolin, and 0.5 μM ionomycin, PFI) resulted in increases in PLIN3 protein content. Coatomer GTPases such as GBF1, ARF1, Sec23a, and ARFRP1 also increased in response to lipolytic stimuli. Furthermore, a long duration endurance exercise bout (20 males; age 24.0 ± 4.5 y; BMI 23.6 ± 1.8 kg/m(2)) increased PLIN3 protein in human skeletal muscle (p = 0.03) in proportion to ex vivo palmitate oxidation (r = 0.45, p = 0.04) and whole body in vivo fat oxidation (r = 0.52, p = 0.03). Protein content of ARF1 was increased (p = 0.04) while mRNA expression was increased for several other Coatomers (GBF1, ARF1, and Sec23a, all p<0.05). These data provide novel observational insight into the possible relationships between lipolysis and PLIN3 along with these coatomoer GTPase proteins in human skeletal muscle.
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Skeletal Muscle Perilipin 3 and Coatomer Proteins Are Increased following Exercise and Are Associated with Fat Oxidation
PloS one, 2014Co-Authors: Jeffrey D Covington, Jose E Galgani, Cedric Moro, Jamie M Lagrange, Zhengyu Zhang, Arild C Rustan, Eric Ravussin, Sudip BajpeyiAbstract:Lipid droplet-associated proteins such as perilipin 3 (PLIN3) and Coatomer GTPase proteins (GBF1, ARF1, Sec23a, and ARFRP1) are expressed in skeletal muscle but little is known so far as to their regulation of lipolysis. We aimed here to explore the effects of lipolytic stimulation in vitro in primary human myotubes as well as in vivo following an acute exercise bout. In vitro lipolytic stimulation by epinephrine (100 μM) or by a lipolytic cocktail (30 μM palmitate, 4 μM forskolin, and 0.5 μM ionomycin, PFI) resulted in increases in PLIN3 protein content. Coatomer GTPases such as GBF1, ARF1, Sec23a, and ARFRP1 also increased in response to lipolytic stimuli. Furthermore, a long duration endurance exercise bout (20 males; age 24.0±4.5 y; BMI 23.6±1.8 kg/m2) increased PLIN3 protein in human skeletal muscle (p = 0.03) in proportion to ex vivo palmitate oxidation (r = 0.45, p = 0.04) and whole body in vivo fat oxidation (r = 0.52, p = 0.03). Protein content of ARF1 was increased (p = 0.04) while mRNA expression was increased for several other Coatomers (GBF1, ARF1, and Sec23a, all p
Britta Brügger - One of the best experts on this subject based on the ideXlab platform.
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The structures of COPI-coated vesicles reveal alternate Coatomer conformations and interactions
2012Co-Authors: Marco Faini, Felix T. Wieland, Rainer Beck, Britta Brügger, Simone Prinz, Martin Schorb, James D. Riches, Kirsten Bacia, John A. G. BriggsAbstract: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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Coatomer and dimeric adp ribosylation factor 1 promote distinct steps in membrane scission
Journal of Cell Biology, 2011Co-Authors: Rainer Beck, Britta Brügger, Simone Prinz, Petra Diestelkotterbachert, Simone Rohling, Frank Adolf, Kathrin Hoehner, Sonja Welsch, Paolo Ronchi, John A. G. BriggsAbstract:Formation of coated vesicles requires two striking manipulations of the lipid bilayer. First, membrane curvature is induced to drive bud formation. Second, a scission reaction at the bud neck releases the vesicle. Using a reconstituted system for COPI vesicle formation from purified components, we find that a dimerization-deficient Arf1 mutant, which does not display the ability to modulate membrane curvature in vitro or to drive formation of coated vesicles, is able to recruit Coatomer to allow formation of COPI-coated buds but does not support scission. Chemical cross-linking of this Arf1 mutant restores vesicle release. These experiments show that initial curvature of the bud is defined primarily by Coatomer, whereas the membrane curvature modulating activity of dimeric Arf1 is required for membrane scission.
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Differential roles of ArfGAP1, ArfGAP2, and ArfGAP3 in COPI trafficking.
Journal of Cell Biology, 2008Co-Authors: Carolin Weimer, Priska Eckert, Ingeborg Reckmann, Jörg Moelleken, Rainer Beck, Britta Brügger, Felix T. WielandAbstract:The formation of coat protein complex I (COPI)–coated vesicles is regulated by the small guanosine triphosphatase (GTPase) adenosine diphosphate ribosylation factor 1 (Arf1), which in its GTP-bound form recruits Coatomer to the Golgi membrane. Arf GTPase-activating protein (GAP) catalyzed GTP hydrolysis in Arf1 triggers uncoating and is required for uptake of cargo molecules into vesicles. Three mammalian ArfGAPs are involved in COPI vesicle trafficking; however, their individual functions remain obscure. ArfGAP1 binds to membranes depending on their curvature. In this study, we show that ArfGAP2 and ArfGAP3 do not bind directly to membranes but are recruited via interactions with Coatomer. In the presence of Coatomer, ArfGAP2 and ArfGAP3 activities are comparable with or even higher than ArfGAP1 activity. Although previously speculated, our results now demonstrate a function for Coatomer in ArfGAP-catalyzed GTP hydrolysis by Arf1. We suggest that ArfGAP2 and ArfGAP3 are coat protein–dependent ArfGAPs, whereas ArfGAP1 has a more general function.
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a conformational change in the α subunit of Coatomer induced by ligand binding to γ cop revealed by single pair fret
Traffic, 2008Co-Authors: Julian D. Langer, Britta Brügger, Julien Béthune, Christian Roth, Emily H. Stoops, Dirk-peter Herten, Felix T. WielandAbstract:Formation of transport vesicles involves polymerization of cytoplasmic coat proteins (COP). In COPI vesicle biogenesis, the heptameric complex Coatomer is recruited to donor membranes by the interaction of multiple Coatomer subunits with the budding machinery. Specific binding to the trunk domain of γ-COP by the Golgi membrane protein p23 induces a conformational change that causes polymerization of the complex. Using single-pair fluorescence resonance energy transfer, we find that this conformational change takes place in individual Coatomer complexes, independent of each other, and that the conformational rearrangement induced in γ-COP is transmitted within the complex to its α-subunit. We suggest that capture of membrane protein machinery triggers cage formation in the COPI system.
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A Conformational Change in the α‐subunit of Coatomer Induced by Ligand Binding to γ‐COP Revealed by Single‐pair FRET
Traffic (Copenhagen Denmark), 2007Co-Authors: Julian D. Langer, Britta Brügger, Julien Béthune, Christian Roth, Emily H. Stoops, Dirk-peter Herten, Felix T. WielandAbstract:Formation of transport vesicles involves polymerization of cytoplasmic coat proteins (COP). In COPI vesicle biogenesis, the heptameric complex Coatomer is recruited to donor membranes by the interaction of multiple Coatomer subunits with the budding machinery. Specific binding to the trunk domain of γ-COP by the Golgi membrane protein p23 induces a conformational change that causes polymerization of the complex. Using single-pair fluorescence resonance energy transfer, we find that this conformational change takes place in individual Coatomer complexes, independent of each other, and that the conformational rearrangement induced in γ-COP is transmitted within the complex to its α-subunit. We suggest that capture of membrane protein machinery triggers cage formation in the COPI system.