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A journey through the exocytic pathway
Sophie Béraud-Dufour, William Balch
To cite this version:
Sophie Béraud-Dufour, William Balch. A journey through the exocytic pathway. Journal of Cell Science, Company of Biologists, 2002, 115 (Pt 9), pp.1779-1780. �hal-02266871�
A journey through the
exocytic pathway
Sophie Béraud-Dufour and William Balch*
Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
*Author for correspondence (e-mail: webalch@scripps.edu)
Journal of Cell Science 115, 1779-1780 (2002) © The Company of Biologists Ltd
The poster is composed of three panels, which represent the three major protein families required for the journey of cargo through the exocytic pathway. These families are the ARF and Sar1 family GTPases, which are involved in vesicle formation (left panel), Rab family GTPases, which are involved in vesicle targeting (middle panel) and SNARE family proteins, which participate in vesicle fusion (right panel). The upper half of each panel illustrates the localization of these proteins to their
respective transport steps and/or compartments. In both the upper and lower panels, the mammalian proteins are labeled in black and yeast proteins are labeled in blue. If the mammalian and yeast proteins utilize the same nomenclature, they are highlighted in green. The numbers within the red circles refer to additional effectors (shown in the lower half of each panel) that participate in the indicated transport step.
All eukaryotic cells contain numerous membrane-bound compartments with specialized functions and therefore unique protein compositions. The journey of proteins between these compartments starts by co-translational insertion into the endoplasmic reticulum (ER). Exit from the ER is mediated by COPII vesicles from 100-200 export sites distributed throughout the cell (left panel). COPII coat assembly is regulated by activation of the Sar1 GTPase by the ER-associated guanine nucleotide
exchange factor (GEF) Sec12, which results in the formation of a microtubule-dependent scaffold that initiates cargo selection through tubular intermediates (referred to as transitional elements). Coat assembly and fission is completed by the recruitment of the Sec23/24 guanine nucleotide activating protein (GAP) complex and its regulator, the Sec13/31 complex. Upon fission from the ER, COPII-coated tubules/vesicles lose their coat in response to hydrolysis of GTP. They are subsequently believed to fuse to form the intermediate compartment (IC). Here, proteins exported from the ER can undergo two different fates, either escaped ER resident proteins and misfolded proteins are transported back to the ER via COPI-coated vesicles (left panel), or normal cargo destined for downstream compartments is retained in IC elements that are transported to the pericentriolar region, along microtubule tracks, where they fuse with other IC elements to form
Cell Science at a Glance 1779
(See poster insert)
©Journal of Cell Science 2002 (115, pp.1779-1780)
Syn1,2,3,4 ( Sso1p ,2p ) Late endosome (prevacuole) Lysosome (vacuole) ER Nucleus Syn6 (Tlg1p) Syn10 (Tlg1p) Syn11 Syn16 (Tlg2p) Syn3 Syn5 (Sed5p) Ufe1p ? Smooth ER Syn17 SNARE proteins Syntaxin 6 (Tlg1p) Syntaxin10 Syntaxin11 Syntaxin16 (Tig2p) VTi1 (Vti1p) Snc1p,2p 4 Syntaxin 5 (Sed5p) Membrin (Bos1p) Gos28 (p28) VAMP4 SNAP29 (Spo20p) YKT6 (Ykt6p) Sft1p 3 Syntaxin 5 (Sed5p) Syntaxin 11 SEC22b (Sec22p) YKT6 (Ykt6p) BET1 (Bet1p) p115 (Uso1p) GM130 Giantin p28/GOS28 (Gos1p) 2 Syntaxin 7 (Vam3p) Syntaxin 8 (Vam7p) Vti1 (Vti1p) Cellubrevin (Snc1p,2p) VAMP7,8 (Nyv1p) Endobrevin Vps45 (Vps45p) Vps33 (Vps33p) 6 5 Syntaxin 5 (Sed5p) BET1 (Bet1p) SEC22b (Sec22p) Membrin (Bos1p) 1
Syntaxin 1a,b (Sso1p,2p) VAMP1,2 SNAP25 (Sec9p) Munc18 (Sec1p) NSF (Sec18p) α-SNAP (Sec17p) Syntaxin 1(Sso1p,2p) Syntaxin 2 Syntaxin 3 Syntaxin 4 VAMP5,6 SNAP23 (Sec9p) Cellubrevin (Snc1p,2p) Syntaxin3 VAMP1,2 (Snc1p,2p) Munc18 (Sec1p) SNAP23 (Sec9p) 9 Syntaxin 7 (Vam3p) Syntaxin 8 (Vam7p) Vps33 (Vps33p,11p,18p,16p) Vam3p,7p Nyv1p Vtilp 7 (Melanosome) (Secretory granule) Endosome Cis-Golgi Medial-Golgi Trans-Golgi TGN CGN IC Syn7 (Pep12) Syn8 Syn7 Syn8 8 5 6 Syn1a,b 7 Syn5 (Sed5p) 3 2 1 Syn5 (Sed5p) *LMA1 * Vam7 t-SNARE: Vam3p LMA1 LMA1 Vam7 Vam2/6 Ypt7 Primed vacuoles LMA1 * Ypt7 Reversible tethered vacuoles trans-SNARE priming GTP Ypt7 v-SNARE: Nyv1p Vti1p Ykt6p s-SNARE Isolated vacuoles ATP ADP + Pi LMA1 Sec 17 8 Syntaxin1a SNARE complex RabGTP (R-SNARE) VAMP2 Munc18 GAP α SNAP NSF NSF α SNAP ADP+Pi ATP GDP SNAP25 (Q-SNARE) Munc18 Tethering protein Late endosome (prevacuole) Lysosome (vacuole) ER Cis-Golgi Medial-Golgi Trans-Golgi TGN CGN 2 1 3
Arf and Sar1 proteins ? Arf1 COPI Sar1 COPII
Regulated pathway Constitutive pathway
(Melanosome) (Synaptic vesicle) (Secretory granule) Endosome IC 2 2 Arf1 COPI C Arf1 COPI 2 2 COPI 4 Nucleus 1 3 2 4 p200 Cargo Arf1 GDP COPI Arf1 GTP Arf1 GTP Arf1 GTP Arf GAP or or Cargo Sec23 Sec31 Sec24 Sec13 Sar1 GTP Sec12 Sar1 GDP
COPII coat complex. Many additional components are required for export of specific cargo.
COPII coat consists of Sar1, Sec23/24, Sec13/31 Sec12 [GEF]
Sec23/24 [GAP]
COPI coat consists of α, β, β', γ, ε, δ, ζ subunits p200 (Sec7p, Gea1p, Gea2p) [GEF]
5Arf1 AP3: δ, β3A/3B, µ3A/3B, δ3A/3B Clathrin Late endosome (prevacuole) Lysosome (vacuole) ER HOPS[GEF] RILP [Rab7 effector, dynein-dynactin recruitment factor] Gyp2p,3p,4p,6p,7p [GAPs] Vam2p,6p[R-SNAREs] 5 Rab9 p40 [fusion activator] Tip47 [Rab9 effector, MPR-interacting protein] Rab7 4 2 3 Rab6 Rab8 Rab10 Rab11 (Ypt31p,32p) Rab12 ( R ( R b12 Rab17 Rab1(Ypt1p) Rab6 R b6 Rab12 Rab33b Rab24 Rab1(Ypt1p) Rab30( R b30( Rab33b Rab7 Rab24 5 Rab proteins Rab8 Rab8IP [stress-activated protein] Mss4 Fip2 [Rab8 effector] Rab11 Rab11 FIPI-3 [Rab11 effector] Pp75/Rip11 Eferin Rabphilin 11 TRIP 8b Rab2 may be involved in COPI recruitment Rab33p GM130 Rabaptin 5 Rabex 5 Rab11 Rip11 [Rab11 effector] Eferin [Rab11 effector] RCP [Rab11, Rab4 effector] Rab2 GRASP55-golgin 45 Rab27 [myosin receptor?] Myosin Va [actin motor] Melanophilin [Rab27 effector]
11 Rab3b,c,d Rabphilin RIM1,2 Calmodulin Rabin-3 Rab3-GAP 10 Rab3a Rabaptin5 [Rab5/4-binding protein] Rabphilin [α-actinin-binding protein] RIM1,2 [RIM-BP1-binding protein] Calmodulin [Ca2+sensor] Rabin-3 [GEF] Rab3-GAP [GAP]
9
Rab11a,11b (Ypt31p/32p) Rab11BP TRAPP (TRAPP) [GEF] Eferin Rabphilin11
8
Rab6a,b (Ypt6p)
Rabkinesin6 [MT binding protein] Rab6-KIFL GAPcenA [GAP] Ric1p/Rgp1 p [GEF] (Vps53p,55p,54p) (Yp16p-binding protein) Rab9 Tip47 Rab11 Rabphilin11 7 Rab1a,1b (Ypt1p) RabGDI (Gdi1p) [RabGDP-state chaperone] Mss4 (Dss4p) [empty-state chaperone] p115 (Uso1p) [GM130, giantin binding protein] PRA-1 [Rab receptor ?] TRAPP (TRAPP) [GEF] Gyp1p [GAP] Yip1p-Yif1p all Rab proteins interact with the GDI
GDP GDI p115 Rab1 COP II vesicle GEF GAP ER Golgi-derived vesicle Golgi : CGN GM130 GRASP65 GM 130 GRASP65 GM130 GRASP65 2 3 Rab1 (((Ypt1pY ) Rab1(Ypt1p) Rab2 R b2 Rab6 Rab10 (Ypt7p (Y ( ) Rab6 ? ? Rab6 ? 12Rab2 1 IC Cis-Golgi Medial-Golgi Trans-Golgi TGN CGN 1 * * p115 Rab1 Rab7 (Ypt7p) 6 Sec4p Dss4p Sec3p,8p,5p,6p,10p,15p Sec2p[GEF] Gyp1p,2p,3p,4p[GAP] 12 13 14 15 4 Rab8 Rab11 Rab17 Sec4p 11 Rab27 Rab3b,c,d Rab26 Rab9 Rab7 9 10 14 6 Rab6a (Ypt6p ( ) Rab9 ( R ( R b9 ( R ( Rab11 (Secretory granule) Endosome Rab5 (Ypt51p (Y ( ) Rab15 5 5 5 4 Arf1 γ Synergin γ Clathrin CI-MPR Arf1 GDP Arf1 GTP GEF GAP VHS GGAs (Ggas) GAT EAR
Assembly of GGA-containing coats at the TGN: the GGA proteins are recruited by Arf1–GTP and in turn recruit cargo proteins (MPR), clathrin and accessory proteins (γ synergin).
Assembly of AP1-containing coats at the TGN: the AP1 proteins (γ1/2, β1, µ1A/1B, δ1A/1B/1C) are recruited by Arf1–GTP and in turn recruit clathrin and accessory proteins.
7
Nucleus
Rab1 programming donor membrane
Rab1 programming acceptor membrane
Vacuole homotypic fusion in yeast
Proposed model for vesicles docking and fusion
10Syntaxin 18 (Ufe1p) Sec20p Sec22p Spo20p Sec 18 Va m2/6 9 Syn1 Syn2y Sy2 Syn3y Sy3 Syn4 y S4 y Tlg1p,2p Vam3p Syn11 Syn13 Sed5p Bos1p Syn7, Syn8 Va m2/6
Proteins implicated at indicated transport steps Proteins implicated at indicated transport steps SNARE components and partners involved at indicated steps
10
Regulated pathway Constitutive pathway Regulated pathway Constitutive pathway
GDP Vam7 Arf1 Clathrin C C AP4 GGAs G4 G4 AP1 AP3 AP1 AP3 A Clathrin (Melanosome) (Synaptic vesicle) 13 15 13 (Synaptic vesicle) Cargo protein γ-synergin γ-s γ Arf1 GTP Arf1 COPI COPII GGAs Clathrin 8Rab3a 6Arf1 AP4 Clathrin?
IC assembly: macromolecular complex
COP II vesicle p115 Golgi-derived vesicle GM130 GRASP65 GTP GTP GTP GTP GTP GTP GTP SHD Melanosome Rab27 Myosin Va Slac2a/melanophilin F-Actin GTP GTP GTP β1 µ1δ1 γ
1780
the cis compartment of the Golgi apparatus.
COPI coat assembly on the IC and subsequent Golgi compartments is regulated by the ARF1 GTPase, which promotes the recruitment of the cytosolic COP complex (left panel), containing seven different subunits. ARF1 also participates in the activation of lipid kinase signaling pathways involving PLD that regulate Golgi structure and function. Cargo moves through the Golgi stack in a cis-to-trans direction by a mechanism that is likely to involve directed maturation. In this process, Golgi-resident proteins are sequentially retrieved from more terminal, mature compartments using the COPI retrieval pathway, whereas cargo is collected at the trans face. Here, cargo proteins are sorted to a variety of different destinations. Some will be transported to the plasma membrane using the constitutive pathway, others are sorted via regulated pathways to, for example, secretory granules, secretory lysosomes, such as melanosomes found in melanocytes, or synaptic vesicles that release neurotransmitter at the synapse. In addition, proteins can be transported to endosomes, late endosomes (prevacuoles in yeast) and to lysosomes (vacuoles in yeast). These pathways utilize ARF1 (or, potentially, other ARF isoforms), clathrin and adaptor proteins (AP 1-4) and GGAs to facilitate cargo segregation into distinct vesicle and tubule intermediates that direct cargo along their respective pathways. Vesicle targeting is mediated by Rab
family GTPases (middle panel). The Rab protein family now includes at least 63 isoforms in mammals and 11 in yeast. All Rab proteins are found in the cytosol in the GDP-state complexed with Rab guanine nucleotide dissociation inhibitor (GDI). The Rab-GDI complex delivers each Rab GTPase to a different membrane compartment during formation of transport intermediates, and here they are activated by Rab-specific GEFs. Activated Rabs subsequently recruit a wide variety of effectors that can mediate (1) vesicle motility through linkage to kinesin and myosin motors and/or (2) direct the tethering of transport intermediates to their target membranes. In ER-to-Golgi transport, the Rab1 GTPase found on COPII-derived tubules/vesicles recruits the tether molecule p115, which targets the intermediate to Golgi membranes containing the cognate tether complex GM130-GRASP65.
Vesicle fusion is facilitated by the activity of SNARE proteins (right panel). Fusion requires the formation of trans SNARE complexes that contain at least one R-SNARE, which is usually found on the carrier intermediate (often referred to as the vesicle-associated or v-SNARE, such as VAMP1, which is found on synaptic vesicles involved in neurotransmitter release) and several target-membrane-associated Q-SNAREs (or t-SNAREs, such as syntaxin and SNAP25 proteins, found on the presynaptic membrane). The assembly of trans SNARE complexes requires general factors such as NSF and α -SNAP that function as molecular
chaperones to mediate conformational rearrangements coordinated with the activity of other regulatory proteins and signaling molecules such as Ca2+. Rab
GTPases are likely to play critical role in the ordered assembly of these tethering-fusion complexes. Therefore, the sequential assembly of vesicle coats that direct cargo selection (left panel) and recruitment of the targeting (middle panel) and fusion (right panel) machinery culminates in the formation of a biochemical machine that dictates the specific trafficking of proteins through the exocytic pathway.
Abbreviations used: ARF, ADP-ribosylation factor; CI-MPR, cation-independent mannose 6-phosphate receptor; COPI, coat-binding complex I; COPII, coat-binding complex II; GDI, guanine dissociation inhibitor; GEF; guanine nucleotide exchange factor; GAP, GTPase-activating protein;
GGAs, Golgi-localized, γ-ear-containing
ARF-binding proteins; GM130, Golgi matrix protein 130; GRASP-65, Golgi reassembly stacking protein 65; PI4K, phosphatidylinositol 4-kinase; HOPS, homotypic fusion and vacuole protein sorting; MT, microtubule; NSF, N-ethylmaleimide-sensitive factor; PLD, phospholipase D; Rab11BP, Rab11-binding protein; RCP, Rab coupling protein; RILP, Rab-interacting lysosomal protein; SNAP, soluble N-ethylmaleimide fusion protein attachment protein; v/t-SNARE, vesciular (v)- and target (t)-soluble NSF attachment protein receptors; Vam, vacuolar morphology; Vps, vacuolar protein sorting; TRAPP, transport protein particle.
Journal of Cell Science 115 (9)
Cell Science at a Glance on the Web
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