TY - JOUR
T1 - Sar1p N-terminal helix initiates membrane curvature and completes the fission of a COPII vesicle
AU - Lee, Marcus C.S.
AU - Orci, Lelio
AU - Hamamoto, Susan
AU - Futai, Eugene
AU - Ravazzola, Mariella
AU - Schekman, Randy
N1 - Funding Information:
We thank Crystal Chan for preparing COPII proteins, David Drubin and Georjana Barnes for use of the fluorimeter, Charles Barlowe for Erv46p antisera, Jonathan Goldberg for the Δ23-Sar1p expression plasmid, and Petr Kalab and Karsten Weis for the Ran expression plasmid. We are grateful to Nadine Dupont, A. Widmer, and M. Ebrahim Malek for skillful technical assistance. Special thanks to members of the Schekman lab, especially Liz Miller, for encouragement and critical comments. We also thank Bruno Antonny, Pierre Cosson, Stuart McLaughlin, and Brian Peter for helpful discussions. This work was supported by HHMI (R.S.) and by the Swiss National Science Foundation (L.O.).
PY - 2005/8/26
Y1 - 2005/8/26
N2 - Secretory proteins traffic from the ER to the Golgi via COPII-coated transport vesicles. The five core COPII proteins (Sar1p, Sec23/24p, and Sec13/31p) act in concert to capture cargo proteins and sculpt the ER membrane into vesicles of defined geometry. The molecular details of how the coat proteins deform the lipid bilayer into vesicles are not known. Here we show that the small GTPase Sar1p directly initiates membrane curvature during vesicle biogenesis. Upon GTP binding by Sar1p, membrane insertion of the N-terminal amphipathic α helix deforms synthetic liposomes into narrow tubules. Replacement of bulky hydrophobic residues in the α helix with alanine yields Sar1p mutants that are unable to generate highly curved membranes and are defective in vesicle formation from native ER membranes despite normal recruitment of coat and cargo proteins. Thus, the initiation of vesicle budding by Sar1p couples the generation of membrane curvature with coat-protein assembly and cargo capture.
AB - Secretory proteins traffic from the ER to the Golgi via COPII-coated transport vesicles. The five core COPII proteins (Sar1p, Sec23/24p, and Sec13/31p) act in concert to capture cargo proteins and sculpt the ER membrane into vesicles of defined geometry. The molecular details of how the coat proteins deform the lipid bilayer into vesicles are not known. Here we show that the small GTPase Sar1p directly initiates membrane curvature during vesicle biogenesis. Upon GTP binding by Sar1p, membrane insertion of the N-terminal amphipathic α helix deforms synthetic liposomes into narrow tubules. Replacement of bulky hydrophobic residues in the α helix with alanine yields Sar1p mutants that are unable to generate highly curved membranes and are defective in vesicle formation from native ER membranes despite normal recruitment of coat and cargo proteins. Thus, the initiation of vesicle budding by Sar1p couples the generation of membrane curvature with coat-protein assembly and cargo capture.
UR - http://www.scopus.com/inward/record.url?scp=23944488301&partnerID=8YFLogxK
U2 - 10.1016/j.cell.2005.07.025
DO - 10.1016/j.cell.2005.07.025
M3 - Article
C2 - 16122427
AN - SCOPUS:23944488301
SN - 0092-8674
VL - 122
SP - 605
EP - 617
JO - Cell
JF - Cell
IS - 4
ER -