The genetic basis of a craniofacial disease provides insight into COPII coat assembly.
Proteins trafficking through the secretory pathway must first exit the endoplasmic reticulum (ER) through membrane vesicles created and regulated by the COPII coat protein complex. Cranio-lenticulo-sutural dysplasia (CLSD) was recently shown to be caused by a missense mutation in SEC23A, a gene encoding one of two paralogous COPII coat proteins. We now elucidate the molecular mechanism underlying this disease. In vitro assays reveal that the mutant form of SEC23A poorly recruits the Sec13-Sec31 complex, inhibiting vesicle formation. Surprisingly, this effect is modulated by the Sar1 GTPase paralog used in the reaction, indicating distinct affinities of the two human Sar1 paralogs for the Sec13-Sec31 complex. Patient cells accumulate numerous tubular cargo-containing ER exit sites devoid of observable membrane coat, likely representing an intermediate step in COPII vesicle formation. Our results indicate that the Sar1-Sec23-Sec24 prebudding complex is sufficient to form cargo-containing tubules in vivo, whereas the Sec13-Sec31 complex is required for membrane fission.
Fromme
J Christopher
JC
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
Ravazzola
Mariella
M
Department of Cell Physiology and Metabolism, University of Geneva Medical Center, 1211 Geneva 4, Switzerland.
Hamamoto
Susan
S
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA.
Al-Balwi
Mohammed
M
Department of Pathology and Laboratory Medicine, King Abdulaziz Medical City, Riyadh 11426, Saudi Arabia.
Eyaid
Wafaa
W
Department of Pediatrics, King Fahad Hospital, Riyadh 11426, Saudi Arabia.
Boyadjiev
Simeon A
SA
Section of Genetics, Department of Pediatrics, University of California, Davis, Sacramento, CA 95817, USA.
Cosson
Pierre
P
Department of Cell Physiology and Metabolism, University of Geneva Medical Center, 1211 Geneva 4, Switzerland.
Schekman
Randy
R
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA. Electronic address: schekman@berkeley.edu.
Orci
Lelio
L
Department of Cell Physiology and Metabolism, University of Geneva Medical Center, 1211 Geneva 4, Switzerland. Electronic address: lelio.orci@medecine.unige.ch.
D000595:Amino Acid Sequence; D022181:COP-Coated Vesicles / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D019465:Craniofacial Abnormalities / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D004721:Endoplasmic Reticulum / Q000502:physiology; D005347:Fibroblasts / Q000502:physiology; D006801:Humans; D008561:Membrane Fusion; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D009154:Mutation; D010006:Osteoblasts / Q000502:physiology; D021381:Protein Transport; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
D002352:Carrier Proteins; C507456:SEC13 protein, human; C512739:SEC23A protein, human; C507455:SEC31A protein, human; D033921:Vesicular Transport Proteins; C493083:SAR1A protein, human; D020559:Monomeric GTP-Binding Proteins