COPII proteins play a critical role in the early secretory pathway by transporting protein and lipid cargo out of the endoplasmic reticulum (ER). The COPII proteins consist of Sar1 (a GTPase), Sec23/24 (cargo selection and GAP activity), and Sec13/31 (promotes coat assembly). Together, these form a coat that recruits and concentrates cargo and gradually deforms the ER membrane into a vesicle. Recently, it was found that Sec13/31 self-assembles into a unique cuboctahedron cage-like structure. These structures were solved with cryo-electron microscopy (cryoEM) and single particle reconstruction and yielded insights into some of the mechanisms by which COPII coated vesicles are assembled. These initial studies were bolstered with a new structure of a COPII coat formed from the self-assembly of Sec13/31 with Sec23/24. Together, these two structures form a foundation for dissecting the mechanisms by which the COPII proteins perform their functions in the cell. The current proposal seeks to address questions about COPII structure and assembly through four specific aims.
Aim 1 proposes to determine the structures of individual COPII coats and COPII coated vesicles. These structures will shed light on the ways that cargo interacts with Sec23/24 and Sec23/24 interacts with Sec13/31, and thus contribute to a picture of the mechanisms by which cargo directs the assembly of vesicles of the proper size.
In aim 2, it is proposed to determine the structure of the COPII coat in complex with Sar1, and these studies will reveal at a molecular level how Sar1 is involved in initiating the formation of the COPII coat. The molecular mechanisms of tethering are explored in aim 3, where it is proposed to determine the structure of the COPII coat in complex with the TRAPPI tether protein Bet3. Finally, aim 4 proposes to develop assays for poisoning COPII cage assembly at various intermediate stages and to determine the structures of the intermediates. Together, these studies will drive the vesicle transport field by furthering our understanding of COPII structures and how they are assembled in the cell. This, in turn, will aid in the understanding of the role COPII proteins play in diseases like chylomicron retention disease and cranio-lenticulo-sutural dysplasia, which result from mutations in Sar1 and Sec23/24 respectively, and diseases that manifest as transport defects such as cystic fibrosis.

Public Health Relevance

The COPII proteins are involved in the secretory pathway, which is a critical and fundamental pathway in eukaryotes such as humans. Two diseases, chylomicron retention disease and cranio-lenticulo sutural dysplasia, are associated with mutations in COPII proteins, and a host of diseases including cystic fibrosis result from mutations that cause the proteins to be retained in the ER. Understanding of the mechanisms by which cargo proteins interact with the COPII coat and how COPII coat assembles will help us understand the role COPII plays in these diseases and may help in identifying novel targets for therapeutics.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
1R01GM086892-01A2
Application #
7987056
Study Section
Macromolecular Structure and Function C Study Section (MSFC)
Program Officer
Flicker, Paula F
Project Start
2010-08-01
Project End
2015-07-31
Budget Start
2010-08-01
Budget End
2011-07-31
Support Year
1
Fiscal Year
2010
Total Cost
$241,681
Indirect Cost
Name
Florida State University
Department
Chemistry
Type
Schools of Arts and Sciences
DUNS #
790877419
City
Tallahassee
State
FL
Country
United States
Zip Code
32306
Slosarek, Erin L; Schuh, Amber L; Pustova, Iryna et al. (2018) Pathogenic TFG Mutations Underlying Hereditary Spastic Paraplegia Impair Secretory Protein Trafficking and Axon Fasciculation. Cell Rep 24:2248-2260
Paraan, Mohammadreza; Bhattacharya, Nilakshee; Uversky, Vladimir N et al. (2018) Flexibility of the Sec13/31 cage is influenced by the Sec31 C-terminal disordered domain. J Struct Biol 204:250-260
Xie, Qing; Spear, John M; Noble, Alex J et al. (2017) The 2.8 Å Electron Microscopy Structure of Adeno-Associated Virus-DJ Bound by a Heparinoid Pentasaccharide. Mol Ther Methods Clin Dev 5:1-12
Lowry, Troy W; Hariri, Hanaa; Prommapan, Plengchart et al. (2016) Quantification of Protein-Induced Membrane Remodeling Kinetics In Vitro with Lipid Multilayer Gratings. Small 12:506-15
Spear, John M; Noble, Alex J; Xie, Qing et al. (2015) The influence of frame alignment with dose compensation on the quality of single particle reconstructions. J Struct Biol 192:196-203
Noble, Alex J; Stagg, Scott M (2015) Automated batch fiducial-less tilt-series alignment in Appion using Protomo. J Struct Biol 192:270-8
Gianfelice, Antonella; Le, Phuong H B; Rigano, Luciano A et al. (2015) Host endoplasmic reticulum COPII proteins control cell-to-cell spread of the bacterial pathogen Listeria monocytogenes. Cell Microbiol 17:876-92
Spear, John M; Koborssy, Dolly Al; Schwartz, Austin B et al. (2015) Kv1.3 contains an alternative C-terminal ER exit motif and is recruited into COPII vesicles by Sec24a. BMC Biochem 16:16
Johnson, Adam; Bhattacharya, Nilakshee; Hanna, Michael et al. (2015) TFG clusters COPII-coated transport carriers and promotes early secretory pathway organization. EMBO J 34:811-27
Hariri, Hanaa; Bhattacharya, Nilakshee; Johnson, Kerri et al. (2014) Insights into the mechanisms of membrane curvature and vesicle scission by the small GTPase Sar1 in the early secretory pathway. J Mol Biol 426:3811-3826

Showing the most recent 10 out of 15 publications