Sar1 GTPase Activity Is Regulated by Membrane Curvature
Hanna, Michael G
Chapman, Edwin R
The Journal of Biological Chemistry
American Society for Biochemistry and Molecular Biology
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Hanna, M. G., Mela, I., Wang, L., Henderson, R., Chapman, E. R., Edwardson, M., & Audhya, A. (2015). Sar1 GTPase Activity Is Regulated by Membrane Curvature. The Journal of Biological Chemistry, 291 1014-1027. https://doi.org/10.1074/jbc.M115.672287
The majority of biosynthetic secretory proteins initiate their journey through the endomembrane system from specific subdomains of the endoplasmic reticulum (ER). At these locations, coated transport carriers are generated, with the Sar1 GTPase playing a critical role in membrane bending, recruitment of coat components, and nascent vesicle formation. How these events are appropriately coordinated remains poorly understood. Here, we demonstrate that Sar1 acts as the curvature sensing component of the COPII coat complex and highlight the ability of Sar1 to bind more avidly to membranes of high curvature. Additionally, using an atomic force microscopy-based approach, we further show that the intrinsic GTPase activity of Sar1 is necessary for remodeling lipid bilayers. Consistent with this idea, Sar1-mediated membrane remodeling is dramatically accelerated in the presence of its guanine nucleotide activating protein (GAP), Sec23-Sec24, and blocked upon addition of GMP-PNP, a poorly hydrolysable analog of GTP. Our results also indicate that Sar1 GTPase activity is stimulated by membranes that exhibit elevated curvature, potentially enabling Sar1 membrane scission activity to be spatially restricted to highly bent membranes that are characteristic of a bud neck. Taken together, our data support a stepwise model in which the amino-terminal amphipathic helix of GTP-bound Sar1 stably penetrates the ER membrane, promoting local membrane deformation. As membrane bending increases, Sar1 membrane binding is elevated, ultimately culminating in GTP hydrolysis, which may destabilize the bilayer sufficiently to facilitate membrane fission.
COPII, endoplasmic reticulum (ER), GTPase, membrane bilayer, membrane transport
This work was supported by grants from the NIH (GM110567 and GM088151 to AA). IM, RMH and JME were supported by a grant from the Biotechnology and Biological Sciences Research Council (BB/J018236/1). ERC is an Investigator of the Howard Hughes Medical Institute. We thank Elizabeth Miller for providing purified yeast COPII components, Subhanjan Mondal and Said Goueli at Promega Corporation for providing us access to the GTPase-Glo system ahead of release, and members of the Audhya lab for critically reading this manuscript.
External DOI: https://doi.org/10.1074/jbc.M115.672287
This record's URL: https://www.repository.cam.ac.uk/handle/1810/252909
Attribution 2.0 UK: England & Wales
Licence URL: http://creativecommons.org/licenses/by/2.0/uk/