Format

Send to

Choose Destination
J Mol Biol. 2014 Nov 11;426(22):3811-3826. doi: 10.1016/j.jmb.2014.08.023. Epub 2014 Sep 2.

Insights into the mechanisms of membrane curvature and vesicle scission by the small GTPase Sar1 in the early secretory pathway.

Author information

1
Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA. Electronic address: hhh09c@my.fsu.edu.
2
Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA. Electronic address: nb02c@fsu.edu.
3
Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA. Electronic address: kmj09e@my.fsu.edu.
4
Department of Physics, Florida State University, Tallahassee, FL 32306, USA. Electronic address: ajn10d@fsu.edu.
5
Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA; Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA. Electronic address: sstagg@fsu.edu.

Abstract

The small GTPase protein Sar1 is known to be involved in both the initiation of COPII-coated vesicle formation and scission of the nascent vesicle from the endoplasmic reticulum. The molecular details for the mechanism of membrane remodeling by Sar1 remain unresolved. Here, we show that Sar1 transforms synthetic liposomes into structures of different morphologies including tubules and detached vesicles. We demonstrate that Sar1 alone is competent for vesicle scission in a manner that depends on the concentration of Sar1 molecules occupying the membrane. Sar1 molecules align on low-curvature membranes to form an extended lattice. The continuity of this lattice breaks down as the curvature locally increases. The smallest repeating unit constituting the ordered lattice is a Sar1 dimer. The three-dimensional structure of the Sar1 lattice was reconstructed by substituting spherical liposomes with galactoceramide lipid tubules of homogeneous diameter. These data suggest that Sar1 dimerization is responsible for the formation of constrictive membrane curvature. We propose a model whereby Sar1 dimers assemble into ordered arrays to promote membrane constriction and COPII-directed vesicle scission.

KEYWORDS:

ADE model; N-terminal helix; Sar1 lattice; dimerization; membrane scission

PMID:
25193674
PMCID:
PMC4254083
DOI:
10.1016/j.jmb.2014.08.023
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for Elsevier Science Icon for PubMed Central
Loading ...
Support Center