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Title: The Structure of the Exocyst Subunit Sec6p Defines a Conserved Architecture with Diverse Roles

Abstract

The exocyst is a conserved protein complex essential for trafficking secretory vesicles to the plasma membrane. The structure of the C-terminal domain of the exocyst subunit Sec6p reveals multiple helical bundles, which are structurally and topologically similar to Exo70p and the C-terminal domains of Exo84p and Sec15, despite <10% sequence identity. The helical bundles appear to be evolutionarily related molecular scaffolds that have diverged to create functionally distinct exocyst proteins.

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
914356
Report Number(s):
BNL-78924-2007-JA
TRN: US200809%%198
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nat. Struct. Mol. Biol.; Journal Volume: 13; Journal Issue: 6
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; PLASMA; PROTEINS; PROTEIN STRUCTURE; national synchrotron light source

Citation Formats

Mylavarapu,S., Furgason, M., Brewer, D., and Munson, M. The Structure of the Exocyst Subunit Sec6p Defines a Conserved Architecture with Diverse Roles. United States: N. p., 2006. Web.
Mylavarapu,S., Furgason, M., Brewer, D., & Munson, M. The Structure of the Exocyst Subunit Sec6p Defines a Conserved Architecture with Diverse Roles. United States.
Mylavarapu,S., Furgason, M., Brewer, D., and Munson, M. Sun . "The Structure of the Exocyst Subunit Sec6p Defines a Conserved Architecture with Diverse Roles". United States. doi:.
@article{osti_914356,
title = {The Structure of the Exocyst Subunit Sec6p Defines a Conserved Architecture with Diverse Roles},
author = {Mylavarapu,S. and Furgason, M. and Brewer, D. and Munson, M.},
abstractNote = {The exocyst is a conserved protein complex essential for trafficking secretory vesicles to the plasma membrane. The structure of the C-terminal domain of the exocyst subunit Sec6p reveals multiple helical bundles, which are structurally and topologically similar to Exo70p and the C-terminal domains of Exo84p and Sec15, despite <10% sequence identity. The helical bundles appear to be evolutionarily related molecular scaffolds that have diverged to create functionally distinct exocyst proteins.},
doi = {},
journal = {Nat. Struct. Mol. Biol.},
number = 6,
volume = 13,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • The exocyst complex regulates the last steps of exocytosis, which is essential to organisms across kingdoms. In humans, its dysfunction is correlated with several significant diseases, such as diabetes and cancer progression. Investigation of the dynamic regulation of the evolutionarily conserved exocyst-related processes using mutants in genetically tractable organisms such as Arabidopsis thaliana is limited by the lethality or the severity of phenotypes. We discovered that the small molecule Endosidin2 (ES2) binds to the EXO70 (exocyst component of 70 kDa) subunit of the exocyst complex, resulting in inhibition of exocytosis and endosomal recycling in both plant and human cells andmore » enhancement of plant vacuolar trafficking. An EXO70 protein with a C-terminal truncation results in dominant ES2 resistance, uncovering possible distinct regulatory roles for the N terminus of the protein. Ultimately, this study not only provides a valuable tool in studying exocytosis regulation but also offers a potentially new target for drugs aimed at addressing human disease.« less
  • The exocyst is an evolutionarily conserved octameric complex involved in polarized exocytosis from yeast to humans. The Sec3 subunit of the exocyst acts as a spatial landmark for exocytosis through its ability to bind phospholipids and small GTPases. The structure of the N-terminal domain of Sec3 (Sec3N) was determined ab initio and defines a new subclass of pleckstrin homology (PH) domains along with a new family of proteins carrying this domain. Respectively, N- and C-terminal to the PH domain Sec3N presents an additional {alpha}-helix and two {beta}-strands that mediate dimerization through domain swapping. The structure identifies residues responsible for phospholipidmore » binding, which when mutated in cells impair the localization of exocyst components at the plasma membrane and lead to defects in exocytosis. Through its ability to bind the small GTPase Cdc42 and phospholipids, the PH domain of Sec3 functions as a coincidence detector at the plasma membrane.« less
  • Voltage-gated sodium channels (Nav) produce sodium currents that underlie the initiation and propagation of action potentials in nerve and muscle cells. Fibroblast growth factor homologous factors (FHFs) bind to the intracellular C-terminal region of the Nav alpha subunit to modulate fast inactivation of the channel. In this study we solved the crystal structure of a 149-residue-long fragment of human FHF2A which unveils the structural features of the homology core domain of all 10 human FHF isoforms. Through analysis of crystal packing contacts and site-directed mutagenesis experiments we identified a conserved surface on the FHF core domain that mediates channel bindingmore » in vitro and in vivo. Mutations at this channel binding surface impaired the ability of FHFs to co-localize with Navs at the axon initial segment of hippocampal neurons. The mutations also disabled FHF modulation of voltage-dependent fast inactivation of sodium channels in neuronal cells. Based on our data, we propose that FHFs constitute auxiliary subunits for Navs.« less
  • The exocyst is a large complex that is required for tethering vesicles at the final stages of the exocytic pathway in all eukaryotes. Here we present the structures of the Exo70p subunit of this complex and of the C-terminal domains of Exo84p, at 2.0-Angstrom and 2.85-Angstrom resolution, respectively. Exo70p forms a 160-Angstrom-long rod with a novel fold composed of contiguous {alpha}-helical bundles. The Exo84p C terminus also forms a long rod (80 Angstroms), which unexpectedly has the same fold as the Exo70p N terminus. Our structural results and our experimental observations concerning the interaction between Exo70p and other exocyst subunitsmore » or Rho3p GTPase are consistent with an architecture wherein exocyst subunits are composed of mostly helical modules strung together into long rods.« less