The In Vivo Architecture of the Exocyst Provides Structural Basis for Exocytosis
Andrea Picco5, Ibai Irastorza-Azcarate5, Tanja Specht, Dominik Böke, Irene Pazos, Anne-Sophie Rivier-Cordey, Damien P. Devos, Marko Kakson, Oriol Gallego6,
5Co-first author
6Lead Contact
Article Info
Publication History
Published: January 26, 2017 Accepted: January 5, 2017 Received in revised form: October 18, 2016 Received: February 9, 2016
Highlights
• An integrative approach reconstructs protein complexes in 3D through live-cell imaging
• We use this approach to reconstruct the exocyst complex bound to a vesicle in vivo
• Exocyst is a stable complex and regulatory proteins target its multimerization site
• We model how exocyst binds the vesicle allowing its contact with the plasma membrane
Summary
The structural characterization of protein complexes in their native environment is challenging but crucial for understanding the mechanisms that mediate cellular processes. We developed an integrative approach to reconstruct the 3D architecture of protein complexes in vivo. We applied this approach to the exocyst, a hetero-octameric complex of unknown structure that is thought to tether secretory vesicles during exocytosis with a poorly understood mechanism. We engineered yeast cells to anchor the exocyst on defined landmarks and determined the position of its subunit termini at nanometer precision using fluorescence microscopy. We then integrated these positions with the structural properties of the subunits to reconstruct the exocyst together with a vesicle bound to it. The exocyst has an open hand conformation made of rod-shaped subunits that are interlaced in the core. The exocyst architecture explains how the complex can tether secretory vesicles, placing them in direct contact with the plasma membrane.
Keywords:
Vesicle trafficking, exocytosis, exocyst, fluorescence microscopy, fluorescence localization, integrative structural biology, architecture of protein complexes, in vivo structure, PICT, SHREC.
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