Symmetrical organization of proteins under docked synaptic vesicles

FEBS Lett. 2019 Jan;593(2):144-153. doi: 10.1002/1873-3468.13316. Epub 2019 Jan 18.

Abstract

During calcium-regulated exocytosis, the constitutive fusion machinery is 'clamped' in a partially assembled state until synchronously released by calcium. The protein machinery involved in this process is known, but the supra-molecular architecture and underlying mechanisms are unclear. Here, we use cryo-electron tomography analysis in nerve growth factor-differentiated neuro-endocrine (PC12) cells to delineate the organization of the release machinery under the docked vesicles. We find that exactly six exocytosis modules, each likely consisting of a single SNAREpin with its bound Synaptotagmins, Complexin, and Munc18 proteins, are symmetrically arranged at the vesicle-PM interface. Mutational analysis suggests that the symmetrical organization is templated by circular oligomers of Synaptotagmin. The observed arrangement, including its precise radial positioning, is in-line with the recently proposed 'buttressed ring hypothesis'.

Keywords: PC12 cells; SNARE proteins; cryo-electron tomography; regulated exocytosis; synaptotagmin.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Cryoelectron Microscopy
  • Electron Microscope Tomography
  • Exocytosis
  • Munc18 Proteins / genetics
  • Munc18 Proteins / metabolism*
  • Mutation
  • Nerve Growth Factor / pharmacology
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism
  • Neurites / drug effects
  • Neurites / metabolism
  • PC12 Cells
  • Rats
  • SNARE Proteins / genetics
  • SNARE Proteins / metabolism*
  • Synaptic Vesicles / chemistry*
  • Synaptic Vesicles / genetics
  • Synaptic Vesicles / metabolism
  • Synaptotagmins / genetics
  • Synaptotagmins / metabolism*

Substances

  • Munc18 Proteins
  • Nerve Tissue Proteins
  • SNARE Proteins
  • Synaptotagmins
  • Nerve Growth Factor
  • Calcium

Associated data

  • PDB/5W5C
  • PDB/4JEU