Functional role of ATP binding to synapsin I in synaptic vesicle trafficking and release dynamics

J Neurosci. 2014 Oct 29;34(44):14752-68. doi: 10.1523/JNEUROSCI.1093-14.2014.


Synapsins (Syns) are synaptic vesicle (SV)-associated proteins involved in the regulation of synaptic transmission and plasticity, which display a highly conserved ATP binding site in the central C-domain, whose functional role is unknown. Using molecular dynamics simulations, we demonstrated that ATP binding to SynI is mediated by a conformational transition of a flexible loop that opens to make the binding site accessible; such transition, prevented in the K269Q mutant, is not significantly affected in the absence of Ca(2+) or by the E373K mutation that abolishes Ca(2+)-binding. Indeed, the ATP binding to SynI also occurred under Ca(2+)-free conditions and increased its association with purified rat SVs regardless of the presence of Ca(2+) and promoted SynI oligomerization. However, although under Ca(2+)-free conditions, SynI dimerization and SV clustering were enhanced, Ca(2+) favored the formation of tetramers at the expense of dimers and did not affect SV clustering, indicating a role of Ca(2+)-dependent dimer/tetramer transitions in the regulation of ATP-dependent SV clustering. To elucidate the role of ATP/SynI binding in synaptic physiology, mouse SynI knock-out hippocampal neurons were transduced with either wild-type or K269Q mutant SynI and inhibitory transmission was studied by patch-clamp and electron microscopy. K269Q-SynI expressing inhibitory synapses showed increased synaptic strength due to an increase in the release probability, an increased vulnerability to synaptic depression and a dysregulation of SV trafficking, when compared with wild-type SynI-expressing terminals. The results suggest that the ATP-SynI binding plays predocking and postdocking roles in the modulation of SV clustering and plasticity of inhibitory synapses.

Keywords: ATP binding; inhibitory transmission; molecular dynamics simulations; synapsins; synaptic ultrastructure; synaptic vesicles.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism*
  • Animals
  • Exocytosis / physiology*
  • Female
  • Hippocampus / cytology
  • Hippocampus / metabolism
  • Hippocampus / ultrastructure
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Neurons / cytology
  • Neurons / metabolism*
  • Neurons / ultrastructure
  • Protein Transport / physiology
  • Rats
  • Rats, Sprague-Dawley
  • Synapses / metabolism*
  • Synapses / ultrastructure
  • Synapsins / genetics
  • Synapsins / metabolism*
  • Synaptic Transmission / physiology
  • Synaptic Vesicles / metabolism*
  • Synaptic Vesicles / ultrastructure


  • Synapsins
  • Adenosine Triphosphate