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

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

Author information

1
Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, 16163 Genova, Italy, and.
2
Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, 16163 Genova, Italy, and Department of Experimental Medicine, University of Genova, 16132, Genova, Italy.
3
Department of Experimental Medicine, University of Genova, 16132, Genova, Italy.
4
Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, 16163 Genova, Italy, and Department of Experimental Medicine, University of Genova, 16132, Genova, Italy fabio.benfenati@iit.it.

Abstract

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

PMID:
25355227
PMCID:
PMC6608424
DOI:
10.1523/JNEUROSCI.1093-14.2014
[Indexed for MEDLINE]
Free PMC Article

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