title: Functional role of ATP binding to synapsin I in synaptic vesicle trafficking and release dynamics.
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.
authors.affiliation: Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, 16163 Genova, Italy, and.
authors.forename: Marta
authors.initials: M
authors.lastname: Orlando
authors.affiliation: Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, 16163 Genova, Italy, and.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Lignani
authors.affiliation: Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, 16163 Genova, Italy, and.
authors.forename: Luca
authors.initials: L
authors.lastname: Maragliano
authors.affiliation: Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, 16163 Genova, Italy, and Department of Experimental Medicine, University of Genova, 16132, Genova, Italy.
authors.forename: Anna
authors.identifier: http://orcid.org/0000-0002-8801-038X
authors.initials: A
authors.lastname: Fassio
authors.affiliation: Department of Experimental Medicine, University of Genova, 16132, Genova, Italy.
authors.forename: Franco
authors.initials: F
authors.lastname: Onofri
authors.affiliation: Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, 16163 Genova, Italy, and Department of Experimental Medicine, University of Genova, 16132, Genova, Italy.
authors.forename: Pietro
authors.identifier: http://orcid.org/0000-0001-9599-3436
authors.initials: P
authors.lastname: Baldelli
authors.affiliation: Department of Experimental Medicine, University of Genova, 16132, Genova, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Giovedí
authors.affiliation: 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.
authors.forename: Fabio
authors.identifier: http://orcid.org/0000-0002-0653-8368
authors.initials: F
authors.lastname: Benfenati
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D005089:Exocytosis / Q000502:physiology*; D005260:Female; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009474:Neurons / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000378:metabolism* / Q000648:ultrastructure; D016704:Synapsins / Q000235:genetics / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology; D013572:Synaptic Vesicles / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D016704:Synapsins; D000255:Adenosine Triphosphate
keywords: ATP binding; inhibitory transmission; molecular dynamics simulations; synapsins; synaptic ultrastructure; synaptic vesicles