title: The synaptotagmin juxtamembrane domain is involved in neuroexocytosis.
abstract: Synaptotagmin is a synaptic vesicle membrane protein which changes conformation upon Ca(2+) binding and triggers the fast neuroexocytosis that takes place at synapses. We have synthesized a series of peptides corresponding to the sequence of the cytosolic juxtamembrane domain of synaptotagmin, which is highly conserved among different isoforms and animal species, with or without either a hexyl hydrophobic chain or the hexyl group plus a fluorescein moiety. We show that these peptides inhibit neurotransmitter release, that they localize on the presynaptic membrane of the motor axon terminal at the neuromuscular junction and that they bind monophosphoinositides in a Ca(2+)-independent manner. Based on these findings, we propose that the juxtamembrane cytosolic domain of synaptotagmin binds the cytosolic layer of the presynaptic membrane at rest. This binding brings synaptic vesicles and plasma membrane in a very close apposition, favouring the formation of hemifusion intermediates that enable rapid vesicle fusion.
authors.affiliation: Dipartimento di Scienze Biomediche, Università di Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Caccin
authors.affiliation: Dipartimento di Scienze Biomediche, Università di Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Scorzeto
authors.affiliation: CRIBI Biotechnology Centre, Via Ugo Bassi 58/B, 35131 Padova, Italy.
authors.forename: Nunzio
authors.initials: N
authors.lastname: Damiano
authors.affiliation: Dipartimento di Scienze Biomediche, Università di Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy ; CRIBI Biotechnology Centre, Via Ugo Bassi 58/B, 35131 Padova, Italy.
authors.forename: Oriano
authors.initials: O
authors.lastname: Marin
authors.affiliation: Dipartimento di Scienze Biomediche, Università di Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy.
authors.forename: Aram
authors.initials: A
authors.lastname: Megighian
authors.affiliation: Dipartimento di Scienze Biomediche, Università di Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy ; Institute for Neuroscience, National Research Council, Via Ugo Bassi 58/B, 35131 Padova, Italy.
authors.forename: Cesare
authors.initials: C
authors.lastname: Montecucco
keywords: Anionic phospholipids; JMS, juxtamembrane segment; Juxtamembrane domain; NMJ, neuromuscular junction; Neuroexocytosis; Neuromuscular junction; PM, presynaptic membrane; SV, synaptic vesicles; Synaptotagmin; Syt, synaptotagmin; TM, transmembrane; h-FJMS, hexyl fluorescent juxtamembrane segment; h-JMS, hexyl juxtamembrane segment; h-sJMS, hexyl scrambled juxtamembrane segment; α-BTX, alpha-bungarotoxin