title: Identification of synapsin I peptides that insert into lipid membranes.
abstract: The synapsins constitute a family of synaptic vesicle-associated phosphoproteins essential for regulating neurotransmitter release and synaptogenesis. The molecular mechanisms underlying the selective targeting of synapsin I to synaptic vesicles are thought to involve specific protein-protein interactions, while the high-affinity binding to the synaptic vesicle membrane may involve both protein-protein and protein-lipid interactions. The highly hydrophobic N-terminal region of the protein has been shown to bind with high affinity to the acidic phospholipids phosphatidylserine and phosphatidylinositol and to penetrate the hydrophobic core of the lipid bilayer. To precisely identify the domains of synapsin I which mediate the interaction with lipids, synapsin I was bound to liposomes containing the membrane-directed carbene-generating reagent 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine and subjected to photolysis. Isolation and N-terminal amino acid sequencing of 125I-labelled synapsin I peptides derived from CNBr cleavage indicated that three distinct regions in the highly conserved domain C of synapsin I insert into the hydrophobic core of the phospholipid bilayer. The boundaries of the regions encompass residues 166-192, 233-258 and 278-327 of bovine synapsin I. These regions are surface-exposed in the crystal structure of domain C of bovine synapsin I and are evolutionarily conserved among isoforms across species. The present data offer a molecular explanation for the high-affinity binding of synapsin I to phospholipid bilayers and synaptic vesicles.
authors.affiliation: Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Cheetham
authors.forename: S
authors.initials: S
authors.lastname: Hilfiker
authors.forename: F
authors.initials: F
authors.lastname: Benfenati
authors.forename: T
authors.initials: T
authors.lastname: Weber
authors.forename: P
authors.initials: P
authors.lastname: Greengard
authors.forename: A J
authors.initials: AJ
authors.lastname: Czernik
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D019143:Evolution, Molecular; D008051:Lipid Bilayers; D008081:Liposomes; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D016704:Synapsins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D008051:Lipid Bilayers; D008081:Liposomes; D010446:Peptide Fragments; D010743:Phospholipids; D016704:Synapsins