title: Membrane-proximal tryptophans of synaptobrevin II stabilize priming of secretory vesicles.
abstract: Trans-soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) complexes formed between the SNARE motifs of synaptobrevin II, SNAP-25, and syntaxin play an essential role in Ca(2+)-regulated exocytosis. Apart from the well studied interactions of the SNARE domains, little is known about the functional relevance of other evolutionarily conserved structures in the SNARE proteins. Here, we show that substitution of two highly conserved tryptophan residues within the juxtamembrane domain (JMD) of the vesicular SNARE Synaptobrevin II (SybII) profoundly impairs priming of granules in mouse chromaffin cells without altering catecholamine release from single vesicles. Using molecular dynamic simulations of membrane-embedded SybII, we show that Trp residues of the JMD influence the electrostatic surface potential by controlling the position of neighboring lysine and arginine residues at the membrane-water interface. Our observations indicate a decisive role of the tryptophan moiety of SybII in keeping the vesicles in the release-ready state and support a model wherein tryptophan-mediated protein-lipid interactions assist in bridging the apposing membranes before fusion.
authors.affiliation: Institute for Physiology, School of Medicine, University of Saarland, D-66421 Homburg/Saar, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Borisovska
authors.forename: Yvonne N
authors.initials: YN
authors.lastname: Schwarz
authors.forename: Madhurima
authors.initials: M
authors.lastname: Dhara
authors.forename: Antonio
authors.initials: A
authors.lastname: Yarzagaray
authors.forename: Sandra
authors.initials: S
authors.lastname: Hugo
authors.forename: Daniele
authors.initials: D
authors.lastname: Narzi
authors.forename: Shirley W I
authors.initials: SW
authors.lastname: Siu
authors.forename: Jaideep
authors.initials: J
authors.lastname: Kesavan
authors.forename: Ralf
authors.initials: R
authors.lastname: Mohrmann
authors.forename: Rainer A
authors.initials: RA
authors.lastname: Böckmann
authors.forename: Dieter
authors.initials: D
authors.lastname: Bruns
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D005089:Exocytosis / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D050600:SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism*; D014364:Tryptophan / Q000235:genetics / Q000378:metabolism*; D050988:Vesicle-Associated Membrane Protein 2 / Q000235:genetics / Q000378:metabolism*
chemical_list: D050600:SNARE Proteins; D050988:Vesicle-Associated Membrane Protein 2; C494808:vesicle-associated membrane protein 2, mouse; D014364:Tryptophan