title: Homotetrameric structure of the SNAP-23 N-terminal coiled-coil domain.
abstract: SNARE proteins mediate intracellular membrane fusion by forming a coiled-coil complex to merge opposing membranes. A "fusion-active" neuronal SNARE complex is a parallel four-helix bundle containing two coiled-coil domains from SNAP-25 and one coiled-coil domain each from syntaxin-1a and VAMP-2. "Prefusion" assembly intermediate complexes can also form from these SNAREs. We studied the N-terminal coiled-coil domain of SNAP-23 (SNAP-23N), a non-neuronal homologue of SNAP-25, and its interaction with other coiled-coil domains. SNAP-23N can assemble spontaneously with the coiled-coil domains from SNAP-23C, syntaxin-4, and VAMP-3 to form a heterotetrameric complex. Unexpectedly, pure SNAP-23N crystallizes as a coiled-coil homotetrameric complex. The four helices have a parallel orientation and are symmetrical about the long axis. The complex is stabilized through the interaction of conserved hydrophobic residues comprising the a and d positions of the coiled-coil heptad repeats. In addition, a central, highly conserved glutamine residue (Gln-48) is buried within the interface by hydrogen bonding between glutamine side chains derived from adjacent subunits and to solvent molecules. A comparison of the SNAP-23N structure to other SNARE complex structures reveals how a simple coiled-coil motif can form diverse SNARE complexes.
authors.affiliation: Division of Hemostasis and Thrombosis, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02115, USA. sfreedm2@caregroup.harvard.edu
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Freedman
authors.forename: Hyun Kyu
authors.initials: HK
authors.lastname: Song
authors.forename: Yingwu
authors.initials: Y
authors.lastname: Xu
authors.forename: Zhen-Yu J
authors.initials: ZY
authors.lastname: Sun
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Eck
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000648:ultrastructure; D018360:Crystallography, X-Ray; D006801:Humans; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D011994:Recombinant Proteins / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D002352:Carrier Proteins; D046911:Macromolecular Substances; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D011994:Recombinant Proteins; C100493:SNAP23 protein, human