title: Comparative analysis of Drosophila and mammalian complexins as fusion clamps and facilitators of neurotransmitter release.
abstract: The SNARE-binding protein complexin (Cpx) has been demonstrated to regulate synaptic vesicle fusion. Previous studies are consistent with Cpx functioning either as a synaptic vesicle fusion clamp to prevent premature exocytosis, or as a facilitator to directly stimulate release. Here we examined conserved roles of invertebrate and mammalian Cpx isoforms in the regulation of neurotransmitter release using the Drosophila neuromuscular junction as a model synapse. We find that SNARE binding by Cpx is required for its role as a fusion clamp. All four mammalian Cpx proteins (mCpx), which have been demonstrated to facilitate release, also function as fusion clamps when expressed in Drosophila cpx null mutants, though their clamping abilities vary between isoforms. Moreover, expression of mCpx I, II or III isoforms dramatically enhance evoked release compared to mCpx IV or Drosophila Cpx. Differences in the clamping and facilitating properties of complexin isoforms can be partially attributed to differences in the C-terminal membrane tethering domain. Our findings indicate that the function of complexins as fusion clamps and facilitators of fusion are conserved across evolution, and that these roles are genetically separable within an isoform and across different isoforms.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. rcho@mit.edu
authors.forename: Richard W
authors.initials: RW
authors.lastname: Cho
authors.forename: Yun
authors.initials: Y
authors.lastname: Song
authors.forename: J Troy
authors.initials: JT
authors.lastname: Littleton
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D004330:Drosophila; D005089:Exocytosis / Q000502:physiology*; D007150:Immunohistochemistry; D008322:Mammals; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009469:Neuromuscular Junction; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010802:Phylogeny; D020033:Protein Isoforms / Q000378:metabolism; D050600:SNARE Proteins / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism*
chemical_list: D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D020033:Protein Isoforms; D050600:SNARE Proteins