Interaction of the complexin accessory helix with the C-terminus of the SNARE complex: molecular-dynamics model of the fusion clamp.
SNARE complexes form between the synaptic vesicle protein synaptobrevin and the plasma membrane proteins syntaxin and SNAP25 to drive membrane fusion. A cytosolic protein, complexin (Cpx), binds to the SNARE bundle, and its accessory helix (AH) functions to clamp synaptic vesicle fusion. We performed molecular-dynamics simulations of the SNARE/Cpx complex and discovered that at equilibrium the Cpx AH forms tight links with both synaptobrevin and SNAP25. To simulate the effect of electrostatic repulsion between vesicle and membrane on the SNARE complex, we calculated the electrostatic force and performed simulations with an external force applied to synaptobrevin. We found that the partially unzipped state of the SNARE bundle can be stabilized by interactions with the Cpx AH, suggesting a simple mechanistic explanation for the role of Cpx in fusion clamping. To test this model, we performed experimental and computational characterizations of the syx(3-69)Drosophila mutant, which has a point mutation in syntaxin that causes increased spontaneous fusion. We found that this mutation disrupts the interaction of the Cpx AH with synaptobrevin, partially imitating the cpx null phenotype. Our results support a model in which the Cpx AH clamps fusion by binding to the synaptobrevin C-terminus, thus preventing full SNARE zippering.
Neuroscience Department, Universidad Central del Caribe, Bayamon, Puerto Rico. mb.ucdelcaribe@gmail.com
Maria
M
Bykhovskaia
Anand
A
Jagota
Agustin
A
Gonzalez
Alexander
A
Vasin
J Troy
JT
Littleton
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D004330:Drosophila / Q000737:chemistry / Q000378:metabolism; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008561:Membrane Fusion; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D017354:Point Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D050600:SNARE Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism / Q000502:physiology; D009435:Synaptic Transmission; D013572:Synaptic Vesicles / Q000378:metabolism
D029721:Drosophila Proteins; D050600:SNARE Proteins