Complexin Controls the Force Transfer from SNARE Complexes to Membranes in Fusion

Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
Science (Impact Factor: 33.61). 02/2009; 323(5913):516-21. DOI: 10.1126/science.1166505
Source: PubMed


Trans–SNAP receptor (SNARE, where SNAP is defined as soluble NSF attachment protein, and NSF is defined as N-ethylmaleimide–sensitive factor) complexes catalyze synaptic vesicle fusion and bind complexin, but the function of complexin
binding to SNARE complexes remains unclear. Here we show that in neuronal synapses, complexin simultaneously suppressed spontaneous
fusion and activated fast calcium ion–evoked fusion. The dual function of complexin required SNARE binding and also involved
distinct amino-terminal sequences of complexin that localize to the point where trans-SNARE complexes insert into the fusing
membranes, suggesting that complexin controls the force that trans-SNARE complexes apply onto the fusing membranes. Consistent
with this hypothesis, a mutation in the membrane insertion sequence of the v-SNARE synaptobrevin/vesicle-associated membrane
protein (VAMP) phenocopied the complexin loss-of-function state without impairing complexin binding to SNARE complexes. Thus,
complexin probably activates and clamps the force transfer from assembled trans-SNARE complexes onto fusing membranes.

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    • "Further structure/function analysis replacing endogenous syntaxin-3 by a non complexin-binding mutant confirmed that syntaxin-3/complexin interaction is necessary for the function of postsynaptic SNARE complexes implicated in AMPARs exocytosis . These results suggest that postsynaptic syntaxin-3 via complexins may constitutively restrict AMPARs insertion until calcium influx reaches the postsynaptic compartment in a similar fashion to their function at presynaptic terminals (Giraudo et al., 2006; Tang et al., 2006; Huntwork and Littleton, 2007; Maximov et al., 2009; Xue et al., 2009; Yang et al., 2010). Furthermore, in a manner analogous to syntaxin-1 in presynaptic terminals, syntaxin-3 was shown to require the binding of SM proteins. "
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    ABSTRACT: Sorting endosomes carry α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPARs) from their maturation sites to their final destination at the dendritic plasma membrane through both constitutive and regulated exocytosis. Insertion of functional AMPARs into the postsynaptic membrane is essential for maintaining fast excitatory synaptic transmission and plasticity. Despite this crucial role in neuronal function, the machinery mediating the fusion of AMPAR-containing endosomes in dendrites has been largely understudied in comparison to presynaptic vesicle exocytosis. Increasing evidence suggests that similarly to neurotransmitter release, AMPARs insertion relies on the formation of a SNARE complex (soluble NSF-attachment protein receptor), whose composition in dendrites has just begun to be elucidated. This review analyzes recent findings of the fusion machinery involved in regulated AMPARs insertion and discusses how dendritic exocytosis and AMPARs lateral diffusion may work together to support synaptic plasticity.
    Frontiers in Cellular Neuroscience 12/2014; 8:407. DOI:10.3389/fncel.2014.00407 · 4.29 Impact Factor
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    • "Primary cell cultures were prepared from hippocampus of P0 mouse pups as described earlier (Maximov et al., 2009; Mukherjee et al., 2010). Briefly, cells were dissociated by papain digestion, plated on polylysine-coated glass coverslips and cultured in modified Eagle's medium (Invitrogen, "
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    ABSTRACT: Signal transduction and neurotransmitter release in the vertebrate central nervous system are confined to the structurally complex presynaptic electron dense projections called "active zones." Although the nature of these projections remains a mystery, genetic and biochemical work has provided evidence for the active zone (AZ) associated proteins i.e. Piccolo/Aczonin, Bassoon, RIM1/Unc10, Munc13/Unc13, Liprin-α/SYD2/Dliprin and ELKS/CAST/BRP and their specific molecular functions. It still remains unclear, however, what their precise contribution is to the AZ assembly. In our project, we studied in Wistar rats the temporal and spatial distribution of AZ proteins and their colocalization with Synaptophysin in the developing cerebellar cortex at key stages of cerebellum neurogenesis. Our study demonstrated that AZ proteins were already present at the very early stages of cerebellar neurogenesis and exhibited distinct spatial and temporal variations in immunoexpression throughout the course of the study. Colocalization analysis revealed that the colocalization pattern was time-dependent and different for each studied protein. The highest collective mean percentage of colocalization (>85%) was observed at postnatal day (PD) 5, followed by PD10 (>83%) and PD15 (>80%). The findings of our study shed light on AZ protein immunoexpression changes during cerebellar cortex neurogenesis and help frame a hypothetical model of AZ assembly.
    Acta histochemica 02/2013; 115(6). DOI:10.1016/j.acthis.2013.01.003 · 1.71 Impact Factor
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    • "Our discovery of the immediate fusion pathway (point contact to full fusion) raised the hypothesis that for neurotransmitter release, other synaptic proteins introduce a preference for this immediate pathway upon Ca 2+ -triggering. We confirmed this hypothesis by observing that complexin (in combination with SNAREs and synaptotagmin 1) favors this immediate fusion pathway upon Ca 2+ triggering, a result that correlates well with complexin's activating role in vivo for synchronous release upon an action potential (Maximov et al., 2009). Specifically, we observed that complexin significantly increased the number of immediate fusion events that occur right upon Ca 2+ -injection (Figure 6). "
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    ABSTRACT: The molecular underpinnings of synaptic vesicle fusion for fast neurotransmitter release are still unclear. Here, we used a single vesicle–vesicle system with reconstituted SNARE and synaptotagmin-1 proteoliposomes to decipher the temporal sequence of membrane states upon Ca2+-injection at 250–500 μM on a 100-ms timescale. Furthermore, detailed membrane morphologies were imaged with cryo-electron microscopy before and after Ca2+-injection. We discovered a heterogeneous network of immediate and delayed fusion pathways. Remarkably, all instances of Ca2+-triggered immediate fusion started from a membrane–membrane point-contact and proceeded to complete fusion without discernible hemifusion intermediates. In contrast, pathways that involved a stable hemifusion diaphragm only resulted in fusion after many seconds, if at all. When complexin was included, the Ca2+-triggered fusion network shifted towards the immediate pathway, effectively synchronizing fusion, especially at lower Ca2+-concentration. Synaptic proteins may have evolved to select this immediate pathway out of a heterogeneous network of possible membrane fusion pathways. DOI:
    eLife Sciences 12/2012; 1(1):e00109. DOI:10.7554/eLife.00109 · 9.32 Impact Factor
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