UNC-13 interaction with syntaxin is required for synaptic transmission.
Neurotransmitter secretion at synapses is controlled by several processes-morphological docking of vesicles at release sites, priming of docked vesicles to make them fusion competent, and calcium-dependent fusion of vesicles with the plasma membrane . In worms, flies, and mice, mutants lacking UNC-13 have defects in vesicle priming . Current models propose that UNC-13 primes vesicles by stabilizing Syntaxin's "open" conformation by directly interacting with its amino-terminal regulatory domain . However, the functional significance of the UNC-13/Syntaxin interaction has not been tested directly. A truncated protein containing the Munc homology domains (MHD1 and MHD2) and the carboxy-terminal C2 domain partially rescued both the behavioral and secretion defects of unc-13 mutants in C. elegans. A double mutation in MHD2 (F1000A/K1002A) disrupts the UNC-13/Syntaxin interaction. The rate of endogenous synaptic events and the amplitude of nerve-evoked excitatory post-synaptic currents (EPSCs) were both significantly reduced in UNC-13S(F1000A/K1002A). However, the pool of primed (i.e., fusion-competent) vesicles was normal. These results suggest that the UNC-13/Syntaxin interaction is conserved in C. elegans and that, contrary to current models, the UNC-13/Syntaxin interaction is required for nerve-evoked vesicle fusion rather than synaptic-vesicle priming. Thus, UNC-13 may regulate multiple steps of the synaptic-vesicle cycle.
Madison
Jon M
JM
Department of Molecular Biology, Massachusetts General Hospital, Simches Research Building, 185 Cambridge Street, Boston, Massachusetts 02114, USA.
Nurrish
Stephen
S
Kaplan
Joshua M
JM
D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics* / Q000502:physiology; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins; D004594:Electrophysiology; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D013395:Sucrose; D009435:Synaptic Transmission / Q000235:genetics / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism; D020798:Two-Hybrid System Techniques
D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D050765:Qa-SNARE Proteins; C083141:phorbol ester binding protein; D013395:Sucrose